JP5413802B2 - Strain detector - Google Patents

Description

  The present invention relates to a strain detection element, and more particularly, a transistor type strain detection element having a gate electrode, a source electrode, and a drain electrode, and having a detection sensitivity far superior to that of a metal strain gauge. It relates to an element.

Conventionally, a metal strain gauge is used as an element for detecting strain. The metal strain gauge may be used as a single detection element (sensor) or may be used in a bridge circuit in order to improve detection sensitivity.
In a state where a constant current is applied to the metal strain gauge, the amount of change between the voltage before strain and the voltage after strain is measured, and strain is detected based on the amount of change. Since the metal strain gauge has a small amount of voltage change due to strain, when it is used alone, it cannot detect minute strain.
When a metal strain gauge is used by being incorporated in a bridge circuit, the detection sensitivity is improved, but the entire detection element including the bridge circuit is increased in area and complicated in circuit.

  Conventionally, a transistor having a gate electrode, a source electrode, and a drain electrode is mainly used as a high-frequency, high-output power device, and sufficient detection sensitivity is realized when used as a strain detection element. It ’s hard to say.

JP 2008-277604 A

  The present invention has been made in view of such circumstances, and is a transistor-type strain detection element including a gate electrode, a source electrode, and a drain electrode, and has a detection sensitivity that is far superior to a metal strain gauge. An object of the present invention is to provide a strain detection element having

The first invention is
A strain detection element comprising a gate electrode, a source electrode, a drain electrode, and a layer made of a piezoelectric material in which a channel is formed,
(A) the length of the gate electrode is greater than 2 μm;
(B) the width of the gate electrode is smaller than 1 mm;
(C) the sum of the distance between the gate electrode and the source electrode and the distance between the gate electrode and the drain electrode is greater than 13 μm;
The strain detection element is characterized in that at least one of the three conditions is satisfied.

In the first invention, the “distance between the gate electrode and the source electrode” means the distance between the opposing edges of the gate electrode and the source electrode. The “distance between the gate electrode and the drain electrode” means the distance between the opposing edges of the gate electrode and the drain electrode.
According to the first invention, when at least any one of the three conditions (a) to (c) is satisfied, the detection sensitivity (10 times) that is markedly superior to that of a metal strain gauge. A strain detection element having the above can be obtained.

According to a second invention, in the first invention,
The gate electrode and the electron conductive layer below the gate electrode are bent.

  According to the second invention, in the first invention, when the length of the gate electrode is increased, and when the sum of the distance between the gate electrode and the source electrode and the distance between the gate electrode and the drain electrode is increased, It is possible to prevent the strain detecting element from becoming longer.

According to a third invention, in the second invention,
The layer made of the piezoelectric material is etched in a region other than the lower region between the source electrode and the drain electrode so as not to energize in a region other than the lower region of the gate electrode. A conductive layer is formed.

  According to the third invention, in the second invention, a region other than the lower region is etched so that current does not flow in a region other than the lower region of the gate electrode, and the bent electron conduction layer (electron conduction path) is etched by this etching. ) Is formed. Thus, for example, when the gate electrode is bent so that it is alternately folded at three locations in the opposite direction, the first linear portion from one end of the gate electrode to the first folded portion and the first folded portion to the first folded portion Electricity between the second linear portion from the second folded portion to the second folded portion, the third linear portion from the second folded portion to the third folded portion, and the fourth linear portion from the third folded portion to the other end portion Separation can be performed reliably. Further, the gap (gap) between the first linear portion and the second linear portion, the gap between the second linear portion and the third linear portion, and the third linear portion 203 and the fourth linear portion. Each gap between 204 can be reduced. Therefore, the strain detection element can be configured more compactly. The same applies when there are four or more folded portions.

According to a fourth invention, in the second invention,
The layer made of the piezoelectric material is ion-implanted in a region other than the lower region so as not to pass current between the source electrode and the drain electrode in a region other than the lower region of the gate electrode, and is bent by the ion implantation. The electron conductive layer is formed.

  According to the fourth invention, in the second invention, a region other than the lower region is ion-implanted so that current does not flow in a region other than the lower region of the gate electrode, and this ion implantation causes a bent electron conduction layer (electron). A conduction path) is formed. Thus, for example, when the gate electrode is bent so that it is alternately folded at three locations in the opposite direction, the first linear portion from one end of the gate electrode to the first folded portion and the first folded portion to the first folded portion Electricity between the second linear portion from the second folded portion to the second folded portion, the third linear portion from the second folded portion to the third folded portion, and the fourth linear portion from the third folded portion to the other end portion Separation can be performed reliably. Further, the gap (gap) between the first linear portion and the second linear portion, the gap between the second linear portion and the third linear portion, and the third linear portion 203 and the fourth linear portion. Each gap between 204 can be reduced. Therefore, the strain detection element can be configured more compactly. The same applies when there are four or more folded portions. Further, the mechanical strength of the strain detecting element can be increased as compared with the case of etching as in the third aspect of the invention.

  According to the present invention, it is possible to provide a transistor-type strain detection element including a gate electrode, a source electrode, and a drain electrode, and having a detection sensitivity far superior to that of a metal strain gauge. it can.

The top view which shows the distortion | strain detector based on 1st Embodiment of this invention. 1 is a longitudinal sectional view of the strain detection element shown in FIG. Sectional drawing which shows the distortion detection apparatus containing the distortion detection element shown by FIG. The figure which illustrates the Vgs-vds characteristic of the distortion detection element shown in FIG. The figure which illustrates the change of the Vgs-Vds characteristic when compressive strain or tensile strain is applied to the strain detection element shown in FIG. The figure which illustrates the ΔVgs-ΔVds characteristic when compressive strain or tensile strain is applied to the strain detecting element shown in FIG. The figure which illustrates the relationship between distortion amount (epsilon) and voltage change rate (DELTA) Vds / Vds1 when compressive strain or tensile strain is applied to the strain detection element shown by FIG. Flowchart illustrating a strain detection method using the strain detection element shown in FIG. 1 is a diagram showing the relationship between the voltage change amount ΔVds due to strain and the gate length Lg in the strain detection element shown in FIG. 1 is a diagram illustrating a relationship between a voltage change amount ΔVds due to strain and a gate width Wg in the strain detection element illustrated in FIG. 1 is a diagram illustrating a relationship between a voltage change amount ΔVds due to strain and a sum Lgs + Lgd of distances between electrodes in the strain detection element illustrated in FIG. 1. The top view which shows the distortion | strain detection element concerning 2nd Embodiment of this invention. AA line sectional view showing the strain sensing element shown in FIG. The top view which shows the distortion | strain detection element concerning 3rd Embodiment of this invention. AA line sectional view showing the strain sensing element shown in FIG.

(First embodiment)
A strain detection element according to a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a plan view showing a strain detection element according to the first embodiment. FIG. 2 is a longitudinal sectional view of the strain detecting element shown in FIG. FIG. 3 is a cross-sectional view showing a strain detection apparatus including the strain detection element shown in FIG. FIG. 3 is a diagram illustrating the amount of change in the detection voltage when the length of the gate electrode is adjusted. FIG. 4 is a diagram illustrating a change amount of the detection voltage when the width of the gate electrode is adjusted. FIG. 5 is a diagram illustrating the amount of change in detection voltage when the sum of the distance between the gate electrode and the source electrode and the distance between the gate electrode and the drain electrode is adjusted.

  As shown in FIGS. 1 and 2, the strain detection element 1 according to the first embodiment includes a gate electrode 2, a source electrode 3, a drain electrode 4, and a layer (hereinafter referred to as a piezoelectric material) formed with a channel. , Which is referred to as a piezoelectric material layer). Specifically, the strain detection element 1 includes, for example, a field effect transistor (FET), an insulated gate bipolar transistor (IGBT), a heterostructure field effect transistor (HFET), a modulation-doped field effect transistor (MODFET), It is composed of a high electron mobility transistor (HEMT) or the like. As the piezoelectric material constituting the piezoelectric material layer 5, for example, a III-V group semiconductor such as AlGaN or GaN can be used.

  Hereinafter, the strain detection element 1 using a high electron mobility transistor (HEMT) formed using AlGaN or GaN which is a piezoelectric material will be described as an example, and this embodiment will be described in detail. A strain detection device 6 having the strain detection element 1 will also be described. The first embodiment relates to a strain detection element, a strain detection device, and a strain detection method that can detect compressive strain and tensile strain with high sensitivity.

  The strain detection element 1 includes a substrate 7, a buffer layer 8, a channel layer 9, a carrier supply layer 10, an insulating film 11, a gate electrode 2, a source electrode 3, and a drain electrode 4. It is a mobility transistor.

The substrate 7 is made of sapphire. The buffer layer 8 is made of LT-AlN (low temperature aluminum nitride). The channel layer 9 is made of GaN (gallium nitride) which is a piezoelectric material. The carrier supply layer 10 is made of Al _0.25 Ga _0.75 N (aluminum gallium nitride) that is a piezoelectric material. The channel layer 9 and the carrier supply layer 10 constitute the piezoelectric material layer 5 described above. These are laminated in order.

A source electrode 3 and a drain electrode 4 made of TiA1 (titanium aluminum) are formed on the carrier supply layer 10. A gate electrode 2 made of P-Si (polysilicon) is formed on the carrier supply layer 10 via an insulating film 11 made of SiO ₂ (silicon dioxide). In the strain detection element 1, an electron conductive layer (two-dimensional electron gas = 2DEG) 500 made of a potential well and having extremely high electron mobility is generated near the junction interface between the channel layer 9 and the carrier supply layer 10. The electron conductive layer 500 is an energization path through which the source electrode 3 and the drain electrode 4 are energized.

The greatest feature of the first embodiment is the following configuration. That is,
(A) The length Lg of the gate electrode is larger than 2 μm, (b) the width Wg of the gate electrode is smaller than 1 mm, (c) the distance Lgs between the gate electrode and the source electrode, and the distance Lgd between the gate electrode and the drain electrode. And at least one of the three conditions that the sum Lgs + Lgd is greater than 13 μm is satisfied.
In the following description, the distance Lgs between the gate electrode and the source electrode is the gate-source distance Lgs, the gate electrode-drain distance Lgd is the gate-drain distance Lgd, the gate-source distance Lgs, and the gate-drain electrode. The sum Lgs + Lgd with the distance Lgd may be referred to as the sum Lgs + Lgd of the interelectrode distances.
The reason why the size of each electrode is limited as in the above (a) to (c) will be described later.

  FIG. 3 is a diagram illustrating a schematic configuration of the strain detection device 6 including the strain detection element 1. As a distortion detection method by the distortion detection device 6, the technique of Japanese Patent Application No. 2008-101890 or the technique of Japanese Patent Application No. 2008-166493 previously filed by the present applicant can be used.

  In the present embodiment, when compressive strain or tensile strain is applied, strain is obtained by utilizing a predetermined relationship between the voltage change amount ΔVds between the drain electrode 4 and the source electrode 3 and the strain amount ε. An example of detecting the quantity ε is shown.

  As shown in FIG. 3, the strain detection device 6 includes a strain detection element 1, a voltage detection unit 16, a voltage application unit 12, a strain amount detection unit 14, and a constant current source 15.

  The voltage detection unit 16 has a function of detecting the voltage Vds between the drain electrode 4 and the source electrode 3 (ground) of the strain detection element 1. The voltage detection means 16 includes a storage means (not shown), detects a voltage Vds1 at a certain time point and a voltage Vds2 at another time point, a voltage change amount ΔVds = Vds2−Vds1, a voltage change rate ΔVds / Vds1, etc. It has the function to calculate.

  The distortion amount detection unit 14 is connected to the voltage detection unit 16 and the like, and has a function of detecting the distortion amount ε based on the voltage detected by the voltage detection unit 16 and the like. The voltage detection unit 16 and the distortion amount detection unit 14 are included in, for example, an IC including a CPU, a ROM, a main memory, and the like, and various functions of the voltage detection unit 16 and the distortion amount detection unit 14 are recorded in the ROM or the like. This is realized by reading the program into the main memory and executing it by the CPU. However, part or all of the voltage detection means 16 and the distortion amount detection means 14 may be realized only by hardware. The constant current source 15 has a function of supplying a constant current Ids between the drain electrode 4 and the source electrode 3 of the strain detection element 1. In FIG. 2, the source electrode 3 is grounded.

  FIG. 4 shows the relationship between the voltage Vgs and the voltage Vds in FIG. FIG. 4 is a diagram illustrating the Vgs-vds characteristic of the strain detection element 1 according to this embodiment. In FIG. 4, Vth represents the threshold voltage. FIG. 5 is a diagram illustrating a change in the Vgs-Vds characteristic when compressive strain or tensile strain is applied to the strain detecting element 1. In FIG. 5, the vicinity of the threshold voltage Vth in FIG. 4 is enlarged.

  When compressive strain or tensile strain is applied to the strain detecting element 1 in a direction perpendicular to the thickness direction of the channel layer 9 or the like, polarization due to the piezoelectric effect occurs in the channel layer 9 and the carrier supply layer 10, and FIG. As shown in FIG. 4, the threshold voltage Vth shifts in the negative direction when compressive strain is applied, and the threshold voltage Vth shifts in the positive direction when tensile strain is applied. That is, when compressive strain or tensile strain is applied in a state where the voltage Vgs is constant, the voltage Vds decreases or increases. Further, there is a relationship that the amount of decrease in the voltage Vds increases as the amount of strain due to compressive strain increases, and the amount of increase in the voltage Vds increases as the amount of strain due to tensile strain increases. Therefore, by detecting the voltage Vds, it is possible to detect the amount of strain caused by the applied compressive strain or the amount of strain caused by the tensile strain.

  FIG. 6 is a diagram illustrating the ΔVgs-ΔVds characteristic when compressive strain or tensile strain is applied to the strain detecting element 1. In FIG. 6, the voltage change amount ΔVds is the voltage between the drain electrode 4 and the source electrode 3 before applying the compressive strain or the tensile strain to the strain detecting element 1 Vds1, and the drain electrode 4 when the compressive strain or the tensile strain is applied. ΔVds = Vds2−Vds1 when the voltage between the source electrode 3 and the source electrode 3 is Vds2.

  As shown in FIG. 6, the voltage change amount ΔVds is a function of the voltage Vgs applied between the gate electrode 2 and the source electrode 3. The voltage change amount ΔVds is a characteristic that the absolute value becomes larger as the voltage Vgs approaches the threshold voltage Vth. This indicates that by adjusting the voltage Vgs to be close to the threshold voltage Vth, it is possible to obtain a large gauge factor K and to detect a minute strain.

  FIG. 7 is a diagram illustrating the relationship between the strain amount ε and the voltage change rate ΔVds / Vds1 when compressive strain or tensile strain is applied to the strain detecting element 1. In FIG. 7, ΔVds is the voltage change amount ΔVds = Vds2−Vds1 shown in FIG. ΔVds / Vds1 on the vertical axis represents the voltage change rate. The amount of strain ε on the horizontal axis is the amount of strain when compressive strain or tensile strain is applied, with the negative side corresponding to compressive strain and the positive side corresponding to tensile strain.

  As shown in FIG. 7, when compressive strain is applied, the voltage change rate ΔVds / Vds1 decreases in proportion to the strain amount ε, and when tensile strain is applied, the voltage change rate ΔVds / Vds1 is proportional to the strain amount ε. To increase. The slope of the voltage change rate ΔVds / Vds1 varies depending on the voltage Vgs. Thus, since the voltage change rate ΔVds / Vds1 and the strain amount ε are in a proportional relationship, by adjusting to a predetermined voltage Vgs and obtaining the voltage change rate ΔVds / Vds1 in that state, the compression strain and the tensile strain are increased. The strain amount ε in both directions can be detected.

  FIG. 8 is a flowchart illustrating a distortion detection method according to this embodiment. An example of a method for detecting the amount of distortion will be described with reference to FIG. Note that the strain amount ε can be detected by using, for example, the strain detection device 6 illustrated in FIG.

  First, in step 1, the relationship between the Vgs-ΔVds characteristic illustrated in FIG. 6 and the distortion amount ε using the voltage Vgs as a parameter and the voltage change rate ΔVds / Vds1 as illustrated in FIG. 7 is obtained in advance. (S1). Here, Vds1 is a detected value of the voltage Vds in a state where no distortion is applied, and ΔVds is Vds2−Vds1 when a detected value of the voltage Vds in a state where the strain is applied is Vds2.

  Next, in step 2, based on the Vgs-ΔVds characteristic (for example, FIG. 6) obtained in advance in step 1, the voltage applying unit 12 adjusts the voltage Vgs to a value near the threshold voltage Vth. For example, in the case of the Vgs-ΔVds characteristic illustrated in FIG. 6, for example, the voltage Vgs is adjusted to around −25 [V] (S2). Thereafter, the adjustment value of the voltage Vgs is kept constant until the distortion amount ε is obtained in step 5 described later.

  Next, in step 3, the voltage Vds is detected by the voltage detection means 13 in a state where no distortion is applied (S3). The detected value of the voltage Vds at this time is Vds1. Next, at step 303, a strain to be measured (compression strain or tensile strain) is applied, the voltage detection means 16 detects the voltage Vds (the detected value of the voltage Vds at this time is Vds2), and the voltage change amount ΔVds. = Vds2-Vds1 is calculated (S4).

  Next, at step 5, the voltage change rate ΔVds / Vds 1 is calculated by the voltage detection means 16. Then, the distortion amount detection means 14 determines the distortion amount ε to be measured based on the relationship (for example, FIG. 7) between the distortion amount ε using the voltage Vgs obtained in advance in step 1 as a parameter and the voltage change rate ΔVds / Vds1. Obtain (S5). As described above, the strain amount ε can be obtained by utilizing the predetermined relationship between the voltage change rate ΔVds / Vds1 and the strain amount ε.

  According to this embodiment, compressive strain or tensile strain is applied to the strain detection element 1 having the gate electrode 2, the source electrode 3, the drain electrode 4, and the layer 5 made of a piezoelectric material in which a channel is formed. And the voltage Vds between the drain electrode 4 and the source electrode 3 changes, and there is a predetermined relationship between the voltage change rate ΔVds / Vds1 and the strain amount ε caused by compressive strain or tensile strain. The corresponding distortion amount ε can be obtained by calculating the voltage change rate ΔVds / Vds1. At this time, since the voltage Vgs is adjusted to a value in the vicinity of the threshold voltage Vth, the strain amount ε can be obtained with a high gauge factor, so that a minute strain can be detected.

  Further, the strain amount ε can be obtained by measuring only the voltages Vds1 and Vds2 without measuring the change in resistance value when the strain to be measured is applied. As a result, for example, it is not necessary to detect a minute change in resistance value with a high accuracy using a bridge circuit, which is a high accuracy measurement circuit, and the distortion amount ε can be detected more easily than in the past. .

Next, the reason why the size of each electrode is limited as in the above (a) to (c) will be described.
The voltage change amount ΔVds due to distortion is given by the following equation (Equation 1).

  The meaning of each character in the equation (Equation 1) is as shown in the following equation (Equation 2).

The equation (Equation 1) is derived.
The source-drain resistance Rds is expressed by the following equation (Equation 3).

  The source-drain voltage Vds ′ when the gate voltage is applied is expressed by the following equation (Equation 4).

  When strain is applied, the 2DEG concentrations n and n ′ increase by Δn, and the source-drain voltage Vds ″ is expressed by the following equation (Equation 5).

  From the equations (Equation 4) and (Equation 5), the change amount ΔVds of the source-drain voltage due to the applied strain is expressed by the following equation (Equation 6), and the equation (Equation 1) is derived.

  Solving the equation (Equation 1) for the gate length Lg yields the following equation (Equation 7). This equation shows the relationship between the voltage change amount ΔVds due to distortion and the gate length Lg.

  Solving the equation (Equation 1) for the gate width Wg yields the following equation (Equation 8). This equation shows the relationship between the voltage change amount ΔVds due to distortion and the gate width Wg.

  When the equation (Equation 1) is solved for the sum Lgs + Lgd of the interelectrode distance, the following equation (Equation 9) is obtained. This equation shows the relationship between the voltage change amount ΔVds due to distortion and the sum Lgs + Lgd of the interelectrode distance.

FIG. 9 is a graph showing the relationship between the voltage change amount ΔVds due to the distortion expressed by the equation (Equation 7) and the gate length Lg. As can be seen from FIG. 9, as the gate length Lg increases, the absolute value of the voltage change amount ΔVds also increases monotonously. Conventionally, the transistor is designed with the gate length Lg set to 2 μm or less. However, in this embodiment, the transistor is designed with the gate length Lg set to a value larger than 2 μm. In the example shown in FIG. 9, the gate width Wg is set to 1 mm, and the sum Lgs + Lgd between the electrodes is set to 13 μm.
It has been confirmed that the voltage change amount ΔVds when the gate length Lg is set to a value larger than 2 μm is 10 times or more the voltage change amount ΔVds of the metal strain gauge.

FIG. 10 is a graph showing the relationship between the voltage change amount ΔVds due to distortion and the gate width Wg expressed by the equation (Equation 8). As can be seen from FIG. 10, the absolute value of the voltage change amount ΔVds monotonously decreases as the gate width Wg increases. Conventionally, the transistor is designed with the gate width Wg set to 1 mm or more. However, in this embodiment, the transistor is designed with the gate width Wg set to less than 1 mm. In the example shown in FIG. 10, the gate length Lg is set to 2 μm, and the sum Lgs + Lgd between the electrodes is set to 13 μm.
It has been confirmed that the voltage change amount ΔVds when the gate width Wg is set to less than 1 mm is 10 times or more the voltage change amount ΔVds of the metal strain gauge.

FIG. 11 is a graph showing the relationship between the voltage change amount ΔVds due to the distortion expressed by the equation (Equation 9) and the sum Lgs + Lgd of the inter-electrode distances. As can be seen from FIG. 11, as the sum Lgs + Lgd of the interelectrode distances increases, the absolute value of the voltage change amount ΔVds also increases monotonously. Conventionally, the transistor is designed with the sum Lgs + Lgd of the distance between the electrodes set to 13 μm or less. However, in this embodiment, the transistor is designed with the sum Lgs + Lgd of the distance between the electrodes set to a value larger than 13 μm. In the example shown in FIG. 11, the gate length Lg is set to 2 μm and the gate width Wg is set to 1 mm.
It has been confirmed that the voltage change amount ΔVds when the sum Lgs + Lgd of the distance between the electrodes is set to a value larger than 13 μm is 10 times or more the voltage change amount ΔVds of the metal strain gauge.

  Therefore, as described above, (a) the length of the gate electrode is larger than 2 μm, (b) the width of the gate electrode is smaller than 1 mm, (c) the distance between the gate electrode and the source electrode, When at least one of the three conditions that the sum of the distance between the gate electrode and the drain electrode is greater than 13 μm is satisfied, the voltage change amount ΔVds is the voltage change of the metal strain gauge. It becomes 10 times or more of the amount ΔVds.

  In addition, it is preferable that any two conditions are satisfy | filled among the three conditions of said (a)-(c), and it is more preferable that all three conditions are satisfy | filled.

  The voltage change amount ΔVds of the strain detection element 1 according to the present embodiment is specifically shown to be 10 times or more the voltage change amount ΔVds of the metal strain gauge. In the following example, the case where the strain ε = 1 (μm) is detected when the current Ids = 1 (A) is applied is shown. In this case, the absolute value of the voltage change amount ΔVds of the strain detection element 1 according to the present embodiment is 3.42 (mV) or more. The absolute value of the voltage change amount ΔVds of the metal strain gauge is 240 (μV). Therefore, the absolute value of the voltage change amount ΔVds of the strain detection element 1 according to the present embodiment is 10 times or more than the absolute value of the voltage change amount ΔVds of the metal strain gauge. Therefore, the strain detection element 1 according to the present embodiment can detect strain much more sensitively than the metal strain gauge.

  The numerical value of the design range of the strain detection element 1 according to the present embodiment is substituted into the above equation (Equation 1). The gate length Lg> 2 μm, the gate width Wg <1 mm, and the interelectrode distance sum Lgs + Lgd> 13 μm. The values shown in the following formula (Equation 10) are substituted for other parameters.

  Then, the voltage change amount ΔVds is expressed by the equation (Equation 11).

  Therefore, the absolute value of the voltage change amount ΔVds due to distortion is expressed by the equation (Equation 12). The voltage change amount ΔVds is a negative value for compressive strain and a positive value for tensile strain. Therefore, the absolute value of the voltage change amount ΔVds is calculated.

Next, the voltage change amount ΔVds of the metal strain gauge is calculated.
Assuming that the current maximum gauge factor K of the metal strain gauge is 2.1 and the resistance R is 120 (Ω), the metal strain gauge is used alone. When the strain 1 (μstrain) is calculated from the voltage change amount when the current I is 1 (A), the voltage change amount ΔV is expressed by the following equation (Equation 13).

  From the equations (Equation 12) and (Equation 13), it can be seen that the absolute value of the voltage change amount ΔVds of the strain detecting element 1 according to the present embodiment is 10 times or more the voltage change amount ΔV of the metal strain gauge. .

  Next, the difference in voltage change ΔVds and the difference in element area when the gate length Lg, the gate-source distance Lgs, and the gate-drain distance Lgd are a times and the gate width Wg is 1 / a times will be discussed.

  First, the difference in the voltage change amount ΔVds will be examined. Before the gate length Lg, the gate-source distance Lgs, and the gate-drain distance Lgd are multiplied by a, ΔVds is expressed by the following equation (Formula 14).

  After the gate length Lg, the gate-source distance Lgs, and the gate-drain distance Lgd are multiplied by a, ΔVds is expressed by the following equation (Equation 15).

As can be seen from the equations (Equation 14) and (Equation 15), it can be seen that the voltage change amount ΔVds becomes a ² times after the multiplication by a, and the voltage change amount ΔVds increases remarkably.

  Next, the difference in element area will be examined. Before the gate length Lg, the gate-source distance Lgs, and the gate-drain distance Lgd are multiplied by a, the element area S is expressed by the following equation (Equation 16).

  After the gate length Lg, the gate-source distance Lgs, and the gate-drain distance Lgd are multiplied by a, ΔVds is expressed by the following equation (Equation 17).

  As can be seen from the equations (16) and (17), after a times, the element area S is 1 / (Wg · Ls) (source electrode area) and Wg · Ld (drain electrode area). It turns out that it becomes a times and an element area becomes remarkably small.

  As described above, according to the first embodiment, since at least any one of the three conditions (a) to (c) is satisfied, it is remarkably superior to a metal strain gauge. In addition, a strain detecting element having a high detection sensitivity (10 times or more) can be obtained.

(Second Embodiment)
A strain detection element according to a second embodiment of the present invention will be described with reference to the drawings. FIG. 12 is a plan view showing a strain detection element according to the second embodiment. FIG. 13 is a cross-sectional view taken along line AA showing the strain detection element shown in FIG. In FIG. 13, a region outside the source electrode and a region outside the drain electrode are not shown. In the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and the description thereof is omitted.

  The strain detection element 100 according to the second embodiment is different from the first embodiment in that the gate electrode 2 is formed in a straight line in the first embodiment, whereas the gate electrode 20 and the gate electrode in the second embodiment. 20 is that the electron conduction layer (energization path) 501 below is bent (see FIG. 12).

  The bending method is not particularly limited. For example, as shown in FIG. 12, the gate electrode may be bent so that it is alternately folded in the opposite direction. Specifically, the gate electrode may have a U-shaped bent portion at a plurality of locations. In the example shown in FIG. 12, U-shaped bent portions in opposite directions are alternately formed.

  When the gate length is increased and the sum of the distance between the electrodes is increased by bending the gate electrode and the electron conductive layer (energization path) 501 below the gate electrode 20, the strain detection element Can be prevented from becoming longer.

  In the example shown in FIG. 13, the layer 5 made of the piezoelectric material is etched between the source electrode 3 and the drain electrode 4 in a region other than the lower region so as not to pass current in a region other than the lower region of the gate electrode 20. Yes. The etched area is indicated by reference numeral 50. By this etching, a bent electron conductive layer (energization path) 501 is formed.

  As a result, when the gate electrode is bent so as to be alternately folded in the opposite direction, the first linear portion 201 from one end of the gate electrode 20 to the first folded portion and the second folded portion from the first folded portion. Between the second linear portion 202 up to the second folded portion, the third linear portion 203 from the second folded portion to the third folded portion, and the fourth linear portion 204 from the third folded portion to the other end portion. Electrical separation can be reliably performed. Further, the gap (gap) between the first linear portion 201 and the second linear portion 202, the gap between the second linear portion 202 and the third linear portion 203, and the third linear portion 203 and the first linear portion 203 The gaps between the four straight portions 204 can be reduced. Therefore, the strain detection element can be configured more compactly. The same applies when there are four or more folded portions.

(Third embodiment)
A strain detection element according to a third embodiment of the present invention will be described with reference to the drawings. FIG. 14 is a plan view showing a strain detection element according to the third embodiment. FIG. 15 is a cross-sectional view taken along the line AA showing the strain detection element shown in FIG. In FIG. 15, illustration of the region outside the source electrode and the region outside the drain electrode is omitted. In the third embodiment, the same components as those of the second embodiment are denoted by the same reference numerals, and the description thereof is omitted.

In the second embodiment, the region other than the lower region is etched so as not to energize the region other than the lower region of the gate electrode 20.
On the other hand, in the strain detection element 110 according to the third embodiment, the layer 5 made of the piezoelectric material is arranged below the source electrode 3 and the drain electrode 4 so as not to be energized in a region other than the region below the gate electrode 20. A region other than the region is ion-implanted (see FIG. 15). An ion implantation region is indicated by reference numeral 60. By this ion implantation, a bent electron conductive layer (energization path) 502 is formed.

  Thereby, when the gate electrode 20 is bent so as to be alternately folded in the opposite direction, the first linear portion 201 from one end of the gate electrode 20 to the first folded portion and the second folded portion to the second Between the second linear portion 202 from the folded portion, the third linear portion 203 from the second folded portion to the third folded portion, and the fourth linear portion 204 from the third folded portion to the other end portion Can be reliably separated. Further, the gap (gap) between the first linear portion 201 and the second linear portion 202, the gap between the second linear portion 202 and the third linear portion 203, and the third linear portion 203 and the first linear portion 203 The gaps between the four straight portions 204 can be reduced. Therefore, the strain detection element can be configured more compactly. The same applies when there are four or more folded portions. Further, the mechanical strength of the strain detection element can be increased as compared with the case of etching as in the second embodiment.

  The present invention can be used for a transistor-type strain detecting element including a gate electrode, a source electrode, and a drain electrode.

DESCRIPTION OF SYMBOLS 1,100,110 Strain detection element 2,20 Gate electrode 3 Source electrode 4 Drain electrode 5 Layer made of piezoelectric material 6 Strain detector 7 Substrate 8 Buffer layer 9 Channel layer 10 Carrier supply layer 11 Insulating film 12 Voltage application means 14 Strain Quantity detection means 15 Constant current source 16 Voltage detection means 50 Etching area 60 Ion implantation area

Claims (3)

A strain detection element comprising a gate electrode, a source electrode, a drain electrode, and a layer made of a piezoelectric material in which a channel is formed,
(A) the length of the gate electrode is greater than 2 μm;
(B) the width of the gate electrode is smaller than 1 mm;
(C) the sum of the distance between the gate electrode and the source electrode and the distance between the gate electrode and the drain electrode is greater than 13 μm;
At least one of the three conditions is satisfied ,
The strain detecting element, wherein the gate electrode and the electron conductive layer below the gate electrode are bent . The layer made of the piezoelectric material is etched in a region other than the lower region between the source electrode and the drain electrode so as not to energize in a region other than the lower region of the gate electrode. The strain detection element according to claim 1, wherein a conductive layer is formed. The layer made of the piezoelectric material is ion-implanted in a region other than the lower region between the source electrode and the drain electrode so as not to energize in a region other than the lower region of the gate electrode, and is bent by this ion implantation. The strain detection element according to claim 1, wherein the electron conductive layer is formed.

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