With the increasing requirements for microelectromechanical systems (MEMS) regarding stability, miniaturization and integration, novel materials such as wide band gap semiconductors are attracting more attention. Polycrystalline SiC has first been implemented into Si micromachining techniques, mainly as etch stop and protective layers. However, the outstanding properties of wide band gap semiconductors offer many more possibilities for the implementation of new functionalities. Now, a variety of technologies for SiC and group III nitrides exist to fabricate fully wide band gap semiconductor based MEMS. In this paper we first review the basic technology (deposition and etching) for group III nitrides and SiC with a special focus on the fabrication of three-dimensional microstructures relevant for MEMS. The basic operation principle for MEMS with wide band gap semiconductors is described. Finally, the first applications of SiC based MEMS are demonstrated, and innovative MEMS and NEMS devices are reviewed.

http://iopscience.iop.org/article/10.1088/0022-3727/40/20/S19/pdf

Group III nitride and SiC based MEMS and NEMS: materials properties, technology and applications

Silicon carbide has attracted considerable attention in recent years as a potential material for sensor devices. This paper reviews the current status of SiC technology for a wide range of sensor applications. It is shown that SiC MEMs devices are well-established with operational devices demonstrated at high temperatures (up to 500 °C) for the sensing of motion, acceleration and gas flow. SiC sensors devices using electrical properties as the sensing mechanism have also been demonstrated principally for gas composition and radiation detection and have wide potential use in scientific, medical and combustion monitoring applications.

https://iopscience.iop.org/article/10.1088/0022-3727/40/20/S17/pdf

SiC sensors: a review

Carbon nanotubes (CNTs) show many fascinating properties and are regarded as one of the most promising nanomaterials that can be used in many kinds of application. It has been reported that CNTs can fi nd broad applications in electronics [ 1 ] and photonics. [ 2 ] Recently, their application in sensors for gases [ 3 ] and biological materials, [ 4,5 ] electrodes for fl exible electronics [ 6 ] and solar cells, [ 7 ] fi llers for polymers, [ 8 ]

Carbon-nanotube-film microheater on a polyethylene terephthalate substrate and its application in thermochromic displays.

Micromachined silicon platforms, owing to some of its inherent advantages including miniaturized dimensions, ultralow power consumption, reduced batch fabrication cost, long-term reliability, and compatibility with standard CMOS fabrication technology, attracted the attention of solid-state gas sensor researchers, particularly since the last decade. As the semiconducting gas sensing thin film on top of micromachined platforms often needs an elevated temperature to activate the sensing mechanism, the suitable electrothermal and structural design of a microheater, i.e., having fast response, uniform temperature distribution over sensing area, and minimal residual/thermal-stress-induced membrane deflection, are of prime concern. In this paper, the technological developments related to the various designs and geometries of microheaters and their fabrication technology employing different suitable heating materials, for closed- and suspended-type silicon membranes have been discussed critically with particular emphasis on the relative merits and demerits with reference to heater parameters such as power consumption, temperature distribution, response time, and mechanical stability/reliability.

Technological Journey Towards Reliable Microheater Development for MEMS Gas Sensors: A Review

The target of this work is the demonstration of advanced approaches able to provide non-silicon MEMS platforms for chemical sensor operating under harsh environmental conditions and, on the other hand, to assure microhotplate stable at high temperature, which can be used for the deposition of refractory gas-sensing materials, for example, oxides of gallium, zirconium, or hafnium. Non-silicon materials that can be used for these MEMS platforms include aluminum oxide, yttria-stabilized zirconia and thin borosilicate glass. It was shown that thin ceramic films made of oxide materials can withstand annealing temperature up to 1000 °C, MEMS sensor based on these films consumes

Non-silicon MEMS platforms for gas sensors

This paper reports on the thermal analysis of a novel micro hotplate design for metal oxide gas sensors. The hotplate is a 500 μm × 500 μm square shaped membrane made of 2 μm thick polycrystalline 3C–SiC on a silicon substrate suspended by four legs. The membrane is heated by an on chip platinum thin film heater. For reasons of a short response time and a high sensitivity a uniform temperature profile is desired. In the experiments reported here, the temperature distribution across the membrane is being measured by means of infrared thermography. To verify the absolute temperature of the thermography, reference measurements are made using an on chip platinum temperature sensor, commercially available thermal melt crayons, and K-Type micro thermocouples. The measured temperature results vary depending on the method used between 430 °C for the thermography and 870 °C with the melt crayons at a supplied heater power of 300 mW.

A. Berns

Papers

Thermal analysis of silicon carbide based micro hotplates for metal oxide gas sensors