Characterization of the piezoresistance in highly doped p-type 3C-SiC at cryogenic temperatures.

This paper reports on the piezoresistive effect in p-type 3C-SiC thin film mechanical sensing at cryogenic conditions. Nanothin 3C-SiC films with a carrier concentration of 2 × 1019 cm-3 were epitaxially grown on a Si substrate using the LPCVD process, followed by photolithography and UV laser engraving processes to form SiC-on-Si pressure sensors. The magnitude of the piezoresistive effect was measured by monitoring the change of the SiC conductance subjected to pressurizing/depressurizing cycles at different temperatures. Experimental results showed a relatively stable piezoresistive effect in the highly doped 3C-SiC film with the gauge factor slightly increased by 20% at 150 K with respect to that at room temperature. The data was also in good agreement with theoretical analysis obtained based on the charge transfer phenomenon. This finding demonstrates the potential of 3C-SiC for MEMS sensors used in a large range of temperatures from cryogenic to high temperatures.

A microfabricated sun sensor using GaN-on-sapphire ultraviolet photodetector arrays.

A miniature sensor for detecting the orientation of incident ultraviolet light was microfabricated using gallium nitride (GaN)-on-sapphire substrates and semi-transparent interdigitated gold electrodes for sun sensing applications. The individual metal-semiconductor-metal photodetector elements were shown to have a stable and repeatable response with a high sensitivity (photocurrent-to-dark current ratio (PDCR) = 2.4 at -1 V bias) and a high responsivity (3200 A/W at -1 V bias) under ultraviolet (365 nm) illumination. The 3 × 3 GaN-on-sapphire ultraviolet photodetector array was integrated with a gold aperture to realize a miniature sun sensor (1.35 mm × 1.35 mm) capable of determining incident light angles with a ±45° field of view. Using a simple comparative figure of merit algorithm, measurement of incident light angles of 0° and 45° was quantitatively and qualitatively (visually) demonstrated by the sun sensor, supporting the use of GaN-based sun sensors for orientation, navigation, and tracking of the sun within the harsh environment of space.