JPH077013B2 - Semiconductor sensor - Google Patents

Description

The present invention relates to a semiconductor sensor for detecting acceleration, contact pressure, atmospheric pressure, mechanical vibration and the like.

[Conventional technology]

Conventionally, as a technique in such a field, for example, JP-A-62-62
The thing shown in the -121367 gazette 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 detection element such as a piezoresistive element is formed at the base end. By being provided, the acceleration is electrically detected. There are various kinds of materials for the piezoresistive element for detecting the stress, and 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 Laid-Open No. 63-18272 discloses, for example, a device in which a transistor is incorporated in a semiconductor sensor and an electric charge due to a piezoelectric effect is applied to the gate of the transistor to detect the acceleration based on a change in the characteristics of the transistor. In this sensor, a piezoelectric body and an inertial mass body are arranged on the gate oxide film of the MOSFET so that electric charges can be sent to the gate without passing through a lead wire.

[Problems to be Solved by the Invention]

However, of the above-mentioned conventional techniques, the former type that uses a piezoresistive element for detection has a drawback that the detection sensitivity for acceleration and the like is not sufficient. On the other hand, in the latter case, the piezoelectric body and the inertial mass body must be provided on the FET, so the sensor becomes large and the cost becomes high.

Therefore, the present invention provides a highly sensitive acceleration with a simple structure,
An object of the present invention is to provide a semiconductor sensor capable of detecting touch pressure, atmospheric pressure, mechanical vibration, and the like.

[Means for Solving the Problems]

The semiconductor sensor according to the present invention is formed on a support, a deformable member fixed to the support and deformable by a physical external force (acceleration, pressure, etc.), and a portion where the deformable member is deformed. Compound semiconductor field effect transistor (FE
T), and the physical external force is detected by the change in the threshold value of the field effect transistor.

Here, in the semiconductor sensor, the gate electrode of the field effect transistor is formed on the channel layer made of a compound semiconductor, and the channel layer is not separated from the channel layer even when the deformable member is deformed. A first metal layer that is in close contact with the first metal layer and a first metal layer that is formed on the first metal layer and has a high Young's modulus that causes stress in the channel layer when the deformable member is deformed. It is characterized by comprising two metal layers.

Further, the deformable member is characterized by having a laminated structure of GaAs and GaAlAs.

[Action]

According to the configuration of the present invention, when the FET of the compound semiconductor is deformed, stress is generated at the interface between the gate electrode and the channel layer, polarization appears, and the threshold voltage of the FET changes. Therefore, by knowing the change in this threshold value, acceleration, pressure, etc. can be detected.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a perspective view of the basic configuration of the embodiment, and FIG. 1A shows a type (cantilever type) for detecting acceleration,
FIG. 3B shows a type (diaphragm type) for detecting pressure. 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 (portion indicated by symbol A in the figure) is removed by etching, and the left side portion in the figure forms a cantilever 3 as a deformable member. A Schottky gate field effect transistor (MESFET) is formed in the crystal growth layer 2 at the base end portion of the cantilever 3 by an ion implantation method or the like, which constitutes a stress detection FET 4. A signal processing circuit 5 for performing processing such as amplification on the detection signal is formed on the crystal growth layer 2 on the support body side (right side in the drawing) of the cantilever 3.

In the device of FIG. 1 (a), when acceleration is applied in the direction of arrow G in the drawing, the semiconductor substrate 1 on the cantilever 3 side has a weight.
It acts as 1 G, and the crystal growth layer (deformable member) 2 in the portion indicated by arrow A bends. Then, the stress due to this bending changes the threshold value (V _th ) of the stress detection FET 4, and thus the above acceleration is detected. In order to detect stress by changing the threshold of the stress detection FET4, it is necessary to form an inverter by combining it with a resistor, for example, and it is also necessary to amplify the detection signal. The elements are arranged in the signal processing circuit 5.

In the sensor of FIG. 1B, the crystal growth layer 2 is formed on the semiconductor substrate 1 as in the case of FIG. 1A, but the portion A removed by etching of the semiconductor substrate 1 is shown in FIG. )
Is different from That is, in this embodiment, the semiconductor substrate 1 is removed by etching or the like in the central portion (first portion K ₁ ) of the device to form a deformable member composed of the crystal growth layer 2 and the second portion K ₂ surrounding it. Thus, the semiconductor substrate 1 remains and forms a support for the crystal growth layer (deformable member) 2. The stress detection FET 4 is formed as a MESFET in the crystal growth layer 2 in a portion where stress is generated by pressurization (a portion that becomes a deformable member). Further, the crystal growth layer 2 in the portion (support portion) where the semiconductor substrate 1 remains
A signal processing circuit 5 is separately formed in the.

In the apparatus of FIG. 1 (b), when pressure is applied, for example, in the direction of arrow G, the diaphragm indicated by K ₁ bends upward, causing stress. Then, since the threshold value of the stress detection FET 4 changes due to the polarization immediately below the gate due to the piezoelectric effect, the above pressure can be quantitatively detected by forming an inverter circuit with a resistor as in the case of FIG. 1A, for example. You can

Next, the configuration and the detection principle of the acceleration sensor constructed 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 the upper surface of the 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 the central portion is a cantilever beam 3. Is doing. The semiconductor substrate 1 is left at the tip of the cantilever 3 as a deformable member to form a weight 1G, and the stress detecting FET 4 made of MESFET is formed at the base of the cantilever 3. . This stress detection FET4
The specific configuration of is as shown in FIG. 3 and the change in stress is as shown in FIG. 4, but a detailed description will be given later. Further, a semiconductor resistor R is formed on a portion of the crystal growth layer 2 other than the cantilever 3 and is wired so as to form 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 thereof will be given later.

In the above specific example, when acceleration is applied in the direction of arrow G in the figure, the weight 1G causes the base end portion of the cantilever 3 to bend, thus causing stress. Then, in the stress detection FET 4 formed by performing ion implantation or the like on the compound semiconductor, the threshold value changes at the interface between the gate electrode and the channel layer due to polarization due to the so-called voltage effect. On the other hand, since the resistance R is not stressed, the resistivity does not change. Therefore, the voltage V _D , V _{1 is} applied from the pad 6 to the inverter circuit composed of the stress detection FET 4 and the resistor R.
And when the earth level is applied, the voltage V _O is output.
The output voltage V _O is input to the signal processing circuit 5, where it is subjected to predetermined signal processing.

The structure of the stress detection FET 4 used in the embodiment is as shown in FIG. FIG. 3A is a plan view of the MESFET forming the stress detection FET 4, and FIG. 3B is a sectional view taken along the line A ₁ -A ₂ . As shown, an n-type GaAs layer 21 is formed in the crystal growth layer 2 made of semi-insulating GaAs by ion implantation or the like,
A source electrode 4S and a drain electrode 4D made of, for example, Au / AuGe as ohmic metal are formed on both sides thereof by a lift-off method, for example. The gate electrode 4G formed between the source electrode 4S and the drain electrode 4D is composed of a lower titanium (Ti) layer 41 and an upper tungsten (W) layer 42,
The gate length is L _g and the gate electrode height is H _g .

In such a MESFET, when stress is applied in the direction of the arrow ST in FIG. 3, shear stress acts on the interface between the gate electrode 4G and the channel layer of the n-type GsAs layer 21, and the channel effect is polarized by the piezoelectric effect. Occurs. The change in threshold value due to this polarization depends on the stress on the surface of the channel layer, as shown in FIG.

Here, in order to effectively operate the MESFET having the above structure as the stress detection FET 4, it is desirable to have the following features. First, the smaller the gate length L _g , the higher the sensitivity. That is, as shown in FIG. 4, a gate length L _g of about 0.8 μm provides twice or more sensitivity as compared with a gate length L _{g of} about 1.8 μm. Secondly, the higher the adhesion between the gate electrode 4G and the channel layer of the n-type GaAs layer 21, the more suitable it is to be used as the stress detection FET 4. In order to improve this adhesion, the lower layer 41 of the gate electrode 4G is formed as described above.
Ti with a thickness of about 500Å may be used. Thirdly, the higher the Young's modulus of the gate electrode 4G is, the more polarization can be generated on the surface of the channel layer. In order to obtain such a high Young's modulus, as described above, the upper layer 42 of the gate electrode 4G has a thickness W (4.1 × 10 ¹² dyn / cm ² ) of about 3000 Å.
Can be used. It is also possible to use TiW, TiW silicide, and W silicide. Further, the shear stress applied to the channel layer may be increased by increasing the height H _g of the gate electrode 4G.

The change in the threshold value thus obtained can be detected by, for example, an inverter circuit as shown in FIG. That is,
Voltage V _I is applied to the gate of MESFET as stress detection FET4. Then, the output voltage V _O changes as shown in FIG. 5 (b) depending on the voltage V _I. Here, when the threshold value of the MESFET changes, the falling point of the output voltage V _O shifts as shown by the arrow in FIG. 5 (b). Therefore, the input voltage to the gate V _I = V _P
When set to, the stress applied to the MESFET can be detected from the change in the output voltage V _O.

If the diaphragm, the cantilever, and the like are made of a compound semiconductor as in the embodiment, the stress detection FET 4 can be directly formed in the stress-occurring portion of the compound semiconductor. Here, the circuit formed in the compound semiconductor can sufficiently operate even in a high temperature environment and can perform signal processing at high speed, so that a highly accurate semiconductor sensor having excellent environment 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 structure of the semiconductor sensor can be made extremely compact.

Further, the semiconductor sensor of the above-mentioned embodiment can be manufactured with high precision by an extremely simple manufacturing process. Hereinafter, this situation will be specifically described with reference to FIG.

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 and the signal processing circuit 5
Are formed in the crystal growth layer 2 by an ion implantation method, a lift-off method, or the like (shown in FIG. 6A). Then, a photoresist film 10 is applied on the entire surface to open a portion of the semiconductor substrate 1 to be removed (shown in FIG. 6 (b)). For this windowing, 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 the wet etching method is used, an HF-based acid is used as the etchant, and when the dry etching method is used, CF ₄ plasma is used as the etchant. With such an etchant, Si is easily removed, while Ga is
As is hardly etched, so that only the semiconductor substrate 1 in the portion indicated by arrow A can be selectively removed as shown in FIG. 6 (c). Finally, by removing the photoresist film 10 by ascent or the like, a cantilever structure as shown in FIG. 6 (d) can be realized.

The present invention is not limited to the above embodiment, and various modifications can be made.

For example, the FET as the stress detection FET 4 may be as shown in FIG. In the figure (a), semi-insulating GaAs
An n-type GaAs layer 21 is formed in a mesa shape on the crystal growth layer 2 made of, and a gate electrode 4G, a source electrode 4S, and a drain electrode 4D are formed on the n-type GaAs layer 21 to form a MESFET. In FIG. 2B, n ^{+ is} added to the crystal growth layer 2 made of semi-insulating GaAs.
Ohmic contact layers 22 and 23 made of type GaAs are formed, and a source electrode 4S and a drain electrode 4D are formed thereon. An i-type GaAlAs layer is formed between the source electrode 4S and the drain electrode 4D, and the gate electrode is formed on the i-type GaAlAs layer.
4G is formed, which constitutes a so-called MISFET. The type of sensor is not limited to a diaphragm or a cantilever, and any type such as two-point support or four-point support may be used as long as it is a type that causes stress due to pressure, acceleration, etc. and detects this stress. Also, the support and the deformable member are not limited to semiconductors,
Alumina or the like may be used, and 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.

Furthermore, the signal processing circuit does not have to be integrally formed on the crystal growth layer, and can be provided on another chip.
Further, the circuit for detecting the change in the threshold value is not limited to the inverter circuit as in the embodiment.

〔The invention's effect〕

As described above in detail, in the present invention, the compound semiconductor
When the FET is deformed, stress is generated at the interface between the gate electrode and the channel layer, polarization appears, and the threshold value of the FET changes. Therefore, by knowing the change in this threshold value, acceleration, pressure, etc. can be detected. This semiconductor sensor has an extremely simple structure and can detect a physical external force with high sensitivity.

[Brief description of drawings]

FIG. 1 is a perspective view showing a basic configuration of an embodiment of the present invention, FIG. 2 is a perspective view of a concrete example of an acceleration sensor constructed according to the present invention, and FIG. 3 is used for an embodiment of the present invention. MESFET
FIG. 4 is a characteristic diagram showing a change in threshold value due to stress applied to MESFET, FIG. 5 is a circuit diagram for detecting a change in threshold value, and FIG. 6 is an explanatory view of the action, and FIG. FIG. 7 is a sectional view showing the manufacturing process of the semiconductor sensor, and FIG. 7 is a sectional view showing the structure of another FET applicable to the present invention. DESCRIPTION OF SYMBOLS 1 ... Semiconductor substrate used as a support, 1G ... Weight, 2 ... Crystal growth layer used as a deformable member, 4 ... Stress detection FET, 4G ... Gate electrode, 4S ... Source electrode, 4D ... Drain electrode, 5 ... Signal processing Circuit, 10 ... Photoresist film.

Claims (4)

[Claims] 1. A support, a deformable member fixed to the support and deformable by a physical external force, and a compound semiconductor field effect transistor formed in a portion where the deformable member is deformed. A semiconductor sensor for detecting the external force by changing the threshold value of the field effect transistor, wherein the gate electrode of the field effect transistor is formed on a channel layer made of the compound semiconductor, and the deformable member is deformed. A first metal layer that is in close contact with the channel layer to such an extent that it does not separate from the channel layer even when it occurs, and when the deformable member formed on the first metal layer deforms A semiconductor sensor comprising a second metal layer made of a material having a high Young's modulus that causes stress in the channel layer. 2. The semiconductor sensor according to claim 1, wherein the first metal layer is made of Ti. 3. A support, a deformable member fixed to the support and deformable by a physical external force, and a compound semiconductor field effect transistor formed in a portion where the deformable member is deformed. A semiconductor sensor, comprising: the deformable member having a laminated structure of CaAs and GaAlAs, wherein the semiconductor sensor detects the external force by changing a threshold value of the field effect transistor. 4. The variable shape member comprises a semiconductor crystal growth layer fixedly provided on the support, and the semiconductor crystal growth layer amplifies a detection signal based on a change in resistivity of the semiconductor resistor. The semiconductor sensor according to claim 1 or 3, wherein a circuit is formed.