JPH049673A - Semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE:To improve the sensitivity of a sensor by using (m) piezo-resistors allocated in each area out of four areas obtained by diving each beam part of a both-side beam shape to constitute (n) groups of a Wheatstone bridge circuit. CONSTITUTION:Piezo-resistors Ra to Rh are formed in respective areas A to H obtained by dividing the surfaces of respective beam parts 3a, 3b of a both- side beam type semiconductor substrate 2 like crosses on a plane. Three kinds of Wheatstone bridge circuits shown in Table 3 are constituted of these piezo- resistors. Thereby, one-dimensional acceleration FX turns on a switch Sx and is detected by an output VX. Similarly, acceleration Fr turns on a switch Sx and is detected by an output Vx and acceleration FZ turns on a switch SZ and is detected by an output VZ.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a semiconductor acceleration sensor used for detecting acceleration of vehicles, aircraft, buildings, home appliances, etc.

[Conventional technology]

Conventionally, a double-sided beam-shaped two-dimensional semiconductor acceleration sensor shown in FIG. 15 has been proposed.

That is, a semiconductor substrate 1 such as a silicon wafer is subjected to an anisotropic etching process to form a weight portion 2 and a weight portion 2 at the center thereof.
Elastically deformable beam portions 3a, 3b on one opposing side surface of the
A rectangular cutout space 4a is provided on the other opposing side of the weight portion 2.
, 4 b s beam parts 3a, 3b and notch space part 4
Frame portions 5 are formed on the outer sides of each of a and 4b, and the beam portions 3a and 3b form a beam-like structure.

As shown in FIG. 16 (cross-sectional view taken along line II in FIG. 15) and FIG. 17 (partially cutaway perspective view in FIG. 15),
The weight portion 2 and the frame portion 5 are formed to have the same thickness, and the beam portion 3.
a and 3b are formed thinly.

Thus, the X-axis, Y-axis are
When accelerations F 1 , F 2 , FYZ in the axial and Z-axis directions are applied, the stress distribution generated in the beam portions 3a and 3b becomes as shown in FIGS. 18(A) to 18(C).

That is, if tensile stress is expressed as (+) and compressive stress is expressed as (-), (a) When acceleration FX in the X-axis direction is applied, as shown in Fig. 18 (A), the beam part 3a A tensile stress (+) acts on the frame part 5 side, a compressive stress (-) acts on the weight part 2 side, and a tensile stress (+) acts on the weight part 2 side of the beam part 3b, and a tensile stress (+) acts on the frame part 5 side. Compressive stress (-) acts on each.

(b) When the acceleration FY in the y-axis direction is applied, the stress is canceled out on the weight part 2 side and the frame part 5 side in each of the beam parts 3a and 3b, as shown in FIG. 18(B). Tensile stress (+) and compressive stress (-) in the direction act.

(c) When acceleration Fz in the Z-axis direction is applied, as shown in FIG. Compressive stress (-) acts on each side.

Therefore, when accelerations F, FY, and FZ are applied, piezoresistors RRXl'Zl' RR formed by impurity diffusion or ion implantation on the surface of the beam part 3a and impurity diffusion Z2' x on the surface of the beam part 3b.
2 or piezoresistor RR formed by ion implantation etc.
The resistance change of RR is shown in the table x3° z3° z4' x4 1 below.

Table 1 Therefore, as shown in FIG. 19, by configuring a Wheatstone bridge circuit with piezoresistors R and R on one opposite side and piezoresistors Rx2xi x8 and Rx4 on the other side, the Acceleration Fx is detected.

In addition, as shown in FIG. 20, by configuring a Wheatstone bridge circuit with piezoresistors R2□ and R on one opposite side and piezoresistors R2□ and R2, 3 on the other side, it is possible to acceleration Fz is detected.

Therefore, the output x when switches S and S are turned on
Two-dimensional X in the X-axis direction and Z-axis direction by z V ,■
It is possible to detect the acceleration of Z.

Problems to be solved by invention C] As seen in FIG. 18 above, the beam portion 3g.

The stress generated in '3b is the weight part 2 of beam parts 3a and 3b.
The piezoresistance RR-R is maximum near the frame portion 5 (near both ends of the beam portions 3g and 3b).
R-RR・xL'zl' z2″ x2° x
The highest sensitivity can be obtained when each of the 3° z3'RR is placed at the same position z4' x4 .

However, since such an arrangement is physically impossible,
As shown in FIGS. 15 and 16, piezoresistors Rx1 to
Rx4 is placed near both ends of the beams 3a and 3b, and piezoresistors Rzl to Rz4 are placed close to and in parallel inside the beams 3a and 3b (piezoresistors R and The arrangement of R may be x z reversed).

Therefore, there is a problem in that the detection sensitivity of one of the accelerations F 1 and F 2 in the X-axis and Z-axis directions is inferior to the others.

In view of such problems, the present invention aims to obtain a semiconductor acceleration sensor with high detection sensitivity, and focuses on dividing the surfaces of the beam parts 3a and 3b into four equal parts in a plane, and the following This was done based on knowledge.

That is, the beam portion 3a when accelerations F, FY, and Fz are applied to the double-sided beam-shaped semiconductor substrate 1 shown in FIG.
, 3b, as shown in FIG.
, 3b is divided into four equal cross-shaped surfaces 8
Considering two regions A-H, the stress is the 18th
The stress distributions in Figures (A) to (C) are as shown in Table 2 below.

Table 2 From Table 2, we can see that a Wheatstone bridge circuit is constructed using piezoresistors formed in each region, and the combinations of each region for the four sides of the bridge can be extracted by changing the resistance value due to changes in stress in each region. a) In the case of acceleration Fx, a Wheatstone bridge circuit is optimal, with areas (A/10B) and (E+F) as one opposite side, and areas (C+D) and (G+H) as the other opposite side.

(b) For acceleration F, let the areas (A + D) and (F + G) be one opposite side,
A Wheatstone bridge circuit with regions (B + C) and (E + H) as the other opposite sides is optimal.

(c) For acceleration F2, a Wheatstone bridge circuit is optimal, with areas (A + B) and (G + H) as one opposite side, and areas (C + D) and (E + F) as the other opposite side.

It can be recognized that

Then, the piezoresistor placed in the area A-H is
, B, G, H near the frame 5 side, areas C, D,
In E and F, it is possible to form them near the weight part 2 side, and it can be recognized that the resistance value can be changed largely.

Furthermore, for -dimensional acceleration detection, one piezoresistor is installed in each area (total of 8 pieces), and for two-dimensional acceleration detection, two piezoresistors are placed in each area (total of 16 pieces) in parallel above and below. , and for three-dimensional acceleration detection, three in each area (total 24
It can be recognized that piezoresistors (pieces) are formed in parallel above and below.

[Means to solve the problem]

In order to achieve the above object, the present invention is based on the above findings, and provides a double-sided beam-shaped semiconductor acceleration sensor.
m piezoresistors (m + number corresponding to the number of dimensions of the detected acceleration) are formed in each area obtained by dividing the surface of each beam into four equal parts in a cross shape, and the piezoresistors form n sets (n 2) A Wheatstone bridge circuit is constructed, the number of which corresponds to the number of dimensions of acceleration that can be detected when m changes. Furthermore, the piezoresistors are formed near both ends of the beam in each region. Each side of the Wheatstone bridge circuit consists of two piezoresistors of the same dimension in each dimension for acceleration detection formed on each beam part connected in series.

[Effect]

By configuring n sets of Wheatstone bridge circuits using m piezoresistors formed in each area obtained by dividing each beam part of the double-sided beam shape into four, it is possible to calculate -dimensional, two-dimensional, and three-dimensional accelerations. Furthermore, in the case of two dimensions, one-dimensional acceleration can also be detected, and in the case of three dimensions, one-dimensional and two-dimensional acceleration can also be detected by operating a switch of the Wheatstone bridge circuit, if necessary.

〔Example〕

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

(Example 1 - One-dimensional acceleration sensor) As shown in FIG. 1, the surface of each beam part 3a, 3b of the double-sided beam-shaped semiconductor substrate 1 is divided into four equal cross-shaped areas A-H in plan view. Piezoresistors R to Rh are formed inside (total 8
pieces, piezoresistance Ra.

Place the piezo resistors R, R, R, and Rf near the frame portion 5 side g of the beam portions 3a and 3b.
(formed near the weight portion 2 side of the weight portions 3a and 3b, respectively).

Therefore, the accelerations F and F are based on Table 2 above.

Based on the configuration guidelines for Wheatstone bridge circuits for YFz detection, three types of Wheatstone bridge circuits shown in Table 3 below are configured.

Accordingly, the acceleration Fx in the -dimensional direction turns on the switch S and is detected by the output (2).

X
Detected by

Therefore, a Wheatstone bridge circuit (Fig. 2) on each side is constructed by connecting two piezoresistors in series for detecting the acceleration Fx.
, when acceleration FY in the other axis direction is added,
From Table 2 above, the resistance value changes on the (R + Rb) side, (R0 + R) side, (R + R, ) side and (Rg + de Rh) side are 0 in total, and when acceleration Fz is added, (R + R ) x
(R,+Rf)-(Ro+Rd)a b
Since no output is produced due to the relationship e x (R+Rh), there is no sensitivity to acceleration in directions other than the X-axis direction.

Similarly, the Wheatstone bridge circuits shown in FIGS. 3 and 4 have sensitivity only in the Y-axis direction and only in the Z-axis direction.

(Example 2 - Two-dimensional acceleration sensor) As shown in FIG.
';R', R;Ro, R';R'a
a b b c
dR, R, R', R', R, R, R'.

de e f f
g gR' and R are formed vertically in parallel (total h 16 pieces).

Therefore, the accelerations F and F are based on Table 2 above.

Based on the configuration guidelines for Wheatstone bridge circuits for YFz detection, four types of Wheatstone bridge circuits shown in Table 4 below are configured.

Therefore, the two-dimensional acceleration F - F is the acceleration of the switch S
, S is turned on, and the output V, V, 1!
yl X detected.

Similarly, acceleration Fx-F7 in two-dimensional direction is Sui-Sochi S
, S is turned on, and the output v , ■ is used to check
Z
Z is output and acceleration F −FZ is set by switch s,,s
2 is turned on and detected by the output v v .

y2″ 2 The arrangement of the piezoresistors formed in each region is the fifth
As shown in the figure, it is symmetrical with respect to the center line 1-1 of the semiconductor substrate 1 (for example, R3 and R are in one dimension, R'
and R' are resistances corresponding to the detection b a b of the other dimension), but the vertical relationship of R3 and Rb may be reversed.

The two-dimensional acceleration sensor of this embodiment has a switch SX'
It can also be used as a one-dimensional acceleration sensor by turning on Syl'''z alone.

Table 4 (Example 3 - Three-dimensional acceleration sensor) As shown in Fig. 10, piezoresistors R,
R, R, RRR-R.

xa ya za zb'yb'
xb' xcR,R,RRR・R,R.

yc zc zd″ yd'xd' x
e yeRze'Rzf,yf''xi,' R
Xg' p,,,, ``'Zg'l? RR and R, respectively'' are formed in parallel belowzh' yh
'xh (24 total).

Thus, the accelerations F, F, based on Table 2 above.

Based on the configuration guidelines for a port (-) stone bridge circuit for FZ detection, configure a point stone bridge circuit as shown in Table 5 in 1.3.

Table 5 Therefore, the acceleration in the three-dimensional direction Fx to F Y F z is obtained by turning on switches s, sy, and s, and outputting V.

X Z
XV and V are detected.

z The arrangement of the piezoresistors formed in each region is R,
R, R; R, R, R (semiconductor x y z z
y Center line 1 of X body board 1
-1 symmetry), but not limited to R, R,, R,, R, R
, R and R.

3'Z
Z 3'ZR,R,i
;ζ, R, R, etc. total 6 types of sets X yy
There is an XZ combination.

The −1-dimensional acceleration sensor of this embodiment has a switch S,
One-dimensional X by turning on S, S,
yZ acceleration sensor 1. -1 Also switch S, S;S.

Two-dimensional acceleration Z by turning on X y y S, S, S
It can also be used as a ZX degree sensor.

〔Effect of the invention〕

The present invention has the following effect racks.

(a) Piezoresistors for acceleration detection are formed near both ends of the maximum stress in each beam of the double-sided beam.
As a result, sensitivity is significantly improved.

(b) Each side of the Wheatstone bridge circuit has two piezoresistors connected in series, so when acceleration in the other axis direction is applied, the two resistance values change or the total becomes O, and the resistance value changes in the other axis direction. In equation 1, since the products of the resistance values of the opposite sides are equal, it has no sensitivity to acceleration in other axis directions,
A highly accurate acceleration sensor can be provided.

(e) Depending on the number of piezoresistors formed in each area obtained by dividing each beam into four, it is possible to configure -dimensional, two-dimensional, -knee-dimensional, etc. acceleration sensors, and also to configure two-dimensional acceleration sensors. can be used as a one-dimensional acceleration sensor, or as a three-dimensional acceleration sensor, it can be used as a one-dimensional acceleration sensor, a two-dimensional acceleration sensor, and L2, and is highly useful.

[Brief explanation of drawings]

Fig. 1 is a plan view of Embodiment 1 of the present invention, Fig. 2 is a Wheatstone bridge circuit diagram for detecting acceleration in the X-axis direction, and Fig. 3 is a Wheatstone bridge circuit diagram for detecting acceleration in the Y-axis direction. , Fig. 4 is a Wheatstone bridge circuit diagram for detecting acceleration in the Z-axis direction, Fig. 5 is a plan view of the second embodiment, Fig. 6 is a Wheatstone bridge circuit diagram for detecting acceleration in the X-axis direction of the second embodiment, Fig. 7 Figure 8 is a Wheatstone bridge circuit diagram that also detects acceleration in the Y-axis direction. Figure 9 is a Wheatstone bridge circuit diagram that also detects acceleration in the Y-axis direction. , FIG. 10 is a plan view of Embodiment 3, FIG. 11 is a Wheatstone bridge circuit diagram for detecting acceleration in the X-axis direction of Embodiment 3, and FIG. 12 is a Wheatstone bridge circuit diagram for detecting acceleration in the Y-axis direction. Figure 13 is a Wheatstone bridge circuit diagram for Z-axis acceleration detection, and Figure 14 shows the 5.8 areas A by dividing the surface of each beam into four equal parts.
15 is a plan view of a conventional double-sided beam-shaped two-dimensional acceleration sensor, FIG. 16 is a sectional view taken along the line 1-1 in FIG. 15, and FIG. 17 is a
Figure 5 is a partially cutaway perspective view, Figures 18 (A) to (C) are explanatory diagrams of stress generated in the beam, Figure 19 is a Wheatstone bridge circuit diagram for detecting acceleration in the X-axis direction, Figure 20 is a Z-axis diagram. This is a Wheatstone bridge circuit for detecting axial acceleration. DESCRIPTION OF SYMBOLS 1... Semiconductor substrate, 2... Weight part, 3a, 3b...
- Beam parts, 4a, 4b... Notch space parts, 5... Frame parts, Ra~R, R'~R', R-R, R-R. h a h xa x
h ya yhRza~Rzh...Piezo resistance. Applicant's agent Hiroshi Fujimoto Figure 14

Claims (3)

[Claims] 1. In a double-sided beam-shaped semiconductor acceleration sensor, the surface of each beam is divided into four equal cross-shaped areas, and the
(m: the number corresponding to the number of dimensions of the detected acceleration) piezoresistors are formed, and the piezoresistors form n sets (n: the number corresponding to the number of dimensions of the detectable acceleration when m changes) of Wheatstones. A semiconductor acceleration sensor characterized by comprising a bridge circuit. 2. 2. The semiconductor acceleration sensor according to claim 1, wherein the piezoresistors are formed near both side edges of the beam in each region. 3. 3. The semiconductor acceleration sensor according to claim 1, wherein each side of the Wheatstone bridge circuit is connected in series with two piezoresistors of the same dimension in each dimension for acceleration detection formed on each beam.