Microcantilever heater-thermometer with integrated temperature-compensated strain sensor
View Patent ↗The present invention provides microcantilever hotplate devices which incorporate temperature compensating strain sensors. The microcantilever hotplate devices of the present invention comprise microcantilevers having temperature compensating strain sensors and resistive heaters. The present invention also provides methods for using a microcantilever hotplate for temperature compensated surface stress measurements, chemical/biochemical sensing, measuring various properties of compounds adhered to the microcantilever hotplate surface, or for temperature compensated deflection measurements.
1. A microhotplate comprising:
a. a cantilever having a fixed end and a free end;
b. a pair of piezoresistive sensors integrated into said cantilever near said fixed end, wherein a first piezorestive sensor is aligned along a first crystal axis of said cantilever and has a first piezoresistive coefficient, and wherein a second piezoresistive sensor is aligned along a second crystal axis of said cantilever and has a second piezoresistive coefficient that is less than said first piezoresistive coefficient; and
c. a heater-thermometer integrated into said cantilever.
2. The microhotplate of claim 1 wherein said second piezoresistive coefficient has a value selected from the range of 0 to 1 Ω per μm of cantilever deflection.
3. The microhotplate of claim 1 wherein said first piezoresistive coefficient has a value selected from the range of 0.1 to 100 Ω per μm of cantilever deflection.
4. The microhotplate of claim 1 wherein the distance between said fixed end of said cantilever and said piezoresistive sensors is less than 50% of the total length of said cantilever.
5. The microhotplate of claim 1 wherein said first and second piezoresistive sensors are positioned in said cantilever in proximity to each other such that they have a substantially identical temperature.
6. The microhotplate of claim 1 wherein said cantilever comprises single crystal silicon.
7. The microhotplate of claim 6 wherein said first crystal axis is a <110> direction in silicon and said second crystal axis is a <100> direction in silicon.
8. The microhotplate of claim 1 wherein said first and second piezoresistive sensors comprise doped silicon.
9. The microhotplate of claim 8 wherein said piezoresistive sensors are doped with an element selected from the group consisting of phosphorous, boron, and other elements that are soluble in the material of the cantilever and that change the cantilever material properties.
10. The microhotplate of claim 8 wherein said piezoresistive sensors have a dopant concentration selected from the range of 10 14 to 10 20 dopants per cubic centimeter.
11. The microhotplate of claim 1 wherein said first and second piezoresistive sensors have substantially identical dimensions and substantially identical compositions.
12. The microhotplate of claim 1 further comprising a resistance sensing circuit electrically connected to said first and second piezoresistive sensors.
13. The microhotplate of claim 12 wherein said resistance sensing circuit comprises a Wheatstone bridge circuit.
14. The microhotplate of claim 12 wherein said Wheatstone bridge circuit compensates for a change in the resistance of said first and second piezoresistive sensors due to temperature.
15. The microhotplate of claim 1 wherein said heater-thermometer comprises a resistive heater.
16. The microhotplate of claim 1 wherein said heater-thermometer comprises doped silicon.
17. The microhotplate of claim 16 wherein said heater-thermometer is doped with an element selected from the group consisting of phosphorous, boron, and other elements that are soluble in the material of the cantilever and that change the cantilever material properties.
18. The microhotplate of claim 16 wherein said heater-thermometer has a dopant concentration selected from the range of 10 14 to 10 20 dopants per cubic centimeter.
19. The microhotplate of claim 1 wherein said heater-thermometer is positioned at said free end of said cantilever.
20. The microhotplate of claim 1 wherein said heater-thermometer comprises substantially an entire surface area of said cantilever.
21. The microhotplate of claim 1 wherein said heater-thermometer is capable of producing temperatures up to 1300° C. in said cantilever.
22. The microhotplate of claim 1 wherein said first and second piezoresistive sensors are in thermal communication with said heater-thermometer.