Thermoelectric Microsensor Based on Ultrathin Si Films

Gustavo Gonçalves Dalkiranis,Javier Rodriguez-Viejo,Aitor Lopeandía-Fernández,Llibertat Abad-Muñoz,Pablo Ferrando-Villalba

doi:10.3390/proceedings2131517

Abstract

We show the use as a thermal photosensor of a thermoelectric (TE) microsensor based on ultrathin suspended Si films. The reduced thickness of the structural films enhances the extremely large thermal insulation of the sensing area (~43 µW/K), since phonons scatter in the surfaces, and guarantees a reduced thermal mass (in the µJ/K range). The sensitivity of the device is evaluated by heating with an argon laser (λ = 457 nm) in the range 0–10 mW, reaching sensitivities of around 6 × 108 V/(W·m2) in high vacuum conditions and 5 × 107 V/(W·m2) in environments of air at atmospheric pressure. Open circuit voltage measurements with and without light illumination with a 406 nm diode laser operating at 4 mW were conducted at temperature differences up to 50 K between the central hot region and the Si frame. The slight decrease of the Seebeck coefficient is related to the increase of carriers by photogeneration.

Highlights

Photosensors are sensors able to detect light
We present a microsensor made from a SOI wafer where a central silicon free-standing membrane (0.25 mm2 area) hangs from a bulk silicon frame through 40 thermoelectric silicon legs (20 doped with B and 20 doped with P) [1]
The linear increase of the Seebeck voltage is due to the temperature difference induced by the laser beam between the central region and the silicon frame

Summary

Introduction

Photosensors are sensors able to detect light (electromagnetic waves). Depending on the desired spectral sensitivity different physical principles should be considered. Between sensors using semiconductors as active materials we can highlight those directly working from:. (i) photoelectric or photovoltaic effects, when the photons have energies over the semiconductor band gap. (ii) thermal-based absorption sensors when the photon energies require the generation of mid- gap states providing energy to the phonon bath. Among the wide family of thermal absorption photosensors those based on the TE principle do not require an external current or voltage source, and may offer extremely low energy detection limits depending on designs. The simplicity of that type of devices enables their miniaturization, a key factor to improving the sensitivity since it permits to reduce the heat capacity and addenda the thermal isolation of the sensing/absorbing regions. We present a microsensor made from a SOI wafer where a central silicon free-standing membrane (0.25 mm area) hangs from a bulk silicon frame through 40 thermoelectric silicon legs (20 doped with B and 20 doped with P) [1]

Methods

Results

Conclusion