Authors: R.P. Manginell, D.A. Rosato, D.A. Benson and G.C. Frye-Mason
Affilation: Sandia National Laboratory, United States
Pages: 663 - 666
Keywords: microhotplate, preconcentrator, IR microscope, chemical analysis, TAS
A hand-held chemical laboratory (mChemLab) is being developed that utilizes a silicon- nitride-supported microhotplate in the front-end, gas sampling and preconcentration stage. Device constraints include low-power (<200mW at 5V), rapid heating (<20msec), and a relatively uniform temperature distribution throughout the heated area (~3mm2). To optimize for these criteria, the electro-thermal behavior of the microhotplate was modeled using Thermal Analysis System (TAS). Predicted steady-state and transient behavior agree well with infrared (IR) microscope data and measured transient response for a low-stress silicon nitride thermal conductivity of kn = 6.4?10-2 W?(cm??C)-1 and a convection coefficient of hcv = 3.5?10-3 W?(cm2??C)-1. The magnitude of hcv is framed in the context of vacuum measurements and empirical data. Details and limitations of the IR measurement are discussed. Finally, the efficacy of methods for reducing thermal gradients in the microhotplateís active area is presented.