Silicon sensing structure to detect through-plane motion in a plane of material with thermal expansion substantially different from that of silicon
A pressure transducer is provided that has a transducer body with a rim, a diaphragm that deflects in response to pressure and a sensor bonded to the diaphragm at the rim and at a center of the diaphragm. The sensor detects deflection of the metal diaphragm. The sensor and diaphragm are made of different materials. A thermal expansion difference between the sensor and the diaphragm is accommodated by flexures in the sensor that accept relative motion in a radial direction of the metal diaphragm with little effect on a sensitivity of the silicon structure to motion in an axial direction of the diaphragm.
1. A pressure transducer, comprising:
a transducer body with a rim;
a diaphragm having a thickness that is less than a thickness of the rim, the diaphragm having a central pillar that is coplanar with a shelf of the rim;
a sensor bonded at the central pillar and the rim with the bonds being rigid and non-rotating, the sensor extending from the rim to the pillar, wherein pressure-induced deflection of the diaphragm induces double-bending in the sensor with an inner end bending down and an outer end bending up, the sensor including an accommodation structure that provides accommodation in a change of length of the sensor in response to temperature changes and a resulting length change in a body of the sensor; and
one or more piezoresistors in the bending areas that produce equal and opposite resistance changes that can be detected in a Wheatstone bridge.
2. The pressure transducer of claim 1 , wherein the accommodation structure is one or more thin free standing structures within the sensor.
3. The pressure transducer of claim 2 , wherein the thin free standing structures are blades.
4. The pressure transducer of claim 1 , wherein the sensor produces a signal in response to displacement of one sensor end relative to an opposing sensor end.
5. The pressure transducer of claim 1 , wherein the sensor is made of a material selected from at least one of, Si, silicon on oxide and silicon carbide.
6. The pressure transducer of claim 1 , wherein the diaphragm is made of a material selected from at least one of, metals, corrosion-resistant metals and ceramics.
7. The pressure transducer of claim 1 , wherein diaphragm is made of crystalline alumina and supporting structures are polycrystalline.
8. The pressure transducer of claim 1 , wherein a change of temperature in the pressure transducer results in a difference between an unstressed length of the sensor and a radial distance on the diaphragm between a location where the sensor is bonded at a center of the diaphragm and where the sensor is bonded at the rim.
9. The pressure transducer of claim 1 , wherein the one or more piezoresistors positioned in bending areas of the sensor to produce equal and opposite resistance changes.
10. The pressure transducer of claim 9 , wherein the bending areas with the piezoresistors are made soft by making the piezoresistors sufficiently thin to provide that even though a folding or bellowing effect of the sensor accommodating an expansion difference bend in response to pressure-induced deflection, a majority of the bending occurs in bending areas under the piezoresistors.
11. The pressure transducer of claim 1 , further comprising:
one or more flexible structures and gages to measure flexing of the flexible structures.
12. The pressure transducer of claim 1 , wherein parallel slots are etched through a (110) Si wafer that forms a silicon sensor, masked on both sides of the wafer with vertical (111) walls in the wafer.
13. The pressure transducer of claim 1 , wherein a thermal expansion difference between the sensor and the diaphragm is accommodated by flexures in the sensor that accept relative motion in a radial direction of the metal diaphragm with little effect on a sensitivity of the silicon structure to motion in an axial direction of the diaphragm.
14. A pressure transducer, comprising:
a transducer body with a rim;
a diaphragm with a central pillar that is coplanar with a shelf of the rim;
a sensor with a center portion, the sensor being bonded at the central pillar and the rim with the bonds being rigid and non-rotating, the sensor including an accommodation structure positioned at an inflection point to provide accommodate in a change of length of the sensor in response to thermal mismatch, the sensor extending from the rim to the pillar and pressure-induced deflection at a center of the diaphragm induces a distortion of the sensor with a geometry that approximates or is an S-shape, the sensor being bent in an upward direction away from the diaphragm at the rim, and bent in a downward direction towards the diaphragm at the center portion with the inflection point of neutral bending between the rim and the center portion; and
one or more piezoresistors in the bending areas.
15. The pressure transducer of claim 14 , wherein at the inflection point the accommodation structure has little effect on bending at either end of the sensor.
16. The pressure transducer of claim 15 , wherein the accommodation structure is one or more thin free standing structures within the sensor.
17. The pressure transducer of claim 16 , wherein the thin free standing structures are blades.
18. The pressure transducer of claim 14 , wherein the sensor produces a signal in response to displacement of one sensor end relative to an opposing sensor end.
19. The pressure transducer of claim 14 , wherein the sensor is made of a material selected from at least one of, Si, silicon on oxide and silicon carbide.
20. The pressure transducer of claim 14 , wherein the diaphragm is made of a material selected from at least one of, metals, corrosion-resistant metals and ceramics.
21. The pressure transducer of claim 14 , wherein diaphragm is made of crystalline alumina and supporting structures are polycrystalline.
22. The pressure transducer of claim 14 , wherein a change of temperature in the pressure transducer results in a difference between an unstressed length of the sensor and a radial distance on the diaphragm between a location where the sensor is bonded at a center of the diaphragm and where the sensor is bonded at the rim.
23. The pressure transducer of claim 14 , wherein the one or more piezoresistors positioned in bending areas of the sensor to produce equal and opposite resistance changes.
24. The pressure transducer of claim 14 , further comprising:
one or more flexible structures and gages to measure flexing of the flexible structures.
25. The pressure transducer of claim 14 , wherein a change of temperature in the pressure transducer results in a difference between an unstressed length of the sensor and a radial distance on the diaphragm between a location where the sensor is bonded at a center of the diaphragm and where the sensor is bonded at the rim.
26. The pressure transducer of claim 14 , wherein the accommodation structure is positioned toward one end of the sensor between the two bending areas and one of the bonded ends of the sensor.
27. The pressure transducer of claim 14 , wherein bonds at the ends of the sensor subjects ends of the sensor to full distortion of a thermal expansion difference.
28. The pressure transducer of claim 14 , wherein the sensor is positioned to minimized an effect of distortion on the one or more piezoresistors.