JP2836846B2 - Semiconductor sensor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor sensor for detecting a physical external force such as acceleration, contact pressure, air pressure, mechanical vibration, and the like.

[Conventional technology]

Conventionally, techniques in such a field include, for example,
The thing shown in 62-121367 is known. In this conventional sensor, a cantilever is formed of silicon oxide (SiO ₂ ) or silicon nitride (Si ₃ N ₄ ) on a semiconductor substrate such as silicon, and a stress detecting element such as a piezoresistive element is formed at the base end. With the provision, the acceleration is electrically detected. There are various materials for the piezoresistive element for detecting the stress. For example, a material made of Si can obtain a sensitivity of about 100 × 10 ⁻¹² cm ² / dyne.

On the other hand, Japanese Patent Application Laid-Open No. 63-18272 discloses an example in which a transistor is incorporated in a semiconductor sensor, and a charge due to a piezoelectric effect is applied to the gate of the transistor to detect an acceleration based on a change in the characteristic. In this sensor, a piezoelectric body and an inertial mass are disposed on a gate oxide film of a MOSFET, and charges are sent to a gate without passing through a lead wire.

[Problems to be solved by the invention]

However, of the above-mentioned prior arts, the former type using the piezoresistive element has a drawback that the detection sensitivity of acceleration or the like is not sufficient. On the other hand, in the latter case, the piezoelectric body and the inertial mass had to be provided on the FET, so that the sensor became large and the cost was high.

Therefore, an object of the present invention is to provide a semiconductor sensor capable of detecting a physical external force such as acceleration, touch pressure, atmospheric pressure, mechanical vibration, or the like with high sensitivity with a simple structure.

[Means for solving the problem]

A semiconductor sensor according to the present invention is formed on a support, a variable member fixed to the support and deformed by a physical external force (acceleration, pressure, etc.), and a portion where the deformation of the variable member occurs. Junction field-effect transistor (J-FE
T), wherein the physical external force is detected by a change in the electrical characteristics of the junction field effect transistor.

[Action]

According to the configuration of the present invention, when the J-FET is deformed,
Stress is generated at the interface between the gate electrode and the channel layer, and polarization appears, and the electrical characteristics such as the threshold value of the J-FET change. Therefore, by knowing the change in the characteristic, it is possible to detect stress due to acceleration, pressure, and the like.

〔Example〕

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a perspective view of the basic configuration of the embodiment. FIG. 1A shows a type for detecting acceleration (cantilever type), and FIG. 1B shows a type for detecting pressure (diaphragm type). I have. In the sensor shown in FIG. 1A, a crystal growth layer 2 made of, for example, gallium arsenide (GaAs) is epitaxially grown on a semiconductor substrate 1 made of, for example, silicon (Si). Then, a part of the semiconductor substrate 1 (the part indicated by the symbol A in the figure) is removed by etching, and the left part in the figure forms a cantilever 3 as a deformable member. A J-FET is formed on the crystal growth layer 2 at the base end of the cantilever 3 by an epitaxial growth method or the like, and this is used for the stress detection FFT 4.
Has made. On the crystal growth layer 2 on the support side (right side in the figure) of the cantilever 3, a signal processing circuit 5 for performing processing such as amplification on the detection signal is formed.

1 (a), when acceleration is applied in the direction of arrow G in the figure, the semiconductor substrate 1 on the cantilever 3 side acts as a weight 1G, and the portion of the crystal growth layer indicated by arrow A (Deformable member) 2 is bent. That is, the stress due to the bending changes the threshold value (V _th ) of the stress detection FET 4 and the like, and thus the above-described acceleration is detected. In order to detect stress by changing the threshold value of the stress detection FET 4, it is necessary to form an inverter by combining with a resistor, for example, and it is necessary to amplify the detection signal. The circuit elements are configured in the signal processing circuit 5.

In the sensor of FIG. 1B, a crystal growth layer 2 is formed on a semiconductor substrate 1 as in FIG. 1A, but a portion A of the semiconductor substrate 1 which is removed by etching is shown in FIG. ) And different. That is, in this embodiment, the semiconductor substrate 1 is removed by etching or the like at the central portion (first portion K ₁ ) of the device to form a deformable member of the crystal growth layer 2, and the second portion K ₂ surrounding it is formed. Semiconductor substrate 1
Are left to form a support for the crystal growth layer (deformable member) 2. Note that the stress detection FET 4 is formed as a J-FET in the crystal growth layer 2 in a portion where stress is generated by pressurization (a portion that becomes a deformable member). Further, a signal processing circuit 5 is separately formed in the crystal growth layer 2 in the portion (support portion) where the semiconductor substrate 1 remains.

The first diagram in the apparatus of (b), for example when pressure is applied in the direction of arrow G, the diaphragm shown in K ₁ is curved upwardly, causing stress. Then, the threshold value or the like of the stress detection FET 4 changes due to the polarization right below the gate region due to the piezoelectric effect. Therefore, for example, by forming an inverter circuit with a resistor in the same manner as in FIG. Can be detected.

Next, the configuration and detection principle of the acceleration sensor according to the present invention will be specifically described with reference to FIGS.

As shown in FIG. 2, a crystal growth layer 2 is formed on an upper surface of a semiconductor substrate 1 by an epitaxial growth method. The semiconductor substrate 1 and the crystal growth layer 2 are removed in a substantially Ω shape, and a central portion is a cantilever 3. Has made. The semiconductor substrate 1 is left at the tip of the cantilever 3 as a deformable member and forms a weight 1G. At the base of the cantilever 3, a stress detection FET 4 made of a J-FET is provided. Is formed. The specific configuration of the stress detection FET 4 is as shown in FIG. 3, but will be described later in detail. Further, a semiconductor resistor R is formed in a portion other than the cantilever 3 of the crystal growth layer 2, and is wired so as to constitute an inverter circuit together with the stress detection FET 4. The specific configuration and operation of this inverter circuit are as shown in FIG. 5, and the description will be given later.

In the specific example described above, when acceleration is applied in the direction of arrow G in the figure, the weight 1G causes the base end of the cantilever 3 to bend, and thus stress appears. Then, the threshold value of the stress detection FET 4 formed by performing epitaxial growth or the like on the compound semiconductor changes at the interface between the gate region below the gate electrode and the channel layer due to polarization by the so-called piezoelectric effect. On the other hand, since no resistance is applied to the resistor R, the resistivity does not change. Therefore, when the voltages V _D and V _I and the ground level are applied from the pad 6 to the inverter circuit including the stress detection FET 4 and the resistor R, the voltage V _O is output. This output voltage V _O is input to the signal processing circuit 5, where predetermined signal processing is performed.

The configuration of the stress detection FET 4 used in the embodiment is
It looks like the figure. The same figure (a) shows the stress detection FET4
FIG. 2B is a plan view of the J-FET, and FIG. 2B is a cross-sectional view taken along line A ₁ -A ₂ . As shown in the figure, an n-type GaAs layer 21 is formed on a crystal growth layer 2 made of semi-insulating GaAs by an epitaxial growth method.
Au / AuGe source electrode 4S and drain electrode 4D
Are formed by, for example, a lift-off method. Gate electrode 4G formed between source electrode 4S and drain electrode 4D
Is the lower titanium (Ti) layer 41 and the upper tungsten (W)
Layer 42 and a P ⁺ -type Ga
It is in ohmic contact with the As layer 22. Since the J-FET has a small increase in gate leakage current due to a temperature rise, excellent temperature characteristics can be realized.

In such a J-FET, when stress is applied in the direction of arrow ST in FIG. 3, the P ⁺ -type GaAs layer 22 below the gate electrode 4G
Shear stress acts on the interface between the n-type GaAs layer 21 and the channel layer, and polarization occurs in the channel layer due to the piezoelectric effect. The change in the electrical characteristics such as the threshold value due to the polarization depends on the stress on the surface of the channel layer.

FIG. 4 shows a change in electrical characteristics due to a change in stress. The horizontal axis is the source-drain voltage V _DS of J-FET, the vertical axis represents the source-drain current I _DS. In a normal state, the VI characteristics are as shown by a solid line, but when tensile stress is applied, they become as shown by a dotted line.

As an example of the change in the electrical characteristics thus obtained, the change in the threshold can be detected by, for example, an inverter circuit as shown in FIG. That applies a voltage V _I to the gate of the J-FET as stress sensing FET 4. Then
The output voltage V _O changes as shown in FIG. 5B depending on the voltage V _I. Here, when the threshold value of the J-FET changes, the output voltage V
The falling point of _O shifts as shown by the arrow in FIG. Therefore, when the input voltage to the gate is set to V _I = V _P , the stress applied to the J-FET can be detected from the change in the output voltage V _O.

If the diaphragm, cantilever, and the like are made of a compound semiconductor as in the embodiment, the stress detection FET 4 can be directly formed in a portion of the compound semiconductor where stress occurs. Here, the circuit formed on the compound semiconductor operates sufficiently even in a high-temperature environment and can perform signal processing at high speed, so that a highly accurate semiconductor sensor with excellent environmental resistance can be provided. Since the signal processing circuit 5 for processing the output signal can be formed in the crystal growth layer 2 made of the same compound semiconductor, the configuration of the semiconductor sensor can be made extremely compact.

Further, the semiconductor sensor of the above embodiment can be manufactured with high accuracy by a very simple manufacturing process. Hereinafter, this situation will be described in detail with reference to FIGS. 6 and 7.

First, a semiconductor substrate 1 made of Si is prepared, and a GaAs crystal growth layer 2 is formed on the upper surface of the semiconductor substrate 1 by an epitaxial growth method. Then, the stress detection FET 4 is formed as shown in FIG. 7 described later, and the signal processing circuit 5 is formed in the crystal growth layer 2 by using an ion implantation method, a lift-off method, etc. (FIG. 6A). . After that, a photoresist film is applied on the entire surface.
The portion to be removed of the semiconductor substrate 1 is opened by applying 10 (FIG. 6B). For this window opening, for example, a known photolithography technique may be used.

Next, the semiconductor substrate 1 is removed from the opening of the photoresist film 10 by etching. Here, when wet etching is used, HF acid is used as an etchant, and when dry etching is used, CF ₄ plasma is used as an etchant. When such an etchant is used, Si is easily removed, while Ga is removed.
As is hardly etched, so that only the portion of the semiconductor substrate 1 indicated by an arrow A can be selectively removed as shown in FIG. 6 (c). Finally, when the photoresist film 10 is removed with acetone or the like, a cantilever structure as shown in FIG. 6D can be realized.

The J-FET (stress detection FET) 4 is manufactured as shown in FIG. First, n-type GaAs and P ⁺ -type Ga are formed on the crystal growth layer 2.
As is epitaxially grown and subjected to mesa etching, as shown in FIG. Next, a gate electrode 4G is formed by a lift-off method (shown in FIG. 3B), and the P ⁺ type GaAs layer 22 'is etched using this as a mask. Then, a gate region 22 is formed only below the gate electrode 4 as shown in FIG. Next, when the source electrode 4S and the drain electrode 4D are formed again by the lift-off method or the like,
-FET is completed.

The present invention is not limited to the above embodiments, and various modifications are possible.

For example, the type of sensor is not limited to a diaphragm or a cantilever, and any type of sensor such as a two-point support or a four-point support may be used as long as it generates stress by pressure, acceleration, and the like and detects this stress. In addition, the support and the deformable member are not limited to semiconductors, but may be alumina or the like. The material forming the stress detection FET 4 is not limited to GaAs, but may be gallium phosphide (GaP), indium phosphide (InP), gallium aluminum arsenide (GaAlAs), or the like. May be.

Further, the signal processing circuit may not be formed integrally on the crystal growth layer, but may be provided on another chip. Further, the present invention is not limited to a circuit for detecting a change in electrical characteristics and an inverter circuit as in the embodiment.

〔The invention's effect〕

As described above in detail, according to the present invention, when a deformation is applied to the compound semiconductor FET, stress is generated at the interface between the gate region and the channel layer below the gate electrode, polarization appears, and the threshold value of the J-FET is increased. Changes. Therefore, the acceleration, the pressure, and the like can be detected by knowing the change in the electric characteristics. This semiconductor sensor has a very simple structure and can detect a physical external force with high sensitivity.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a basic configuration of an embodiment of the present invention, and FIG.
FIG. 3 is a perspective view of a specific example of an acceleration sensor configured according to the present invention, FIG. 3 is a diagram showing a structure of a J-FET used in an embodiment of the present invention, and FIG. 4 is a diagram when a stress is applied to the J-FET. 5 is a characteristic diagram showing a change in VI characteristic of FIG. 5, FIG. 5 is an explanatory diagram of a circuit for detecting a change in threshold value and an operation thereof, and FIGS. 6 and 7 are cross-sectional views showing manufacturing steps of a semiconductor sensor according to the embodiment. is there. 1 ... Semiconductor substrate serving as a support, 1G ... weight 2 ... Crystal growth layer serving as a deformable member, 4 ... Stress detection FET
(J-FET), 4G: gate electrode, 4S: source electrode, 4
D: drain electrode, 5: signal processing circuit, 10: photoresist film.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G01L 1/18 G01P 15/08 H01L 29/84

Claims (1)

(57) [Claims] 1. A supporting member, a deformable member fixed to the supporting member and deformed by a physical external force, and a joining type member formed of a piezoelectric semiconductor and disposed at a portion where the deformable member deforms. A semiconductor sensor, comprising: a field effect transistor, wherein the external force is detected by a change in electrical characteristics of the junction field effect transistor due to deformation of the deformable member.