Semiconductor pressure sensor

• US 5,289,721 A
• Filed: 09/09/1991
• Issued: 03/01/1994
• Est. Priority Date: 09/10/1990
• Status: Expired due to Term

• Current Assignee: Nippondenso Co., Ltd. (DENSO Corporation)
• Original Assignee: Nippondenso Co., Ltd. (DENSO Corporation)
• Inventors: Okada, Hiroshi, Fukada, Tsuyoshi, Tanizawa, Yukihiko, Ikeda, Kazuhisa
• Primary Examiner(s): WOODIEL, DONALD
• Application Number:
  US07/756,223
• Time in Patent Office: 904 Days
• Field of Search: 73/720, 73/721, 73/726, 73/727, 73/754, 73/DIG. 4, 73/708, 73/706, 73/777, 338/4, 338/42, 29/621.1
• US Class Current: 73/727
• CPC Class Codes: G01L 9/0042 Constructional details associated with semiconductive diaphragm sensors, e.g. etching, or constructional details of non-semiconductive diaphragms details about the integration or bonding of piezoresistor in or on the diaphragm G01L9/0052 and G01L9/0057 respectively
• CPC Class Codes: G01L 9/0054 integral with a semiconducting diaphragm
• CPC Class Codes: Y10T 29/49103 Strain gauge making

Abstract

A semiconductor pressure sensor comprises a silicon substrate having a surface orientation of substantially (110), a diaphragm formed from the substrate, strain gauges disposed on the diaphragm, and a base joined with the substrate. The diaphragm has an octagonal shape whose sides are orthogonal to axis<100>, <110>, and<111>, respectively. This sensor causes substantially no output error and no fluctuation between output characteristics of the strain gauges irrespective of a change in temperature.

Claims

1. A semiconductor pressure sensor comprising a silicon substrate having a surface orientation of substantially (110), a diaphragm formed from the substrate, strain gauges disposed on the diaphragm, and a base joined with the substrate, wherein the diaphragm is defined by a concave portion which is anisotropically etched in said substrate, a bottom portion of which having an octagonal shape whose sides are orthogonal to axis<

100>

,<

110>

, and<

111>

, respectively.

2. A semiconductor pressure sensor according to claim 1, wherein the substrate and base have different thermal expansion coefficients.

3. A semiconductor pressure sensor according to claim 1, wherein the principal plane of the substrate has an off-angle of several degrees with respect to a plane (110).

4. A semiconductor pressure sensor according to claim 1, wherein the strain gauges disposed on the diaphragm are connected to form a bridge circuit.

5. A semiconductor pressure sensor according to claim 1, wherein the strain gauges are arranged symmetrically with respect to an axis<

110>

extending through the center of the diaphragm, such that longitudinal axis of the strain gauges are oriented parallel with the axis<

110>

.

6. A semiconductor pressure sensor according to claim 1, wherein the octagonal recessed shape of the diaphragm has a pair of first sides each having a length of l and a pair of parallel second sides spaced apart from each other by a distance L and extending approximately perpendicular to the first sides, wherein l/L is in a range of 0.25 to 0.65.

7. A semiconductor pressure sensor according to claim 6, wherein l/L is around 0.4.

8. A semiconductor pressure sensor according to claim 1, wherein the strain gauges are made of polysilicon resistors.

9. A semiconductor pressure sensor according to claim 1, wherein the substrate comprises a first substrate having a surface orientation of (110) and a second monocrystalline silicon substrate having a surface orientation of (100), the first and second substrates being joined with each other.

10. A pressure sensor as in claim 1 wherein said strain gauges are in a central portion of said diaphragm.

11. A pressure sensor as in claim 1 wherein said sides forming said octagonal shape include two parallel sides orthogonal to the<

111>

axis and substantially vertical to the bottom surface of the cavity, and the remaining sidewalls inclined by a certain number of degrees with respect to the bottom surface of the cavity.

12. A semiconductor pressure sensor comprising a silicon substrate having a surface orientation of substantially (100), a diaphragm formed from the substrate, strain gauges disposed on the diaphragm, and a base joined with the substrate, wherein the diaphragm has an octagonal recessed shape whose sides are orthogonal to axes<

100>

,<

110>

, and<

111>

, respectively, said octagonal recessed shape of the diaphragm including a pair of first sides each having a length of l and a pair of parallel second sides spaced apart from each other by a distance L and extending orthogonally to the first sides, wherein l/L is in a range of 0 to 0.5.

13. A pressure sensor as in claim 12 wherein said sides forming said octagonal shape include two parallel sides orthogonal to the<

111>

axis and substantially vertical to the bottom surface of the cavity, and the remaining sidewalls inclined by a certain number of degrees with respect to the bottom surface of the cavity.

14. A semiconductor pressure sensor comprising an octagonal diaphragm formed by anisotropically etching a semiconductor substrate whose principal plane has a predetermined off-angle with respect to one of the (110) and (100) planes of the semiconductor substrate, a plurality of strain gauges symmetrically arranged on the diaphragm, and a base joined with the substrate, wherein a center of symmetry of the arrangement of strain gauges is at a same position as a center of the bottom of the diaphragm in a direction orthogonal to the principal plane.

15. A semiconductor pressure sensor according to claim 14, wherein a polygonal shape formed on an etching start surface of the substrate is asymmetric when turned half a round, and the octagonal diaphragm is symmetric when turned half a round.

16. A pressure sensor as in claim 14 wherein said sides forming said octagonal shape include two parallel sides orthogonal to the<

111>

axis and substantially vertical to the bottom surface of the cavity, and the remaining sidewalls inclined by a certain number of degrees with respect to the bottom surface of the cavity.