CA1134021A - Pressure transducer having electrically shielded piezoresistive sensors - Google Patents
Pressure transducer having electrically shielded piezoresistive sensorsInfo
- Publication number
- CA1134021A CA1134021A CA329,874A CA329874A CA1134021A CA 1134021 A CA1134021 A CA 1134021A CA 329874 A CA329874 A CA 329874A CA 1134021 A CA1134021 A CA 1134021A
- Authority
- CA
- Canada
- Prior art keywords
- piezoresistive
- layer
- pressure transducer
- type
- electrically conductive
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
- 239000000463 material Substances 0.000 claims description 43
- 239000010931 gold Substances 0.000 claims description 20
- 229910052737 gold Inorganic materials 0.000 claims description 20
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 18
- PCHJSUWPFVWCPO-UHFFFAOYSA-N gold Chemical compound [Au] PCHJSUWPFVWCPO-UHFFFAOYSA-N 0.000 claims description 15
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 claims description 8
- 229910052710 silicon Inorganic materials 0.000 claims description 8
- 239000010703 silicon Substances 0.000 claims description 8
- 238000009825 accumulation Methods 0.000 claims description 7
- 239000004020 conductor Substances 0.000 claims description 6
- 238000009792 diffusion process Methods 0.000 claims description 4
- 239000002019 doping agent Substances 0.000 claims description 3
- 239000000615 nonconductor Substances 0.000 claims description 3
- 239000002210 silicon-based material Substances 0.000 claims description 3
- 230000008859 change Effects 0.000 abstract description 7
- 239000012530 fluid Substances 0.000 abstract description 5
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 19
- 239000011248 coating agent Substances 0.000 description 11
- 238000000576 coating method Methods 0.000 description 11
- 239000004065 semiconductor Substances 0.000 description 11
- 239000000377 silicon dioxide Substances 0.000 description 9
- 229960001866 silicon dioxide Drugs 0.000 description 9
- 235000012239 silicon dioxide Nutrition 0.000 description 9
- 230000035508 accumulation Effects 0.000 description 6
- 229920002120 photoresistant polymer Polymers 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 238000005530 etching Methods 0.000 description 3
- 238000000034 method Methods 0.000 description 3
- 208000036366 Sensation of pressure Diseases 0.000 description 2
- 230000006835 compression Effects 0.000 description 2
- 238000007906 compression Methods 0.000 description 2
- 238000005260 corrosion Methods 0.000 description 2
- 230000007797 corrosion Effects 0.000 description 2
- 239000010408 film Substances 0.000 description 2
- 230000010287 polarization Effects 0.000 description 2
- 230000008569 process Effects 0.000 description 2
- 230000004044 response Effects 0.000 description 2
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 description 1
- 230000009471 action Effects 0.000 description 1
- 238000009530 blood pressure measurement Methods 0.000 description 1
- 229910052796 boron Inorganic materials 0.000 description 1
- 239000000969 carrier Substances 0.000 description 1
- GPUADMRJQVPIAS-QCVDVZFFSA-M cerivastatin sodium Chemical compound [Na+].COCC1=C(C(C)C)N=C(C(C)C)C(\C=C\[C@@H](O)C[C@@H](O)CC([O-])=O)=C1C1=CC=C(F)C=C1 GPUADMRJQVPIAS-QCVDVZFFSA-M 0.000 description 1
- 230000002844 continuous effect Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 239000012535 impurity Substances 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 230000000873 masking effect Effects 0.000 description 1
- 238000001465 metallisation Methods 0.000 description 1
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- 230000004048 modification Effects 0.000 description 1
- 229920000136 polysorbate Polymers 0.000 description 1
- 239000011253 protective coating Substances 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000002441 reversible effect Effects 0.000 description 1
- 229910052814 silicon oxide Inorganic materials 0.000 description 1
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- 239000010409 thin film Substances 0.000 description 1
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Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
- G01L9/00—Measuring steady of quasi-steady pressure of fluid or fluent solid material by electric or magnetic pressure-sensitive elements; Transmitting or indicating the displacement of mechanical pressure-sensitive elements, used to measure the steady or quasi-steady pressure of a fluid or fluent solid material, by electric or magnetic means
- G01L9/0041—Transmitting or indicating the displacement of flexible diaphragms
- G01L9/0051—Transmitting or indicating the displacement of flexible diaphragms using variations in ohmic resistance
- G01L9/0052—Transmitting or indicating the displacement of flexible diaphragms using variations in ohmic resistance of piezoresistive elements
- G01L9/0054—Transmitting or indicating the displacement of flexible diaphragms using variations in ohmic resistance of piezoresistive elements integral with a semiconducting diaphragm
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
- H10D48/00—Individual devices not covered by groups H10D1/00 - H10D44/00
- H10D48/50—Devices controlled by mechanical forces, e.g. pressure
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Measuring Fluid Pressure (AREA)
- Pressure Sensors (AREA)
Abstract
- 14 - Case 4251 A PRESSURE TRANSDUCER HAVING ELECTRICALLY
SHIELDED PIEZORESISTIVE SENSORS
ABSTRACT OF THE DISCLOSURE
A diffused piezoresistive pressure transducer (10) is provided which is insensitive to surface charges which may develop in the use of the trans-ducer in a fluid-filled pressure transmitter assembly.
To accomplish this a metalized shield (20) is formed over the diffused piezoresistive sensors (Rc; Rt) as an integral part of the transducer (10). The metalized shield (20) is connected to an electrical supply source (V.D.C.) to allow any charge build-up on the shield surface (20) to be bled therefrom with i no change in the potential difference between the diffused piezoresistive sensors (Rt; Rc) and the shield (20).
SHIELDED PIEZORESISTIVE SENSORS
ABSTRACT OF THE DISCLOSURE
A diffused piezoresistive pressure transducer (10) is provided which is insensitive to surface charges which may develop in the use of the trans-ducer in a fluid-filled pressure transmitter assembly.
To accomplish this a metalized shield (20) is formed over the diffused piezoresistive sensors (Rc; Rt) as an integral part of the transducer (10). The metalized shield (20) is connected to an electrical supply source (V.D.C.) to allow any charge build-up on the shield surface (20) to be bled therefrom with i no change in the potential difference between the diffused piezoresistive sensors (Rt; Rc) and the shield (20).
Description
~3 ~
- 1 - Case 4251 A PRESSURE TRANSD~CER HAYING ELECTRICALLY
SHIELDED PIEZORESISTIVE SENSORS
TECHNICAL FIELD
The present invention relates to pressure trans-ducers generally and particularly to semiconductor pres-sure sensors having piezoresistive sensors diffused therein.
BACK~ROUND ART
Transducers which produce a resistance change in response to an applied pressure change have heretofore included thin film strain transducers as well as semi-conductor transducers.
Semiconductor pressure transducers are known wherein the strain gauge resistors are formed on one side of a monocrystalline semiconductor diaphragm such as Silicon having diffused therein a dopant such as boron. The sensing resistors are usually arranged on the diaphragm to form a bridge with the sensing resis-tors being`simultaneously in tension and compressionwhenever the diaphragm is deflected by a force or pressure applied to the surface of the diaphragm.
Many configurations of resistance elements on such Silicon diaphragms are known and examples of such
- 1 - Case 4251 A PRESSURE TRANSD~CER HAYING ELECTRICALLY
SHIELDED PIEZORESISTIVE SENSORS
TECHNICAL FIELD
The present invention relates to pressure trans-ducers generally and particularly to semiconductor pres-sure sensors having piezoresistive sensors diffused therein.
BACK~ROUND ART
Transducers which produce a resistance change in response to an applied pressure change have heretofore included thin film strain transducers as well as semi-conductor transducers.
Semiconductor pressure transducers are known wherein the strain gauge resistors are formed on one side of a monocrystalline semiconductor diaphragm such as Silicon having diffused therein a dopant such as boron. The sensing resistors are usually arranged on the diaphragm to form a bridge with the sensing resis-tors being`simultaneously in tension and compressionwhenever the diaphragm is deflected by a force or pressure applied to the surface of the diaphragm.
Many configurations of resistance elements on such Silicon diaphragms are known and examples of such
2 ~
- 2 - Case 4251 various configurations may be found in U.S. Patent No.
- 2 - Case 4251 various configurations may be found in U.S. Patent No.
3,537,319 as well as U.S. Patent No. 3,697,918.
Regardless of the resistance configuration, such pressure transducers utilizing diffused resistance strain gauges suffer from both long and short term drift problems which are caused by an accumulation of charges on the transducer surface hav;ng the straing gauges diffused therein. Such surface charges may arise from polariza-tion of fluid in contact with the transducer~ from exter-nal sources of voltage such as common mode voltage; as well as other such phenomena. The effec~ of a surface charge on the transducer may be descri~ed as follows.
Charges on the surface of an oxide layer covering a sem~-conductor ~ill induce image charges in the semiconductormateri al . For exampl e, i f the semiconductor ~s N-type, a negative surface charge induced on the ~ransducer surface will repel negative charges in the semiconductor caus~ng a reduction in the number of electrons in that area.
This is called "depletion" because the majority carriers in the semiconductor are depleted in that area. If a positive surface charge is induced on the surface of the oxide over the N-type transducer, an increase in the number of electrons in that area will occur. This action is termed "accumulation". The same effects occur with P-type material~ however the polarity of the voltages is reversed. In the case of the diffused piezoreslstive strain gauge, both-N- and P-type material are present.
The background material is N-type and the diffused resis-tors are P-type. When the strain gauge structure is sub-jected to the effect of surface chargPs on the oxide transducer surface the diffused resistors may change resistance and reverse leakage currents may increase resulting in eventual changes in the effective output of the strain gauge transducer.
~L3~
This forementioned phenomenon was observed by the inventors in the use of diffused piezoresistive pressure transducers as the pressure sensing element in a fluid-filled absolute pressure transmi-tter. When a voltage 5 source was connected between the housing of the pressure transmitter and either the -~ or - terminal of the source a slow change in the output of the pressure transmitter was detected having a time constant of between one-half and one hour. When the polarity of the voltage was reversed the output of the transmitter shifted in the opposite direction. The inventors suspected that a slow polarization of the fluid inside the housing of the pressure transmitter was occurring. Substitution of an AC electric source for the DC source reduced but did not eliminate the mentioned effect.
SUMMARY OF THE INVENTION
The present invention solves the forementioned problems associated with the known semiconductor diffused piezoresistive pressure transducer devices as well as others by providing an electricaLly shielded ~iffused piezoresistive pressure transducer which is insensitive to any surface charges developed on the surface of the transducer.
In accordance with the present invention there is provided a pressure transducer having shielded piezore-sistive strain gages comprising a base material of N-Type material, a piezoresistive P-Type material formed into said N-Type base material, an oxide layer extending over said P-Type piezoresistive material to act as an elec-trical insulator for said piezoresistive material, alayer of electrically conductive material extending over said oxide layer covering said piezoresistive material but being electrically isolated there-from, a direct current voltage source of a substantially constant potential value having a positive polarity side, and said direct current voltage source having its positive polarity 'f3~
Z~
- 3a --side elec-trically connected to hoth said electrically conductive ma-terial layer and said piezoresistive material to maintain said electrically conductive layer extending over said piezoresistive material at a known constant potential with respect to said piezoresistive material preventing the accumulation of any varying surface charge on said electrically conductive layer by draining of the surface charges into said voltage source.
In specific embodiments of the invention, the layer of electrically conductive material was made from Chrome-Gold .~
Regardless of the resistance configuration, such pressure transducers utilizing diffused resistance strain gauges suffer from both long and short term drift problems which are caused by an accumulation of charges on the transducer surface hav;ng the straing gauges diffused therein. Such surface charges may arise from polariza-tion of fluid in contact with the transducer~ from exter-nal sources of voltage such as common mode voltage; as well as other such phenomena. The effec~ of a surface charge on the transducer may be descri~ed as follows.
Charges on the surface of an oxide layer covering a sem~-conductor ~ill induce image charges in the semiconductormateri al . For exampl e, i f the semiconductor ~s N-type, a negative surface charge induced on the ~ransducer surface will repel negative charges in the semiconductor caus~ng a reduction in the number of electrons in that area.
This is called "depletion" because the majority carriers in the semiconductor are depleted in that area. If a positive surface charge is induced on the surface of the oxide over the N-type transducer, an increase in the number of electrons in that area will occur. This action is termed "accumulation". The same effects occur with P-type material~ however the polarity of the voltages is reversed. In the case of the diffused piezoreslstive strain gauge, both-N- and P-type material are present.
The background material is N-type and the diffused resis-tors are P-type. When the strain gauge structure is sub-jected to the effect of surface chargPs on the oxide transducer surface the diffused resistors may change resistance and reverse leakage currents may increase resulting in eventual changes in the effective output of the strain gauge transducer.
~L3~
This forementioned phenomenon was observed by the inventors in the use of diffused piezoresistive pressure transducers as the pressure sensing element in a fluid-filled absolute pressure transmi-tter. When a voltage 5 source was connected between the housing of the pressure transmitter and either the -~ or - terminal of the source a slow change in the output of the pressure transmitter was detected having a time constant of between one-half and one hour. When the polarity of the voltage was reversed the output of the transmitter shifted in the opposite direction. The inventors suspected that a slow polarization of the fluid inside the housing of the pressure transmitter was occurring. Substitution of an AC electric source for the DC source reduced but did not eliminate the mentioned effect.
SUMMARY OF THE INVENTION
The present invention solves the forementioned problems associated with the known semiconductor diffused piezoresistive pressure transducer devices as well as others by providing an electricaLly shielded ~iffused piezoresistive pressure transducer which is insensitive to any surface charges developed on the surface of the transducer.
In accordance with the present invention there is provided a pressure transducer having shielded piezore-sistive strain gages comprising a base material of N-Type material, a piezoresistive P-Type material formed into said N-Type base material, an oxide layer extending over said P-Type piezoresistive material to act as an elec-trical insulator for said piezoresistive material, alayer of electrically conductive material extending over said oxide layer covering said piezoresistive material but being electrically isolated there-from, a direct current voltage source of a substantially constant potential value having a positive polarity side, and said direct current voltage source having its positive polarity 'f3~
Z~
- 3a --side elec-trically connected to hoth said electrically conductive ma-terial layer and said piezoresistive material to maintain said electrically conductive layer extending over said piezoresistive material at a known constant potential with respect to said piezoresistive material preventing the accumulation of any varying surface charge on said electrically conductive layer by draining of the surface charges into said voltage source.
In specific embodiments of the invention, the layer of electrically conductive material was made from Chrome-Gold .~
- 4 - Case 4251 metallization layers and ~he layered coating shield was limited to areas covering the pressure sensitiYe resis- -tors of the pressure transducer.
In view of the foregoing it will be seen that one aspect of the presPnt invention is to provide an elec-trically shielded pressure transducer.
Yet another aspect of the present invention is to provide a pressure transduc~r insens;tive to surface charges which may develop on the transducer.
Yet another aspect of the present invention is to provide a pressure transducer wherein any surface charges are bled away through a suitable electrical connection of the transdueer shield.
These and other aspects of the present invention will be more clearly understood after a review of the following description of the preferred embodiment when considered w~th the accompanying drawings.
BRIEF D~SCRIPTION OF THE DRA~IINGS
2~ Fig. 1 ;s a top v;ew of the pressure transducer of the present invention.
Fig. 2 is a seotional side view of the pressure transducér taken along section 2-2 of Fig. 1.
Fig. 3 is an electrical schemat;c diagram showing the electrical connection of the surface charge shield of the pressure transducer of Figs. 1 and 2.
DESCRIPTION OF THE PREFERRED EMBCDIMENT
Referring now to the drawings wherein the showings are for purposes of d;sclosing a preferred embodiment of the invention and are not intended to l;mit the invention thereto, Figs. 1 and 2 show a semiconductor ~3~
In view of the foregoing it will be seen that one aspect of the presPnt invention is to provide an elec-trically shielded pressure transducer.
Yet another aspect of the present invention is to provide a pressure transduc~r insens;tive to surface charges which may develop on the transducer.
Yet another aspect of the present invention is to provide a pressure transducer wherein any surface charges are bled away through a suitable electrical connection of the transdueer shield.
These and other aspects of the present invention will be more clearly understood after a review of the following description of the preferred embodiment when considered w~th the accompanying drawings.
BRIEF D~SCRIPTION OF THE DRA~IINGS
2~ Fig. 1 ;s a top v;ew of the pressure transducer of the present invention.
Fig. 2 is a seotional side view of the pressure transducér taken along section 2-2 of Fig. 1.
Fig. 3 is an electrical schemat;c diagram showing the electrical connection of the surface charge shield of the pressure transducer of Figs. 1 and 2.
DESCRIPTION OF THE PREFERRED EMBCDIMENT
Referring now to the drawings wherein the showings are for purposes of d;sclosing a preferred embodiment of the invention and are not intended to l;mit the invention thereto, Figs. 1 and 2 show a semiconductor ~3~
- 5 - Case 4251 ~iezoresistive pressure transducer assembly 10 intended for use in a known fluid-filled pressure transmitter (not shown) which monitors the res;stance change of the transducer assembly 10 in response to pressure variations to thereby provide an indication of the pressure applied to the transducer assembly 10.
The pressure transducer assembly 10 has a base 12 consisting of bulk N type Silicon into which a P type ~ ron material is diffused to form a series of pressure ~ant'irsensitive resistors R. In the present assembly 10 five individual resistive patterns are diffused with the two ~, centrally located resistors R~ and R'c being the ~' resistors under compression in the use of the transducer assembly 10 in the pressure transmitter. The end rPsistors Rt and R't located along the periphery of the transduce~ assembly 10 in line with the compressive resistors Rc and R'c are the resistors which will be under tension in the use of tl)e transducer assembly 10 in the pressure transmitter. A fifth resistor Rk is located at right angles to the pressure sensitive resis-tors R to make the fifth resistor Kk pressure insensi-tive. The resistor Rk is diffused into the base 12 and may be used as a temperature compensation resistor.
In the diffusion process whereby a dopant is di F-fused into the N-type Silicon base to form the P-type diffused resistors a coating of Silicon-dioxide is formed along the entire face of the base into whi~ch the resistors are diffused. This Silicon-dioxide coat;ng acts as an electrical insulator and a protective coat-ing to the semiconductor device formed by the diffusion of impurities into the N-type base to form diffused resistors Rc; R'c; Rt, R'~. This Silicon-dioxide coat-ing is selectively removed in a manner that will be described later to leaYe a coating 14 over the surface 3~ ~2 ~
The pressure transducer assembly 10 has a base 12 consisting of bulk N type Silicon into which a P type ~ ron material is diffused to form a series of pressure ~ant'irsensitive resistors R. In the present assembly 10 five individual resistive patterns are diffused with the two ~, centrally located resistors R~ and R'c being the ~' resistors under compression in the use of the transducer assembly 10 in the pressure transmitter. The end rPsistors Rt and R't located along the periphery of the transduce~ assembly 10 in line with the compressive resistors Rc and R'c are the resistors which will be under tension in the use of tl)e transducer assembly 10 in the pressure transmitter. A fifth resistor Rk is located at right angles to the pressure sensitive resis-tors R to make the fifth resistor Kk pressure insensi-tive. The resistor Rk is diffused into the base 12 and may be used as a temperature compensation resistor.
In the diffusion process whereby a dopant is di F-fused into the N-type Silicon base to form the P-type diffused resistors a coating of Silicon-dioxide is formed along the entire face of the base into whi~ch the resistors are diffused. This Silicon-dioxide coat;ng acts as an electrical insulator and a protective coat-ing to the semiconductor device formed by the diffusion of impurities into the N-type base to form diffused resistors Rc; R'c; Rt, R'~. This Silicon-dioxide coat-ing is selectively removed in a manner that will be described later to leaYe a coating 14 over the surface 3~ ~2 ~
- 6 - Case 4251 o~ the base except in th~ electrical cont~ct areas 16 for resistors Rc; R'Ci Rti R't and to facilitate elec-trical connection of Rc to Rt.
Consi~ering the structure so far, it will be seen that a functioning semiconductor pressure transducer assembly can be had by providing electrical contact to ~he contact points 16 in the areas where the Silicon-dioxide has been removed allowing the measure of the resistance changes across Rc; R'c; Rt and R'~. However, as was mentioned in the prior art description surface charge build-up may cause either depletion or accumula-tion whlch would tnterfere with the steady state conti-nuous operation of the transducer assembly 10 mounted into a pressure transmitter. To allevlate this problem;
a coating of Chrome material 18 having a thickness be-tween 750 to 1000 Angstroms is deposited over the resis-tors Rc; ~'~; Rt; R't followed by a coat of Gold material e.
20 having a thickness of approximat-ely 5000 Angstroms over thé Chrome material. Thle Chrome 18 material is de-posited first since the Gold 20 does nat adhere as easily to the N-type Silicon 12 and Silicon-oxide 14 whereas Chrome 18 does. On the other hand, Gold 20 adheres very well to a Chrome 18 coating and since it is the Gold 20 coating that is desirable for corrosion resistance and high electrical conductivity the Chrome 18 coating is used as an intermediate layer. The temperature compen-sation resistor Rk is not coated with the Chrome 18 Gold 20 shielding layer since it does not come into play in the ac~ual pressure measurement as do the resis-tors Rc and Rt. ~or convenience in fabrication, contact to the diffused resistors Rc; R'c; Rtg R't is made with the same Chrome-Gold coating as is used for the shie`ld, leads being extended across the surface of the Silicon-dioxide to large pads for attachment of wires from an 3 ~
Consi~ering the structure so far, it will be seen that a functioning semiconductor pressure transducer assembly can be had by providing electrical contact to ~he contact points 16 in the areas where the Silicon-dioxide has been removed allowing the measure of the resistance changes across Rc; R'c; Rt and R'~. However, as was mentioned in the prior art description surface charge build-up may cause either depletion or accumula-tion whlch would tnterfere with the steady state conti-nuous operation of the transducer assembly 10 mounted into a pressure transmitter. To allevlate this problem;
a coating of Chrome material 18 having a thickness be-tween 750 to 1000 Angstroms is deposited over the resis-tors Rc; ~'~; Rt; R't followed by a coat of Gold material e.
20 having a thickness of approximat-ely 5000 Angstroms over thé Chrome material. Thle Chrome 18 material is de-posited first since the Gold 20 does nat adhere as easily to the N-type Silicon 12 and Silicon-oxide 14 whereas Chrome 18 does. On the other hand, Gold 20 adheres very well to a Chrome 18 coating and since it is the Gold 20 coating that is desirable for corrosion resistance and high electrical conductivity the Chrome 18 coating is used as an intermediate layer. The temperature compen-sation resistor Rk is not coated with the Chrome 18 Gold 20 shielding layer since it does not come into play in the ac~ual pressure measurement as do the resis-tors Rc and Rt. ~or convenience in fabrication, contact to the diffused resistors Rc; R'c; Rtg R't is made with the same Chrome-Gold coating as is used for the shie`ld, leads being extended across the surface of the Silicon-dioxide to large pads for attachment of wires from an 3 ~
- 7 - Case 4251 external source.
In mounting the transducer assembly 10 in a pressure transmitter, the transducer assembly 10 is usually bonded to a hollow support structure 17 which allows pressure to be applied to the resistors Rc; R'c, Rt; R't- To facilitate the alignment of the transducer assembly 10 to this support structure 17 a ser;es of alignment rlngs ?2 are formed on the face of the transducer assembly 10 defining the inner circum-ference 19 of the support structure 17 and requiring the alignmen$ of this circumference defined by the rings 22 with the actual circumference 19 of the suppor~ structure 17.
Referring now to Fig. 3, it will be seen that when the transducer assembly 10 is mounted in a pres-sure transmitter the following electrical connections are made to only the sensing resistors Rc and Rt as well as to the Chrome 18 Gold 20 shielding layer coverlng the sensing resistors Rc and Rt. In the present embodiment only the resistor in compression Rc is used in c~njunction with its adjoin;ng resistor in tension Rt. A DC voltage source of approximately 10 volts is applied across the series connected resistors Rc and Rt and the output of the res;stor ;n tension Rt is monitored. As the pressure applied to the trans-ducer assembly 10 is varied, the resistance of the resistors Rc and Rt also varies in a known ~anner there by allowing the voltage and/or current variation across the resistor Rt to provide the indication of pressure.
As is seen, the Chrome 18 Gold 20 shields covering the resistors Rc and Rt are electrically connected by a jumper wire 24 with the two shields then being con-nected by a connection 26 to the posit;ve side of the 10 volt DC power source. The connection 26 in the ~3~
In mounting the transducer assembly 10 in a pressure transmitter, the transducer assembly 10 is usually bonded to a hollow support structure 17 which allows pressure to be applied to the resistors Rc; R'c, Rt; R't- To facilitate the alignment of the transducer assembly 10 to this support structure 17 a ser;es of alignment rlngs ?2 are formed on the face of the transducer assembly 10 defining the inner circum-ference 19 of the support structure 17 and requiring the alignmen$ of this circumference defined by the rings 22 with the actual circumference 19 of the suppor~ structure 17.
Referring now to Fig. 3, it will be seen that when the transducer assembly 10 is mounted in a pres-sure transmitter the following electrical connections are made to only the sensing resistors Rc and Rt as well as to the Chrome 18 Gold 20 shielding layer coverlng the sensing resistors Rc and Rt. In the present embodiment only the resistor in compression Rc is used in c~njunction with its adjoin;ng resistor in tension Rt. A DC voltage source of approximately 10 volts is applied across the series connected resistors Rc and Rt and the output of the res;stor ;n tension Rt is monitored. As the pressure applied to the trans-ducer assembly 10 is varied, the resistance of the resistors Rc and Rt also varies in a known ~anner there by allowing the voltage and/or current variation across the resistor Rt to provide the indication of pressure.
As is seen, the Chrome 18 Gold 20 shields covering the resistors Rc and Rt are electrically connected by a jumper wire 24 with the two shields then being con-nected by a connection 26 to the posit;ve side of the 10 volt DC power source. The connection 26 in the ~3~
- 8 - Case 4251 F~g. 1 embodiment is actual'ly one of the runners 20 going to the external c~rcumference pad for external wire ronnection. This çonnection of the Gold 20 5 Chrome 18 shield to the same power source as is power-ing the resistors Rc and Rt seems to hold the shield at a fixed potential w;th respect to the base and pre-vents the accumulation of any surface charge over the res;stors Pc and Rt which would change the~r effective values and the output from the sensor in the manner previously described. As a consequence, no ch~nging image charges from any surface charge is possible since any excess charge tending to induce a shield voltage different than the 10 volt measuring circuit voltage lS would be drained off into the voltage source. As a re-sult the previously discussed drift problems normally assoc~ated with such sensing resistors subject to sur-face charge accumulation ;s effectively eliminated.
Next referring 'back to Figs. 1 and 2, a clear understanding of the p~essure transducer assembly 10 will be had after the following d~scussion of the method 'whereby the assembly 10 is manufactured.
As mentioned earlier, P-type resistors are dif-fused into the N-type base to form resistors R~; R'c;
Rt~ ~'t- As a consequence of this diffusion process, a coating of Silicon-dioxide is formed on the entire top surface 2~ of the N-type Silicon-material 12. To provide electrical contacts f'or the resistors Rc; R'c, Rt; R'ti and Rk, a series o~ points 16 is etched away using known etching techniqures extending down to the P-type Silicon material forming the piezoresistors Rc;
R'c; R~; R't as well as the temperature compensating resistor Rk to provide electrical contacts therefore.
The Silicon-dioxide material is also etched away in the area extending from the circumference 30 all the .
g _ Case 4251 way to the end of the sides 32 of the'pressure trans-ducer assembly 10. This etched away area provides a contact area used to easily connect the Chrome-Go1d 5 shield 18, 20 extending over the resistor Rt with the Chrome-Gold shield 18, 20,extending over the resistor Rc by connecting the jumper ~J;re ?4 between the area " outside of the circumference 30 and the shield 18, ?0 over the resistor Rc. It will be noted that the shield 10 18~ 70 over the resistor,~ will be connected to the etched area extending beyond the circumference 30 through runners 34 formed during the latter described , process. To form the surface shield over the resistors , Rc, R'c, Rt; R't a coating 18 of Chrome is vacuum~
15 evaporated on the entire surface of the base 12 includ-', ing the etched and unetched portions. This well-known vacuum-evaporation process is cont~nued unt~l the Chrome coatlng 18 ls deposited to a thickness of between 750 to 1000 Angstroms. Chrome ls used since lt has excellent adhering qualities to the N-type Sil~con material as well as the Silicon-dioxide m,aterial as well as provid-~ng the' desired amount of electrical conductivity. A
5000 Angstrom layer of Gold film 20 is next vacuum-evaporated on to the entire Chrome film 18. Gold pro-vides excellent adherence to IChrome as well as eorro-sion resistance and excellent electrical conductiYity.
The reason that Gold 20 is not deposited directly on to the N-type Silicon and the Silicon-dioxide surface is that Gold although desirable for purposes of corrosion resistance and electrical conductivity provides rela-tively poor adherence to the forenamed surfaces while providing excellent adherence to the Chrome surface 18.
Next, photoresist material is applied to the entire Gold surface 20 and the photoresist covered surface is then exposed through a mask which allows the areas 3 4~
- 10 - Case 4251 shown as 209 and 22 in Fig. 1 to be exposed while masking the areas shown as 14 in Fig. 1. The mask is then removed and the photoresist material is developed in a known manner which removes the unexposed photo-resist material ~rom the a,reas designated as 14 in Fig. 1. Next, known etching materials are used to etch away the Gold in areas which are not protected by the photoresist material followed by etching away the Chrome from these same areas not protected by photo-resist materialO Separate etchan~ materials are used to individually etch away the Gold and the Chrome sînce a universal etchant effective in simultaneously ; removing both of these materials has not been found to be effective. The forego~ng steps leave a finished transducer assembly 10 as shown in Figs, 1 and 2.
Although a topcoating could be now placed over the entire'assembly, the need for such has not been found to be necessary.
Certa~n modifica~ions and improvements will occur to those skilled in the art upon reading this speciFication. It will be understood that all such improvements and modifications have been del eted ~ herein for the sake oF conciseness and readability but - 25 are properly covered within the scope of the following claims.
Next referring 'back to Figs. 1 and 2, a clear understanding of the p~essure transducer assembly 10 will be had after the following d~scussion of the method 'whereby the assembly 10 is manufactured.
As mentioned earlier, P-type resistors are dif-fused into the N-type base to form resistors R~; R'c;
Rt~ ~'t- As a consequence of this diffusion process, a coating of Silicon-dioxide is formed on the entire top surface 2~ of the N-type Silicon-material 12. To provide electrical contacts f'or the resistors Rc; R'c, Rt; R'ti and Rk, a series o~ points 16 is etched away using known etching techniqures extending down to the P-type Silicon material forming the piezoresistors Rc;
R'c; R~; R't as well as the temperature compensating resistor Rk to provide electrical contacts therefore.
The Silicon-dioxide material is also etched away in the area extending from the circumference 30 all the .
g _ Case 4251 way to the end of the sides 32 of the'pressure trans-ducer assembly 10. This etched away area provides a contact area used to easily connect the Chrome-Go1d 5 shield 18, 20 extending over the resistor Rt with the Chrome-Gold shield 18, 20,extending over the resistor Rc by connecting the jumper ~J;re ?4 between the area " outside of the circumference 30 and the shield 18, ?0 over the resistor Rc. It will be noted that the shield 10 18~ 70 over the resistor,~ will be connected to the etched area extending beyond the circumference 30 through runners 34 formed during the latter described , process. To form the surface shield over the resistors , Rc, R'c, Rt; R't a coating 18 of Chrome is vacuum~
15 evaporated on the entire surface of the base 12 includ-', ing the etched and unetched portions. This well-known vacuum-evaporation process is cont~nued unt~l the Chrome coatlng 18 ls deposited to a thickness of between 750 to 1000 Angstroms. Chrome ls used since lt has excellent adhering qualities to the N-type Sil~con material as well as the Silicon-dioxide m,aterial as well as provid-~ng the' desired amount of electrical conductivity. A
5000 Angstrom layer of Gold film 20 is next vacuum-evaporated on to the entire Chrome film 18. Gold pro-vides excellent adherence to IChrome as well as eorro-sion resistance and excellent electrical conductiYity.
The reason that Gold 20 is not deposited directly on to the N-type Silicon and the Silicon-dioxide surface is that Gold although desirable for purposes of corrosion resistance and electrical conductivity provides rela-tively poor adherence to the forenamed surfaces while providing excellent adherence to the Chrome surface 18.
Next, photoresist material is applied to the entire Gold surface 20 and the photoresist covered surface is then exposed through a mask which allows the areas 3 4~
- 10 - Case 4251 shown as 209 and 22 in Fig. 1 to be exposed while masking the areas shown as 14 in Fig. 1. The mask is then removed and the photoresist material is developed in a known manner which removes the unexposed photo-resist material ~rom the a,reas designated as 14 in Fig. 1. Next, known etching materials are used to etch away the Gold in areas which are not protected by the photoresist material followed by etching away the Chrome from these same areas not protected by photo-resist materialO Separate etchan~ materials are used to individually etch away the Gold and the Chrome sînce a universal etchant effective in simultaneously ; removing both of these materials has not been found to be effective. The forego~ng steps leave a finished transducer assembly 10 as shown in Figs, 1 and 2.
Although a topcoating could be now placed over the entire'assembly, the need for such has not been found to be necessary.
Certa~n modifica~ions and improvements will occur to those skilled in the art upon reading this speciFication. It will be understood that all such improvements and modifications have been del eted ~ herein for the sake oF conciseness and readability but - 25 are properly covered within the scope of the following claims.
Claims (4)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A pressure transducer having shielded piezoresistive strain gages comprising:
a base material of N-Type material;
a piezoresistive P-Type material formed into said N-Type base material;
an oxide layer extending over said P-Type piezoresistive material to act as an electrical insulator for said piezoresistive material;
a layer of electrically conductive material extending over said oxide layer covering said piezoresis-tive material but being electrically isolated therefrom;
a direct current voltage source of a substantially constant potential value having a positive polarity side; and said direct current voltage source having its positive polarity side electrically connected to both said electrically conductive material layer and said piezoresistive material to maintain said electrically conductive layer extending over said piezoresistive material at a known constant potential with respect to said piezoresistive material preventing the accumulation of any varying surface charge on said electrically conductive layer by draining of the surface charges into said voltage source.
a base material of N-Type material;
a piezoresistive P-Type material formed into said N-Type base material;
an oxide layer extending over said P-Type piezoresistive material to act as an electrical insulator for said piezoresistive material;
a layer of electrically conductive material extending over said oxide layer covering said piezoresis-tive material but being electrically isolated therefrom;
a direct current voltage source of a substantially constant potential value having a positive polarity side; and said direct current voltage source having its positive polarity side electrically connected to both said electrically conductive material layer and said piezoresistive material to maintain said electrically conductive layer extending over said piezoresistive material at a known constant potential with respect to said piezoresistive material preventing the accumulation of any varying surface charge on said electrically conductive layer by draining of the surface charges into said voltage source.
2. A pressure transducer as set forth in claim 1 wherein said layer of electrically conductive material covering said oxide layer includes a layer of Chrome material having a layer of Gold material thereon.
3. A pressure transducer as set forth in claim 2 wherein said layer of Chrome-Gold material is electrically connected to a voltage source.
4. A pressure transducer as set forth in any one of claims 1, 2 and 3 wherein said base material is N-type Silicon and wherein said piezoresistive material is a P-type Silicon material formed by the diffusion of a dopant into said N-type Silicon base material.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US93730478A | 1978-08-28 | 1978-08-28 | |
| US937,304 | 1978-08-28 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1134021A true CA1134021A (en) | 1982-10-19 |
Family
ID=25469756
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA329,874A Expired CA1134021A (en) | 1978-08-28 | 1979-06-15 | Pressure transducer having electrically shielded piezoresistive sensors |
Country Status (9)
| Country | Link |
|---|---|
| JP (1) | JPS5533092A (en) |
| AU (1) | AU503379B1 (en) |
| BR (1) | BR7902641A (en) |
| CA (1) | CA1134021A (en) |
| DE (1) | DE2921043C2 (en) |
| ES (2) | ES480076A1 (en) |
| FR (1) | FR2435022A1 (en) |
| GB (1) | GB2029094B (en) |
| IT (1) | IT1112793B (en) |
Families Citing this family (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4327350A (en) * | 1979-07-17 | 1982-04-27 | Data Instruments, Inc. | Pressure transducer |
| JPS5796573A (en) * | 1980-12-08 | 1982-06-15 | Hitachi Ltd | Semiconductor strain transducer |
| JPS58197780A (en) * | 1982-05-14 | 1983-11-17 | Hitachi Ltd | Semiconductor pressure converter |
| JPS59230101A (en) * | 1983-06-13 | 1984-12-24 | Tokyo Electric Co Ltd | Distortion sensor |
| CA1314410C (en) * | 1986-12-08 | 1993-03-16 | Masanori Nishiguchi | Wiring structure of semiconductor pressure sensor |
| FR2643148B1 (en) * | 1989-02-15 | 1991-12-06 | Schlumberger Ind Sa | SEMICONDUCTOR-ON-INSULATION PRESSURE SENSOR |
| DE102007057877A1 (en) | 2007-11-29 | 2009-06-04 | Endress + Hauser Gmbh + Co. Kg | pressure sensor |
| CN116222839B (en) * | 2023-05-09 | 2023-07-18 | 苏州亿波达光电子科技有限公司 | Sensing element and pressure sensor |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE875879C (en) * | 1951-07-25 | 1953-05-07 | Land | Shielding method for strain gauges |
| GB1265018A (en) * | 1968-08-27 | 1972-03-01 | ||
| US4050049A (en) * | 1976-02-09 | 1977-09-20 | Signetics Corporation | Solid state force transducer, support and method of making same |
| FR2367280A1 (en) * | 1976-10-08 | 1978-05-05 | Schlumberger Ind Sa | STRAIN GAUGE SENSOR EQUIPPED WITH A TEMPERATURE SENSOR |
| JPS54131892A (en) * | 1978-04-05 | 1979-10-13 | Hitachi Ltd | Semiconductor pressure converter |
-
1979
- 1979-03-01 AU AU44732/79A patent/AU503379B1/en not_active Ceased
- 1979-03-21 GB GB7909862A patent/GB2029094B/en not_active Expired
- 1979-04-27 BR BR7902641A patent/BR7902641A/en unknown
- 1979-04-28 ES ES480076A patent/ES480076A1/en not_active Expired
- 1979-04-28 ES ES480075A patent/ES480075A1/en not_active Expired
- 1979-04-30 IT IT22259/79A patent/IT1112793B/en active
- 1979-05-23 DE DE2921043A patent/DE2921043C2/en not_active Expired
- 1979-06-15 CA CA329,874A patent/CA1134021A/en not_active Expired
- 1979-06-28 FR FR7916710A patent/FR2435022A1/en active Granted
- 1979-07-27 JP JP9516179A patent/JPS5533092A/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| AU503379B1 (en) | 1979-08-30 |
| BR7902641A (en) | 1980-03-18 |
| GB2029094A (en) | 1980-03-12 |
| IT1112793B (en) | 1986-01-20 |
| JPS5533092A (en) | 1980-03-08 |
| GB2029094B (en) | 1983-01-26 |
| FR2435022A1 (en) | 1980-03-28 |
| ES480076A1 (en) | 1979-11-16 |
| IT7922259A0 (en) | 1979-04-30 |
| FR2435022B1 (en) | 1983-04-01 |
| DE2921043A1 (en) | 1980-03-13 |
| ES480075A1 (en) | 1979-11-16 |
| DE2921043C2 (en) | 1985-07-04 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |