Thermal sensitivity in piezoresistive sensors used in silicon microcantilevers makes them susceptible to unwanted signals such as temperature drift. In addition, when used in chemical sensing, current microcantilevers have difficulty testing femtogram (10-15) scale samples due to the effect of temperature variations on the mechanical signal. This invention is a microcantilever hotplate with both a resistive heater and temperature-compensated piezoresistive strain gauges that correct for the effect of temperature variations on the mechanical strain signal. This enables the ability to test samples in femtogram quantities allowing the preservation of highly valuable materials such as DNA samples or new drug compounds. In contrast, samples tested on the milligram scale prove to be costly since the samples are often discarded after testing.
Microcantilevers with integrated piezoresistive strain sensors are mainly used to replace optical (laser) deflection sensing thus reducing design complexity and cost. They may also be employed in various sensing applications such as gas flow sensing, acceleration sensing, microjet measurements and bio/chemical sensing. As bio/chemical sensors, piezoresistive microcantilevers are often prepared with a selective coating that is sensitive to a specific analyte. Analyte adsorption induces static deflection of the microcantilever by creating a surface stress, thus enabling embedded piezoresistors to measure analyte adsorption on the cantilever.
Microcantilevers with both resistive heaters and piezoresistors can also offer simultaneous heating and sensing. Two different cantilever designs with the same surface area have been designed with integrated heaters along the cantilever edges and a pair of piezoresistors for temperature-compensated strain gauges. The fabricated devices show successful integration of resistive heaters and piezoresistors. These microcantilever hotplates could enable simultaneous calorimetric and thermogravimeteric measurements by operating the heater and the piezoresistor pair together.
Applications
Thermomechanical data storage, biomorph actuation; nanoscale thermal analysis and manufacturing; material diagnostic characterization; calorimetry; and biochemical sensing.
Benefits
- Improves response time and enhances temperature uniformity
- Combines resistive heaters and piezoresistors on a microcantilever, which can be used as multi-functional scanning probes
- Enables materials testing at the femtogram scale
- A pair of piezoresistors in close proximity and aligned at 45, means excellent temperature compensation: 10 percent shift in deflection sensitivity for heating up to 200 C
- Has a time constant less than 1 millisecond, with maximum operation temperatures greater than 1000C