Micromechanical Calorimeter with Picojoule-Sensitivity

Abstract

The performance of a micromechanical calorimeter is described. Small heat pulses or heat fluxes are detected with a micromachined cantilever. The heat is transported on the cantilever towards the heat sink, causing an inhomogeneous temperature distribution which is determined by the geometry and heat conductivity of the cantilever. Those tiny temperature variations (=10-5 K) cause deflections according to the principles of bimetallic strips. Different deflection sensors, being all based on force microscopy techniques, are implemented and allow the measurement of distances as small as 0.01A. Calibration procedures, such as heating with laser light and internal ohmic resistors, are applied and compared to a model based on classical mechanics and thermodynamics. By optimizing the geometrical dimensions and material properties, such as heat conductivity and thermal expansion coefficients, the ultimate limits of such a device are estimated on the basis of the model.