Torwards a fully-integrated CMOS microcalorimeter with on-chip quasi-digital output signal

We analyze and characterize the static and dynamic thermal response of two sub-micrometer scale metal beam resonators to evaluate its potential as resonant thermal sensors. The fabricated resonators are a cantilever and a CC-beam which resonant frequency, around 6.5 MHz and 15 MHz respectively, changes due to the heat received from a probe pad, acting as a sample stage, through a metal track. Unlike other works, where off-chip piezoelectric excitation and optical readout are used, the mechanical resonator constitutes the frequency-determining element of an oscillator circuit that is fully-integrated in a 0.35-μm CMOS chip. For this first prototypes a heat conduction efficiency of 5.5% has been obtained for the metal CC-beam and a temperature resolution at the sample stage as low as 3.5 mK. In addition, some sensor layout considerations are detailed to further increase the sensor performance in future designs.