DE1225765C2 - Electrical capacitor with voltage-dependent capacitance, consisting of a semiconductor body - Google Patents

Description

The invention relates to an electrical condensate condition applies regardless of which value

Sator with voltage-dependent capacitance, which takes up the capacitance C, which exists in the unified semiconductor body and which, in particular, ^{sets a 6} ° strengthening process. Only the inequality for the parametric amplification of microwaves 1 1

serves. <β ω <s

It is well known that an oscillation circuit Rp-C R ₈ -C

with a non-linear reactance, which must be met.

Apply a first oscillation with a large amplitude 65 .. I ₁₁ . ... "

" E α · c uu -UJ-PL- u In order to keep"" small, further advance

aut the subharmonics of this oscillation - Rp-C

is true, a subharmonic oscillation is generated. be set that R _{v represents} a relatively large amount to control the generated subharmonic resistance. This is the case when the

pn junction is polarized in the reverse direction. A common value for the resistance R _p is 10 ⁵ to 10 ^e ohms for germanium and 10 ⁷ to 10 ⁸ ohms for silicon.

In order for '"■" to be very large, C and R _{must have 8}

K ₈ -C

be very small. As is known, the capacitance C can be brought to approximately 1 pF and the resistance Rs to approximately 1 ohm.

With these conditions, the result is a

Kp · C

Value of about 1 MHz for germanium, which drops to 10 kHz for silicon. In contrast, the 1

Side of the transition, namely in the area of lower conductivity, this area is known to have a large cross-section up to the vicinity of the Assigned to the transition zone. In this case the resistance is not inversely proportional to the Barrier area but is given by the following equation definitely:

2nb

Value for

- = - several hundred GHz.

The smaller the resistance R _s , the lower the noise figure. The actual amplifier is formed by the reactance of the pn junction and the noise source by the ohmic resistance R _s .

The maximum gain of a parametric amplifier is for the upper sideband for microwaves the following equation is expressed:

/ ι

Here, J _{1 is} the frequency of the signal to be amplified, / 2 is the frequency of the amplified signal, (/ ₂ - / 1) is the frequency of the auxiliary generator whose power is used to amplify the signal with the frequency J ₁ .. χ is a reduced variable which results from the following equation:

with μ = \ l ^C ™ ^ax . That is, μ is equal to the square

\ C min

root from the ratio of the extreme values that the variable capacitance can assume at the pn junction. The calculated, optimal value for this is 1 + j / 2; fc = ■, η ^ represents the figure of merit of the pn over-

Z π K ₈ - C _mm

gangs, expressed as the cutoff frequency. The capacitance C _min is the capacitance of the reverse-biased pn junction at a voltage that is somewhat lower than the breakdown voltage, ie the maximum permissible reverse voltage.

In the case of a parametric amplifier for the lower sideband it also results that the pn junction The higher the figure of merit / eist, the higher the frequency, the higher the vibrations.

The above statements clearly show that the reinforcement properties of a parametric amplifier depend on the product of minimum capacitance Cmin and series resistance R _s and on the ratio of maximum capacitance to minimum capacitance. According to S h ο ck 1 ey, the minimum capacity C _n H _{n is given by the following formula:}

C "" - "= - Ka * -SV: 'l

Thereof is V _ma x the applied reverse voltage less the contact stress, the gradient of the distribution of the foreign atoms in the area of the pn junction, S α the cross sectional area of the pn junction and K is a constant.
Since the resistance R ₃ is essentially on a Here, ρ is the specific resistance in ohms of the area under consideration and b is the radius of the pn junction in centimeters, assumed to be circular. Since ρ = π b ^% , formula 3 results

The formulas 2 and 4 show that the capacitance C _m % _{n is} proportional to the cross section of the pn junction, while the resistance R _{s increases} inversely proportional to the square root of the cross section. The product R ₈ · Cmin varies with the square root of the cross section S, which must therefore be small. In order to reduce the resistance R ₈ , the specific resistance ρ could also be reduced by increasing the doping of the semiconductor body; However, this measure causes a reduction in the maximum permissible reverse voltage and has the consequence that the value to be achieved for the minimum capacitance Cmin is increased.

If low values of resistivity ρ and are to be obtained for the cross section S, then so must be avoided that certain limits are reached, because otherwise the maximum reverse voltage V _ma x at the pn junction is too low for any application purpose. ',

The best results achieved so far have been obtained with silicon diodes with diffusion transitions with a distribution gradient of the foreign atoms of 10 ²³ to 10 ²⁴ atoms / cm ⁴ . The figure of merit here is 60 to 120 GHz and can also reach 200 GHz, depending on the situation.

The object of the invention is now the pn junction of a semiconductor body, which as Capacitor with voltage-dependent capacitance is used for parametric amplifiers for microwaves, so to shape that a higher figure of merit with a. lower noise figure compared to the previously known

pn transitions is achieved in semiconductor bodies,

ie the ratio C _max : Cmin should reach an optimal value. In addition, a production method is to be described which allows the production tolerances of such semiconductor bodies to be kept within satisfactory limits.

The task is solved by an electrical capacitor with a voltage-dependent capacitance,

6ü which consists of a semiconductor body that is shown in its interior a planar pn-junction as well as a distribution gradient of the foreign atoms between the two electrodes via the pn junction and the one with the pn junction in Has connected zone, the cross-sectional area of which is parallel to the pn junction changes steadily with the distance from the pn junction, the distribution gradient according to the invention being the

Foreign atoms in the vicinity of the pn junction is 10 ^ie to 10 ²¹ foreign atoms per cubic centimeter and per centimeter and the zone with constant cross-sectional change is conical and the angle Θ between the plane of the pn junction and the surface of the cone is between 1 and 10 ° and the pn junction lies within the conical zone.

The manufacturing process of such an electrical capacitor according to the invention consists in that the semiconductor body is cut from a monocrystal, which by pulling at one of the desired distribution gradient of the foreign atoms of the transition layer corresponding speed is obtained, and that this semiconductor body is then placed in an electrolytic bath at the reverse Voltage is brought to in the η range of the semiconductor in the immediate vicinity of the pn junction to form a constriction in such a way that the semiconductor towards the p-region to a very obtuse cone comprising the pn junction and the pn junction the desired one Area extension received.

The invention is described in more detail below for an exemplary embodiment with reference to the drawings explained. It shows

F i g. 1 shows a semiconductor body according to the invention,

F i g. 2 the charge carrier distribution on both sides of the pn junction,

F i g. 3 shows a graph in which the capacitance C is shown as a function of the applied voltage for various semiconductor bodies.

In FIG. 1, the η region is denoted by 1 and the p region is denoted by 3. The pn junction is denoted by 2. Contacts that are independent of the pn junction are denoted by 4 and 5.

A very flat truncated cone or cone, which has a constriction in the η region, adjoins the p region 3. The pn junction is not located at the point of the minimum cross section, but in the conical zone, specifically where the change in cross section is greatest. In this way, a large change in capacitance is achieved as a function of the applied voltage, so that the capacitance value increases faster than proportionally with the reciprocal value of the cube root of the voltage. If a pn-junction of a known semiconductor is considered under the effect of an applied voltage Kai's capacitor, the surfaces of which are the areas of opposite charge on one and the other side of the junction, then it is known that the capacitance is inversely proportional to the cube root of the voltage V changes, it being possible to assume that the surface of these deposits remains constant, while the distance between the deposits follows the above law.

If the pn junction, as shown in FIG. 1 and 2, is located in the conical zone of the semiconductor body, the generatrix of which forms an angle <~) with the plane of the pn junction, which is very small, then an increase in the voltage V causes a reduction in the surface of the capacitor coating, depending the distance between the pads becomes larger, while the surface of the other condenser pad increases slightly at the same time. In the case of the semiconductor body according to the invention, this results

accordingly, a reduction in the surface of the capacitor plate when the distance between its coverings is enlarged, proportionally with the cube root, which is therefore associated with a reduction in capacity that is faster than that by

the law V ^{5 is} given. This increasing non-linearity of the change in capacitance as a function of the applied voltage can be clearly seen from the comparison of curves 1 and 2 in FIG. 3, which were determined empirically.

Curve 1 corresponds to a pn junction which is arranged in a semiconductor body according to the invention, a distribution gradient of the foreign atoms of 10 ²⁰ atoms / cm ⁴ , a circular cross section of the pn junction with a diameter of 100 μ being provided, which is so is arranged in the conical part of the semiconductor body, as shown in FIG. 1 and 2 is shown. The angle Θ is a few degrees. In this way the factor achieves

μ =

almost the theoretical optimal value 1 - \ - ] / 2.

Curve 2 corresponds to a pn transition with the same distribution gradient and the same cross-section, but the pn junction is arranged in the narrowest part of the constriction, d. H. in one cylindrical profile, the generatrix of which forms an angle of 90 ° with the plane of the pn junction.

Curve 3 is plotted for comparison, using the same scale as curves 1 and 2. It shows the change in capacitance as a function of the applied voltage for a "mesadiode" made of silicon with a distribution gradient of 10 ²³ to 10 ²⁴ atoms / cm ⁴ and the pn junction is undergrebacht in an almost cylindrical profile.

The semiconductor body according to the invention also has the advantage that the resistance Rg of the pn junction decreases slightly when the applied voltage increases. The resistance R _s is essentially formed by the p-area, ie by the area where the larger capacitor plate is located, the surface of which, as can easily be seen, increases with increasing voltage V , so that the resistance R ₈ inevitably becomes smaller. With the electrical capacitor described above, a parametric amplifier with maximum gain and lowest noise figure can be built.

The manufacturing method for such an electric nonlinear capacitance capacitor according to the invention is the following:

A semiconducting substance, preferably germanium, is used to make a monocrystal which has two regions, namely an n region and a p region. Provided that the When the transition from ρ to η is completed, the manufacturing steps are as follows:

1. A certain proportion of foreign atoms of the acceptor type such as indium is in the germanium bath or gallium introduced to form a half-liter area of the type ρ with a certain specific resistance to echo.

7 8

2. Pulling a monocrystal in the p-area with certain cross-section to get that in a cone certain length. shaped zone with an optimal point angle.

3. With continued pulling, the monocrystal is ordered.

will, possibly to an increasing extent, the following are the most important

Correct proportion of donor foreign atoms such as 5 dimensions, the Hsrsteüungsangibsn and the

Antimony or arsenic added to the band characteristics of a pn semiconductor

to pass from type ρ to type η, so invention ang ^ gsb ^ n wsrdan, dir to paramstric

that a certain specific resistance can be used in amplification bsi microwaves. η area is achieved.

,, τ? . . - ry. ,, .,. . ",. ίο Dimensions of a semiconductor rod:

4. Continue pulling the mono stall until

to achieve a certain length of the length of the η region 2 mm

η range. Length of the p-region 1 mm

5. Dividing the monocrystal into several cylindri- diameters of the ^

see paraUelepipedic rods with a small dis- 15 KhmlTef of the pin ^μ

measurements by means of a saw or an ultra-micrometer of the

sound system, each of these rods having a value of around 70 to 80 μ

contains pn junction. The length of these rods inclination angle about 1 b, s 10 °

SX Gr £ orn _g a5rnm, ^QUerSChnitt *. Manufacturing information:

6. Solder the barrier layer-free contacts 4 and 5 material of the semiconductor .. Germanium to these chopsticks. Specific resistance

_ 'iv. . , '', of ^the P-area 0.01 ohm / cm

7. Plating the non-barrier-layer contacts 4 Resistivity

and 5 with a protective varnish. The rods ₂₅ in the n-area ...'.... 0.002 Ohm / cm

are placed in an electrolytic bath, distribution gradient of

around them then a selective electro- foreign atoms 10 ²⁰ atoms / cm ⁴

to undergo lytic treatment. The drawing speed ..... 200 mm / hour

drive is that the pre-electrolytic treatment in the reverse direction 5 to 10 mA during

stressed semiconductors with its transition ₃₀ 2 to 3 hours

resistance bridged by the electrolyte during 2 to 4 mA

is, making the various places of the half-hour approximately 1 hour

conductor body more or less, depending on the specific resistance

Working conditions to be attacked by the electrolyte ·. greater than 1000 ohms

which the conductivity of the electrolyte has a ₃₅

plays a special role. Characteristics of the semiconductor according to the invention:

Resistance in the

. By suitable choice of the electrolyte, the time direction [R _s ] 0.6 ohms

the action of electrolysis and the current intensity Minimum capacity [C _{m (n} ] 0.25 pF

In this way it is possible to make a pn transition ₄₀ figure of merit [/ _c ] 1000 GHz.

1 sheet of drawings

309 620/436

Claims (4)

1 2 patent claims - a subharmonic control signal of low amplitude is also applied to the oscillating circuit, then such an arrangement shows amplifier properties 1.Electric capacitor with voltage and is called parametric amplifier,
dependent capacitance, consisting of a semi-semiconductor 5 as a non-linear reactance or conductor body, which uses a flat pn junction at sufficiently high frequencies as an oscillating pn junction and a distribution circle with non-linear capacitance, is the gradient of the foreign atoms between the two also known. The transition layer of a pn-half-electrode over the pn-junction has a variable capacitance depending on the applied reverse voltage known to form a semiconductor body with variable-parallel cross-sectional area continuously with beer capacitance in such a way that its cross-sectional area parallel to the pn-junction changes with the distance from the pn-junction changes (Austrian gradient of the foreign atoms in the vicinity 15 Reichische Patent 180 958). of the pn junction 10 ¹⁹ to 10 ²¹ foreign atoms per It is also known to have a semiconductor body Cubic centimeter and per centimeter is that the pn-junction is to be etched in such a way that it is constricted in the surrounding area with constant cross-sectional change cone of the pn-junction and which is shaped and the angle Θ assumes the shape of a truncated pyramid ( German of the level of the pn junction and the cone jacket 20 Auslcgeschrift 1 029 483). between 1 and 10 ° and that the pn over- Corresponding to an older, not to the state of gang lies within the conical zone. Technology related proposal can increase the capacity 2. Electrical capacitor according to claim 1, change of a pn junction as a function of characterized in that the pre-tension applied to the cone is increased, in-shaped Part of the semiconductor body in the direction of that between the transition and one of the ends A further part is connected to the current, whose electrode-located zone of the semiconductor has a continuous cross-sectional area steadily increasing. nuely or gradually decreasing transverse 3. Method for producing an electrical cut is given (German Patent 1 075 745). In all cases mentioned, the semiconductor bodies Proverbs 1 and 2, characterized in that _{3O is provided} with a distribution gradient of the foreign atoms of the semiconductor body made of a monocrystal over the pn junction. is cut, of the foreign semiconductor had by drawing at a the such While up to now in the manufacture of desired distribution gradient the greatest difficulties half atoms of the pn junction corresponding overall conductor devices with constant is obtained exactly vorschwindigkeit, and that he Toggle ₃₅ written characteristics, which is then brought into an electrolytic bath when, as is well known, the indispensable prerequisite for half-inverted voltage is in the η-conductor body, which is to be used in the parametric application of the semiconductor in the immediate vicinity of the strengthening of microwaves , the pn junction stem has a constriction to j _{st it} with the teachings of the present invention erstbilden such that the semiconductor to the p-region _{40 ma} i _s possible, in a simple manner these high out very blunt to one, the pn junction accuracies to achieve, namely in the first comprehensive cone is formed un d of the pn over-line in that the semiconductor body receives the desired areal extension in one go. certain distribution gradients of the foreign atoms 4. The method according to claim 3, characterized in that between the two end faces via the pn junction, _{the desired pn junction is provided during the drawing of the half-45 unc} j _m j _{t of} a certain shape in the area of the conductor monocrystal of the melt will.
Contaminants of the overall o _as equivalent circuit to achieve such a semiconductor Wished distribution gradient of the impurity atoms body showing a variable nonlinear capacitance C in the range of the pn junction overall of a resistor R ₁ is connected in parallel required, whereby speed added. ₅₀ the combination (C, R _v ) is in series with a resistor R _s . For use as a parametric amplifier that responds to very high frequencies, it must then be assumed that the blocking _ layer for the operating frequency ω as a pure dummy 55 resistance behaves, d. H. that the impedance of the non-linear capacitor is approximately ". This