FI71198B - HALVLEDAROMVANDLARE FOER SPAENNINGSMAETARE - Google Patents

Description

1 71198

This invention relates to the manufacture of semiconductor measuring devices, and more particularly to semiconductor voltage sensors for measuring thermal, power and mechanical parameters such as forces, pressures, displacements, accelerations, etc.

A semiconductor voltage sensor is already known, which contains a sensitive part such as a single crystal silicon wafer, which is of the n-conductivity type. Stress transducers are provided on the plate by diffusing the receiving impurity to that plate. The strain gages are isolated from each other by p-n junctions formed during diffusion. The voltage sensors are connected to each other as a bridge or differential, voltage-sensitive circuit whose output signal is proportional to the parameter to be measured, such as pressure. In addition to the parameter to be measured, the temperature of the output signal of the voltage-sensitive circuit is affected, which causes a certain error in the measurements. To take care of this error, the voltage sensor is equipped with a individually adjustable electronic circuit for temperature compensation of the output signal.

The stress sensor under consideration is only able to operate at temperatures below 120 ° C because the silicon p-n junctions lose their insulating properties at higher temperatures.

In addition, this sensor has a relatively low sensitivity because the supply voltage, which is proportional to the output signal, is limited by the value of the breakdown voltage U1 of the p-n junction, which is normally only a few volts.

It should further be noted that existing individually adjustable circuits do not provide the required conversion accuracy for temperature ranges greater than 120 ° C. This is due to the fact that the output signal of the strain gauge interpreter device is strongly and non-linearly dependent on the operating temperature (which in turn is due to the fact that the electrical parameters of semiconductor strain gauges, including silicon strain gauges, are temperature dependent). The existing semiconductor materials used to make the voltage sensors are such that the output signal from a voltage-sensitive circuit containing such a voltage sensor is never completely independent of temperature.

10 A certain sensitive part (stress sensor) for a stress sensor device is already known. This part is made of silicon carbide with a nitrogen content of 7.3 · 10 ^ cm ^ and has stable stress measurement characteristics at temperatures up to 800 ° C.

However, the resistance of the above silicon carbide at the above nitrogen content is significantly dependent on the temperature, which indicates the temperature instability of the output signal.

The sensitive part under consideration is a single tension sensor, which should be attached to a flexible part of the tension sensor device, however, there is hysteresis and creep in the adhesive layer.

A semiconductor pressure measuring transducer is already known, which includes a sensitive part which is a single crystal sapphire substrate 25 having epitaxial stress sensors made of a single crystal silicon film of p-type conductivity. The voltage sensors are connected together as a voltage-sensitive bridge circuit, the output of which is connected to the input of the signal conversion unit. Stress transducers are made of silicon membrane with a resistance value of the order of 0.005 to 0.009 19 ohms · cm, which corresponds to its orifice concentration: p = 3.2 · 10 + 19 -3 1.4 · 10 cm. Such a sensor is free from the disadvantages that exist in the presence of a p-n junction.

However, the voltage sensors that make up the bridge circuit 35 have different temperature resistance coefficients, as a result of which the zero value imbalance voltage across the bridge strongly depends on the temperature, which affects the accuracy of the conversion.

In addition, the output signal of the voltage sensor device in question is also strongly temperature-dependent. In order to guarantee a high measuring accuracy, the sensor must be equipped with a complex, individually adjustable temperature compensation circuit. However, such a circuit is a factor that limits the operating temperature range, and in the 10 cases under consideration, this range is only 20-42 ° C.

It is a primary object of the present invention to provide a semiconductor voltage sensor having voltage sensors of a semiconductor material such that it makes the signal of the output of a voltage sensitive circuit independent of the ambient temperature over a wide temperature range.

The above object is achieved by providing a semiconductor voltage sensor consisting of a sensitive part operated by a monocrystalline sapphire substrate with epitaxial silicon voltage sensors made of 20 p-conductivity silicon connected to each other as a bridge or differential voltage sensitive circuit whose output is connected to a characterized according to the present invention in that the concentration of the openings in silicon is between 3.5 · 19 20 -3 25 10 '- 3 · Ϊ0ζυ cm -3.

If a DC power supply is used to supply current to a voltage-sensitive circuit, it is preferable that the concentration of the holes 19 -3 in silicon is (3.5 to 9) 10 cm

If a DC voltage source is used for the power supply of a voltage-sensitive circuit, it is preferred that the concentration of the openings in the silicon is between (1.8 and 3) 10 cm

A voltage measuring transducer of simple construction is able to guarantee accurate measurements over a wide range of positive and negative temperatures if the sapphire vessel 35, on which there is a voltage-sensitive circuit fed from a DC source, is equipped with an additional voltage 4 71198 supplied with this sensitive circuit from a DC voltage source; the outputs of each voltage-sensitive circuit should be connected to the input of a signal conversion unit via a relay-type switching section, the control circuit of which includes 5 epitaxial silicon thermistors with an aperture concentration of 3.5-10 -3-10 cm, with the thermistor either in the unstressed area and / or in a direction insensitive to the tension of the sapphire substrate.

The semiconductor voltage sensor 10 of the present invention has a number of advantages over conventional sensors. It features improved conversion accuracy and a much wider operating temperature range from -200 to + 200 ° C. The output signal of the voltage-sensitive circuit is independent of temperature, which makes it possible to omit the electronic temperature compensation circuit and, as a result, the sensor is characterized by a simple signal conversion circuit.

Other objects and advantages of the present invention will become more apparent upon consideration of the following detailed description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings, in which:

Figure 1 is a cross-sectional view of a semiconductor pressure sensor in accordance with the present invention.

Figure 2 is a top view of the sensor of Figure 1.

Fig. 3 is a circuit diagram of a stress sensor device showing bridge connection of stress sensors in accordance with the present invention.

Fig. 4 is a diagram illustrating the temperature coefficient of the resistance of p-type silicon films placed on a sapphire compared to a specific resistance.

Fig. 5 is a schematic representation of the total value of the temperature coefficient of resistance and the coefficient of stress sensitivity of silicon films on a p-type sapphire as a function of resistivity.

Figure 6 is a diagram of the temperature coefficient of the meter coefficient of p-type silicon films placed on a sapphire compared to the resistivity.

5 71 198

Figure 7 is a side view of a sensitive portion of a semiconductor pressure sensor in accordance with the present invention, including two voltage sensitive circuits.

Figure 8 is a top view of the sensor of Figure 7.

Figure 9 is a block diagram of the sensor of Figures 7 and 8.

Figure 10 is a graphical representation of the relative change in resistance value in a thermistor as a function of temperature.

Fig. 11 is a pattern representation of the output signals of voltage-sensitive circuits and the adjusted switching section as a function of the heat-10 state.

Figures 1 and 2 show an embodiment of the present invention for which there is a pressure sensor including a cylindrical main body 1, which is on one side of the connection pipe 2 which is intended for pressure P in import. Attached to the opposite side of the body 1 by any known method, such as soldering, is a sensitive part 3. The latter includes a sapphire substrate 4 having a membrane with a bulge in its circumferential portion and epitaxial silicon strain gauges 5 arranged in parallel pairs with the membrane. edge and perpendicular to the radial direction of this film. The orientation of the 4-level crystal structure of the sapphire substrate is (1012). The epitaxial silicon stress transducers 5 are arranged in the silicon crystal plane (100) and are oriented in the directions 25 (011) and (0Ϊ1), the stress transducers 5 having contact surface points 6.

The stress sensors 6 are connected together as a bridge circuit shown in Fig. 3. One diagonal direction of this bridge is connected to a power supply unit 7, which has either a DC supply i or a DC voltage supply UQ. The second diagonal of this bridge acts as an output from a voltage sensitive circuit and is connected to the input of the signal conversion unit 8.

The semiconductor pressure sensor according to the invention operates in the following manner. When power is applied to the bridge circuit and when there is no pressure P acting, the diaphragm 4 is not stressed, so that the resistance value 71198 of the stress sensors 5 is kept at its original level and the output signal of the balanced bridge is zero. When the pressure P is applied to the film 4, the sapphire substrate bends and distorts the silicon stress sensors 5. The deformation changes the resistance value H of the gauges 5, whereby the sign of the change in the resistance value is determined from the direction of the gauges 5 compared to the radius of the film 4.

The dependence between the resistance value R of the stress sensor 5 and the temperature T and the stress £ can be expressed as follows: R (T, £) = R (T) / 1 + K (T) £ 7, (1) where K (T) is stress sensor factor. If the DC voltage 15 Uq is applied to the bridge circuit, the output signal U of this bridge can be expressed as a function: U (T, £) = UQK (T) £; (2) 20 If a direct current i is applied to this bridge circuit, the output signal of the bridge is as follows: U (T, £) = iQR (T) K (T) £. (2 ') 25 The voltage of the stress sensor is proportional to the measurable parameter S, which in this case is the pressure P, thus t = A (T) S. (3) 30 As a result, the output signal can be read: U (T, S) = UK (T) A (T) S (4) o 35 if a DC voltage UQ is applied to the bridge circuit and can be read: 7 71198 U (T, S) = i R (T) K (T) A (T) S (4 ') if a direct current i is applied to the bridge circuit.

In order to make the output signal independent of temperature 5, the following conditions must be satisfied: 1 tfU _.

u 5T 0 / 1,110 * 10 _L_ <TKJT) + _1__ ^ a (t) = K (T) $ TA (T) 4 T υ 'if a direct voltage is applied to the bridge circuit and can be stated: 1 $ R (T) 1 6K (T) _1__ <AND (T) = R (T) §TK (T), 5T A (T) $ fu '' 20 if direct current is applied to the bridge circuit.

The temperature coefficient of the resistance value of the voltage sensors is 1 ÄR (T) OCr = and is the temperature coefficient of the meter coefficient 1 £ k (T) O ^ k = k ~ (T7 4 ~ t ~ 'the temperature coefficient of the elastic conversion of the voltage sensor measuring device is ac ^ = - ^ ye ~ - -, jol-25 I created equations (5) and (5 ') can be written in the form «k + = 0 (6) and also 30 +« k + «k = ° · (6'>

Given that «k is normally small in value, the conditions that must be satisfied in order for the signal of output 35 to be independent of temperature from the bridge circuit can be expressed in the following form: 71198 8

Take «O (?) If the DC voltage is applied to the bridge circuit and can say 5« R + <\ «0 (7 *) if the DC circuit is supplied with direct current. Equations (6), (6 ') and (7), (7') similarly apply to the case where the stress sensors are included in the differential circuit.

The properties of the monocrystalline silicon film (sos) grown on a sapphire substrate differ greatly from the properties of large silicon crystals grown from melt or silicon obtained by diffusion or autoepitaxial growth. The silicon film on the sapphire is strongly compressed due to different coefficients of thermal expansion in silicon and sapphire. Due to the piezoelectric phenomenon caused by the compression of this film, the mixture shifts from the initial operating point of the stress transducer initially used in the stress transducer when it is made of diffused or autoepitaxial silicon. This displacement changes the measurement coefficient K = AR / R £ and it changes the temperature-state coefficient GC ^ of the measurement coefficient, because this displacement depends on the temperature-25 children.

In addition, the piezoelectric phenomenon caused by the compression of the silicon film on the sapphire with heat also changes the resistance amount of the sos voltage sensor compared to silicon without tension. It also changes the value of the ice-50 nity sensor «R, keeping in mind that the compression with heat depends on the temperature. Thus, the monocrystalline silicon film on the sapphire substrate and OC 2 differ from the corresponding values for large, diffused or autoepitaxial silicon.

The strain gauges 5 of the pressure gauges of Figs. Fig. 4 is a diagram of the temperature coefficient of resistance value (G1) for a monocrystalline silicon film on a sapphire substrate compared to a resistance value f at different temperatures T. This diagram shows that the temperature coefficient of resistance of voltage sensors varies only slightly over a wide temperature range and is only slightly dependent on the amount of resistance of the epitaxial silicon film. At the above-mentioned aperture concentration of 10, the inevitable differences in the resistance values of the individual stress sensors have little effect on the temperature coefficients of the resistance amount. As a result, the zero-point imbalance voltage in the bridge is virtually independent of temperature. Moreover, at the above-mentioned aperture concentration, the effect of saturation of the receiving impurity in this silicon improves the uniformity of electrical properties in the epitaxial layer, which further reduces differences in individual resistance transducer resistances and makes the zero unevenness-20 weight even less temperature dependent.

According to an alternative embodiment, the strain gauges of the pressure gauges of Figures 1 and 2 comprise 5 boron-extracted silicon films on a sapphire substrate, in which the concentration of openings in silicon is (3.5 to 9) 10 cm, which corresponds to f = 0.0045 to 0.002 ohms. -senttimetriä. The direct current i is applied to a voltage-sensitive bridge circuit (Fig. 3). In this case, the condition to be satisfied in order to ensure temperature stability at the outlet mark can be described by Equation (6 '). Fig. 5 is a graph of the total value of the temperature coefficient of resistance and the temperature coefficient of the meter coefficient for monocrystalline p-type silicon films on a sapphire substrate compared to the resistance amount $ of these films. The diagram in Figure 5 makes it clear that the dependence 35 (6 *) is realized in a selected range of resistance values over a wide temperature range, i.e. at least between -100 and + 200 ° C, and that the voltage sensitive circuit output signal 10 71198 is independent of temperature in this range (dashed line 9 in Figure 9). 11).

According to another alternative embodiment of the pressure sensor of Figures 1 and 2, the stress sensors comprise 5 boron-treated silicon films on a sapphire substrate, where the concentration of 20 -3 orifices in silicon is (1.8 to 3) 10 cm, which corresponds to a resistance value of 0.0009 to 0.0006 ohms · centimeters and applying a DC voltage UQ (Fig. 3) to this voltage sensitive bridge circuit. In this case, the condition for temperature-10 biosity in the output sign can be described by Equation (6). Fig. 6 is a diagram of the temperature coefficient of the meter coefficient on a p-type silicon film on a sapphire substrate compared to the resistance amount S of this film. As can be seen from this diagram, for the selected resistance range, situation 15 (6) is practically implemented over a wide range of temperatures below zero between at least -200 ° C, so that in this range the output signal is almost independent of temperature (dotted line 10 in Figure 11). .

An alternative embodiment of a tension sensor according to the present invention is shown in Figures 7 and 8.

The latter embodiment includes a metal film 11 integral with the body 12, which includes a cavity into which pressure P is applied (the pipe connection 25 intended to apply pressure to this cavity is not shown in Fig. 7). By any known method, such as, for example, by soldering, a sapphire substrate 13 is attached to the film 11, which is cut along its crystal plane (1012). The substrate 13 has epitaxial strain gauges 14 of boron-hand-irradiated silicon film, with an aperture concentration of 19 -3 (3.5-9) 10 cm. The stress sensors 14 are arranged on the edge of the film 11 and oriented in the crystal directions (110) and (Ϊ10) in this silicon, said stress sensors 14 are arranged in pairs so that the second stress sensor 35 of a pair is parallel to the film 11 radius, while the second sensor is perpendicular to this film. 11 relative to the radius. The tension sensors 14 are connected together

II

il 71198 as a bridge circuit I with contact areas 15. Formed on the surface of the substrate 13 using the optional boron diffusion method, there are epitaxial stress sensors 16 made of boron-treated silicon film, 20 -3 5 where the concentration of openings is (1.8 - 3) 10 cm . Like the gauges 14, the strain gauges 16 are arranged on the edge of the film 11 and are directed in the crystal directions (110) and (110). They are arranged in pairs so that one sensor 16 from a certain pair is parallel to the radius of the membrane 11, while the other sensor 16 from this pair is located perpendicular to the radius of this membrane 11. The voltage sensor 16 is connected to the bridge circuit II with its contact areas 17. An epitaxial thermistor 18 with its contact areas 19 is further placed on the base 13.

The thermistor 18 is made of a boron-treated silicon film, where the concentration of the openings is between 3.5 * 10 20-3 3-10 cm. In the embodiment under consideration, the thermistor 18 is arranged in a stress-free area of the substrate 13 above the side wall of this body 12. The thermistor 18 may also be directed in the stress-insensitive direction of the sapphire substrate 13.

The function of the DC voltage supply source 20 is to supply the DC voltage Uq to the bridge circuit II (Fig. 9). The function of the direct current supply source 21 is to supply direct current iQ to a voltage-sensitive bridge circuit I. These values Uo and 25 iQ are chosen so that at a certain temperature t in the range -100 to 0 ° C (e.g. at t = 50 ° C) and at a certain pressure P the magnitudes of the symbols from the voltage sensitive circuits I and II are equal to each other, i.e. Uj (P) = Outputs from the voltage sensitive

30 of the circuits I and II are connected to the inputs of a regulated, relay-type switching part 22, which part may be an alternator. The output from the switching section 22 is connected to the signal conversion to the input of the unit 23. The control circuit of the switching part 22 includes a thermistor 18. The resistance value 35 R (t) of the thermistor 18 is selected so that it, e.g. at t = -50 ° C

is the response value R (t) = R. where R is the amount of resistance by which the second stable state of the coupling part 22 is caused to change to another.

12 71198

The semiconductor pressure sensor of Figures 7, 8 and 9 operates as follows.

The pressure P (Fig. 7) is applied to the membrane 11. The sapphire base 13 bends with the membrane 11. The silicon voltage sensors 14 and 16 are energized so as to generate output signals U (iP) and Ujj (P) to the outputs of the voltage-sensitive circuits I and II, respectively. At temperatures below zero, such as in the range of -200 to -50 ° C, the amount of resistance R (t) 10 of the thermistor 18 is less than Rq (Fig. 10). As a result, the situation of the switching section 22 is such that the output signal (P) of the voltage-sensitive circuit II is input to the input of the signal conversion unit 23. This symbol U ^ iP) is independent of the temperature at which the above-mentioned temperature range is 15a (curve 10 in Fig. 11). When the point t = -50 ° C is reached, the amount of resistance of the thermistor 18 is equal to Rq (Fig. 10) so that the state of the switching section 22 suddenly becomes opposite and the output of the voltage sensitive circuit I is connected to the input of the signal conversion unit 23.

20 This Uj (P) mark is independent of the temperature in the operating range between e.g. -50 and + 200 ° C (curve 9 in Fig. 11). In the latter temperature range, the resistance value of the thermistor 18 is greater than Rq (Fig. 10) so that a stable state of the switching section 22 is maintained. When the temperature then decreases, the situation of the coupling part 22 changes again when R (t) = R, i.e. at the temperature t = -50 C.

Thus, the signal of the output of the switching part 22 is independent of the temperature in the entire operating range of temperatures (solid line 24 in Fig. 11), i.e.:

UT (P) between -50 ° C and + 200 ° C

U (P) I o o

U (P) between -200UC ^ t ^ -50UC

Claims (4)

13 71198 A semiconductor voltage sensor comprising a sensitive portion having a monocrystalline sapphire substrate with epitaxial voltage sensors made of p-type silicon connected as a bridge or a differential voltage sensitive circuit, the output of which is connected to the input of a signal conversion unit, known as the concentration of silicon is between 10 3.5 * 10 -3 * 10 cm Voltage sensor according to Claim 1, in which the power supply for the voltage-sensitive circuit is a direct current source, characterized in that the concentration of the openings in the silicon is 3.5 · 1019 to 9 · 1019 cm 3. Voltage sensor according to Claim 1, in which the power supply for the voltage-sensitive circuit is a direct voltage supply, characterized in that the concentration of the openings in the silicon is 1.8 · 10 to 3 · 1020 cm -1. Voltage sensor according to Claim 2, characterized in that the sapphire substrate (13) has an additional voltage-sensitive circuit (II) as claimed in claim 3, the outputs of both voltage-sensitive circuits (I and II) being connected to the input of the signal conversion unit (23). via a controlled relay-type coupling portion (22), the control circuit of which includes a silicon epitaxial thermistor (18) having an aperture concentration of 19 20 -3 to 3.5 10 -3 to 10 cm, said thermistor (18) being located either in a stress-free zone, or being oriented in a direction insensitive to the tension of the sapphire substrate (13).