JPS6328615Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor sensor, and more particularly to a semiconductor sensor capable of detecting temperature and detecting displacement or pressure on the same semiconductor substrate.

Strain gauges that utilize the piezoresistive effect of semiconductors have been widely used because they are highly sensitive and can be made compact. It is attracting attention as a sensor for medical equipment because it is particularly sensitive, small, and reliable. In-vivo pressure gauges and pulse wave meters equipped with small semiconductor strain gauges have been put into practical use.

By the way, body temperature measurement is often important for such biological measurements. When inserted into a living body, the smaller the shape of the sensor, the better; it is inconvenient to measure pressure and temperature with separate sensors. There are many advantages to being able to simultaneously measure local displacement and temperature not only in biological systems but also in mechanical systems.

The present invention uses semiconductor integrated circuit manufacturing technology to incorporate a diffused resistor for detecting elastic strain and a PN junction diode for measuring absolute temperature on the same silicon substrate. Because it uses integrated circuit technology, it is possible to create two types of sensors within a 0.1 mm square.

FIG. 1 is a cross-sectional view of an element for explaining the present invention.
FIG. 2 shows its plan view. 1 in Figure 1 is (100)
An n-type silicon substrate having a surface, 2 a P-type diffused resistor for detecting elastic strain of the substrate, and 3 a diode anode for temperature measurement, which are formed at the same time as the P-type diffused resistor. 4 is a negative type n ⁺ type diffusion region of the diode. 5 is an n ⁺ type diffusion region for connecting an electrode to the substrate 1; As shown in FIG. 2, the P-type diffused resistor 2 is formed to form each side of a square, and the width of the resistor is constant.
The sides of this square are arranged in the <110> direction. 6
is the contact window for attaching the electrode to the resistor. The cathode 4, 4' of the diode consists of four circles of equal size. Then, two diagonally located diode are connected in parallel to form a cathode of one diode. The reason why four circular cathodes are used to create two diodes with the same shape is to ensure that the changes in diode characteristics due to the piezoresistive effect are mutually equal. The anodes of the two diodes are common. The anode of the diode is
It is connected to the substrate through contacts 9.

FIG. 3 is an equivalent circuit diagram of the present invention. The left side of the broken line shows the sensor part on the silicon substrate, and the right side shows the external circuit. The P-type diffused resistor 2 has R ₁ , R ₂ , R ₃ ,
Configure a resistor bridge circuit consisting of R ₄ . 10
to 15 indicate the terminals of the sensor. terminal 10,1
The input voltage E of the bridge is applied between 3 and 3. Terminals 14 and 15 are the outputs of the bridge, and an output voltage ΔV _E proportional to the elastic strain can be obtained. Constant current sources I ₁ and _{I 2} that are supplied to two diodes D ₁ and D 2 are connected to the terminals 11 and ₁₂ . An output voltage ΔV _T proportional to the absolute temperature appears between terminals 11 and 12.

Next, the principle of the present invention will be explained. In FIG. 3, it is assumed that resistors R ₁ and R ₃ are in the <110> direction. If the <110> direction component of the elastic strain of the silicon substrate is e ₁ , the <110> direction component perpendicular to this is e ₂ , and the component perpendicular to the substrate surface is e ₃ , then the change in resistances R ₁ and R ₃ due to strain The rates Δ ₁ and Δ ₃ are Δ ₁ = Δ ₃ = A (e ₁ + e ₂ ) + π ₄₄ C ₄₄ (e ₁ − e ₂ ) + Be ₃ ...(1) Rate of change of resistances R ₂ and R ₄ Δ ₂ , Δ ₄ is given by Δ ₂ =Δ ₄ =A(e ₁ +e ₂ )−π ₄₄ C ₄₄ (e ₁ −e ₂ )+Be ₃ (2). Here, A and B are expressed as A=1/2 {π ₁₁ (C ₁₁ +C ₁₂ ) +π ₁₂ (C ₁₁ +3C ₁₂ )} B=π ₁₁ C ₁₂ +π ₁₂ (C ₁₁ +C ₁₂ ). π ₁₁ , π ₁₂ , π ₄₄ are piezoresistance constants of the P-type diffused resistor, and C ₁₁ , C ₁₂ , C ₄₄ are stiffness constants of silicon.

The bridge output ΔV _E is given by the difference between equations (1) and (2), ΔV _E =E/2π ₄₄ C ₄₄ (e ₁ −e ₂ ) ……(3). In this way, an output voltage proportional to the difference in distortion components can be obtained. For normal uniaxial strain, e ₁
Since the signs of and e ₂ are different, a large output voltage can be obtained. In addition, in this method, since distortion is detected on each side of the bridge, the sensitivity is doubled.

Next, the principle of temperature measurement will be explained. diode
Letting the forward voltages of D ₁ and D ₂ be V ₁ and V ₂ respectively, it can be expressed as V ₁ =kT/qlnI ₁ /Is (4) V ₂ =kT/qlnI ₂ /Is (5). Here, k is the Boltzmann constant, q is the unit charge, T is the absolute temperature, and Is is the saturation current of the diode. It is assumed that the two diodes D ₁ and D ₂ have the same Is. Further, it is assumed that the change in Is due to the elastic strain of the silicon substrate is equal for the two diodes.

The difference ΔV _T between the forward voltages V ₁ and V ₂ of the diode is expressed by the formula
From (4) and (5), ΔV _T =kT/qlnI ₁ /I ₂ ...(6) is given. Therefore, by appropriately selecting the value of the externally connected constant current source, an output voltage proportional to the absolute temperature can be obtained. Changes in diode characteristics due to elastic strain of the silicon substrate do not appear in the output as long as the two diodes are equal. Second
As shown in the figure, by cross-connecting four diodes, the effects of elastic strain can be made equal. In this way, absolute temperature measurements are possible without distortion effects.

In the explanation so far, we have considered the case where a P-type diffused resistor is formed on an n-type substrate, but it is also possible to form an n-type diffused resistor on a P-type substrate. However, in this case, the direction of the diffused resistance needs to be in the <100> direction. Then, the distortion output is given by the following equation instead of equation (3).

ΔV' _E = E/2 (π' ₁₁ - π' ₁₂ ) (C ₁₁ - C ₁₂ ) (e' ₁ - e' ₂ ) ...(7) Here, π' ₁₁ and π' ₁₂ are n-type The piezoresistance constants e′ ₁ and e′ ₂ of the diffused resistance are strain components in the <100> and <010> directions, respectively. When a P-type substrate is used, the output voltage of the temperature sensor is similarly given by equation (6) simply by reversing the polarity of the diode.

As is clear from the above description, the present invention enables an extremely small displacement type sensor for simultaneously detecting pressure and temperature. Sensors according to the invention are particularly useful for simultaneously measuring local displacements and temperatures of biological or mechanical systems or structures.

[Brief explanation of drawings]

FIG. 1, FIG. 2, and FIG. 3 are an element cross-sectional view, an element plan view, and an equivalent circuit diagram, respectively, for explaining the present invention. 1...n-type silicon substrate, 2...P-type diffused resistor, 3...P-type diffused layer, 4,4'...n ⁺ -type diffused layer, 5...n ⁺ -type diffused layer for making substrate contact , 6... contact of diffused resistor, 7... cathode of diode, 8... anode of diode, 9...
Contacts for connecting the substrate and the anode of the diode, R ₁ , R ₂ , R ₃ , R ₄ ... P-type diffused resistor, D ₁ ,
D ₂ ... Diode, 10 ... Common terminal, 11,
12...Diode terminal, 13...Bridge input voltage terminal, 14, 15...Bridge output terminal.

Claims (1)

[Scope of utility model registration request] A bridge circuit including a diffused resistor of one conductivity type formed on one main surface of a semiconductor substrate of another conductivity type, and a bridge circuit formed on one main surface of the semiconductor substrate so as to equally receive elastic strain generated in the semiconductor substrate. a pair of PN junction diodes formed, a means for detecting elastic strain of the semiconductor substrate from the output of the bridge circuit, a pair of current sources each connected to the pair of PN junction diodes and flowing currents of different values; A semiconductor sensor comprising: means for detecting a difference in forward voltage occurring in the PN junction diode.