Low pressure sensor device with high accuracy and high sensitivity
View Patent ↗Pressure non-linearity in a low pressure sensor device formed from a silicon diaphragm with an embedded piezoresistive transducer is reduced by using a shallow boss or thin stiffener on an ultra-thin diaphragm while the pressure sensitivity of the device is increased with corner trenches.
1. A pressure sensor comprised of:
a silicon diaphragm (diaphragm) having a first thickness between about 1 and about 10 microns and having a piezoresistive element formed therein; and
a diaphragm stiffener having a second thickness between about 1 and 20 microns, the diaphragm stiffener being attached to the diaphragm and located proximate to a center of the diaphragm.
2. The pressure sensor of claim 1 , wherein the diaphragm stiffener has a second thickness between about 1 micron and about 10 microns.
3. The pressure sensor of claim 1 , wherein the diaphragm stiffener is surface-micromachined.
4. The pressure sensor of claim 1 , wherein the stiffener has an outer perimeter and wherein the diaphragm is etched out and thinner in a plurality of regions that are distributed around the perimeter of the diaphragm.
5. The pressure sensor of claim 2 , wherein the diaphragm stiffener is rectangular.
6. The pressure sensor of claim 2 , wherein the diaphragm stiffener is square.
7. The pressure sensor of claim 2 , wherein the diaphragm stiffener is round.
8. The pressure sensor of claim 3 or 4 , wherein one etched-out region is located at each corner of the stiffener.
9. The pressure sensor of claim 8 further comprised of a sidearm between each etched-out region.
10. The pressure sensor of claim 9 , wherein the etched-out region is of a first thickness, the sidearm is of a second thickness and the stiffener is of a third thickness.
11. The pressure sensor of claim 10 , wherein the first, second and third thickness are different from each other.
12. The pressure sensor of claim 1 , wherein the stiffener is formed from the diaphragm.
13. The pressure sensor of claim 1 , wherein the stiffener is formed from a material that is different from the diaphragm.
14. The pressure sensor of claim 1 , further including a housing having a recess.
15. The pressure sensor of claim 1 , further including at least one circuit formed in the silicon diaphragm and a passivation layer formed over the diaphragm.
16. A method of forming a pressure sensor, the method comprising the steps of:
forming a shallow gap on a first side of a first die, the shallow gap having a bottom surface;
attaching a stiffener to the shallow gap bottom surface;
forming a plurality of etched out regions around the stiffener;
bonding the first die to a second die;
thinning a second side of the first die to form a diaphragm; and
forming a piezoresistive transducer on the second side of the first die.
17. The method of claim 16 , wherein the plurality of etched out regions have different thicknesses.
18. The method of claim 16 , further including the step of forming a hole through the second die.
19. The method of claim 16 , wherein the step of forming a shallow gap and the step of thinning the second side provide a diaphragm having a thickness between about 1 micron and about 200 microns.
20. The method of claim 18 , wherein the step of forming a hole through the second die includes the step of forming the hole using deep reactive ion etching (DRIE).
21. A method of forming a pressure sensor, the method comprising the steps of:
forming a shallow gap on a first side of a first die, the shallow gap having a bottom surface and where the shallow gap is formed to provide a stiffener to the shallow gap bottom surface;
forming a plurality of etched out regions around the stiffener;
bonding the first die to a second die;
thinning a second side of the first die; and
forming a piezoresistive transducer on the second side of the first die.
22. The method of claim 21 , wherein the plurality of etched out regions have different thicknesses.
23. The method of claim 21 , including the step of forming a hole through the second die.
24. The method of claim 21 wherein the step of forming a shallow gap and the step of thinning the second side provide a diaphragm having a thickness between about 1 micron and 20 microns.
25. The method of claim 21 , wherein the step of forming a hole through the second die includes the step of forming the hole using deep reactive ion etching (DRIE).
26. The method of claim 21 , wherein the step of attaching a stiffener includes the step of forming the stiffener from the first die by etching.