Differential Scanning Calorimeter Based on Suspended Membrane Single Crystal Silicon Microhotplate

Abstract

This paper introduces an array of single crystal silicon microhotplates for differential scanning calorimetry. Heat transfer analysis considers the tradeoffs between heating and cooling rate, temperature uniformity, and measurement sensitivity, and determines the optimal design for a suspended membrane microhotplate with full backside release. Additionally, considering the requirements of routine sample loading, the size of the square heater (L-H) is 100 or 200 mu m, while the size of the backside membrane cavity is 400 mu m. In the heater region, two interdigitated serpentine doped silicon resistors were designed such that several operational configurations were possible. The hotplates exhibited very high heating efficiency of 36.7 K/mW with L-H = 100 mu m and 18.3 K/mW with L-H = 200 mu m while also having time constants on the order of 1 ms. Paraffin wax was mounted on the sensor, and melting was observed when the heater temperature was 55 degrees C with a voltage ramp of 0.2 V/s. With 8 V/s, the paraffin sample was completely consumed within 1 ms with 0.317 mJ of thermal energy extracted. Our design achieves a combination of time constant, temperature sensitivity, and heating efficiency that are comparable or superior to previously published microcalorimeters.