Micro-Differential Scanning Calorimeter for Combustible Gas Sensing

Published

January 1, 2004

Author(s)

Richard E. Cavicchi, G Poirier, N H. Tea, Muhammad Y. Afridi, David W. Berning, Allen R. Hefner Jr., John S. Suehle, Michael Gaitan, Stephen Semancik, Christopher B. Montgomery

Abstract

A micron-scale differential scanning calorimeter (mDSC) has been produced on a silicon chip allowing for microscopic differential scanning calorimetry measurements on small samples. The device consists of a suspended rectangular microhotplate with sample and reference zones at either end, each with a polysilicon microheater for temperature control. The temperature difference between the two zones is measured with a thermopile consisting of a series of successive polysilicon/metal junctions which alternate between the two zones. In a scanning differential calorimetry measurement, the two elements are heated simultaneously with a ramped temperature profile. A thermal process zone is defined on one of the elements, for example, a catalyst for chemical sensing, a material which exhibits a phase transition, or a chemically selective reactive material. When temperature is scanned the loss or gain of heat associated with the reaction or phase transition on the sample zone produces a difference signal on the thermopile. The device has a temperature range from 20 C to 600 C, and can be heated to that temperature in as little as 40 ms, while the cooling time constant is 5 ms. Thermal imaging was used to characterize heat flow across the device in response to a 40 ms voltage pulse applied to one side. At 4 ms after the pulse the heat distribution has become largely uniform across the device, showing that scans shorter than this time scale will minimize the effects of heat loss from the sample to the reference zone. An example application shows the response to varying concentrations of methanol, ethanol, acetone, benzene, and hydrogen in air, when operated with periodic ramps to 570 C of duration 3.5 s. The thermopile responds with a periodic waveform which is different for different gases, making the use of pattern recognition analytical methods for gas identification possible.

Citation

Sensors and Actuators B-Chemical

Volume

97

Pub Type

Journals

Download Paper

https://doi.org/10.1016/S0925-4005(03)00515-X

Keywords

calorimetry, catalyst, gas sensor, microhotplate

Citation

Cavicchi, R. , Poirier, G. , Tea, N. , Afridi, M. , Berning, D. , Hefner, A. , Suehle, J. , Gaitan, M. , Semancik, S. and Montgomery, C. (2004), Micro-Differential Scanning Calorimeter for Combustible Gas Sensing, Sensors and Actuators B-Chemical, [online], https://doi.org/10.1016/S0925-4005(03)00515-X (Accessed October 6, 2024)