Maintaining Transparency of a Heated MEMS Membrane for Enabling Long-Term Optical Measurements on Soot-Containing Exhaust Gas

Abstract

Ensuring optical transparency over a wide spectral range of a window with a view into the tailpipe of the combustion engine, while it is exposed to the harsh environment of soot-containing exhaust gas, is an essential pre-requisite for introducing optical techniques for long-term monitoring of automotive emissions. Therefore, a regenerable window composed of an optically transparent polysilicon-carbide membrane with a diameter ranging from 100 µm up to 2000 µm has been fabricated in microelectromechanical systems (MEMS) technology. In the first operating mode, window transparency is periodically restored by pulsed heating of the membrane using an integrated resistor for heating to temperatures that result in oxidation of deposited soot (600–700 °C). In the second mode, the membrane is kept transparent by repelling soot particles using thermophoresis. The same integrated resistor is used to yield a temperature gradient by continuous moderate-temperature heating. Realized devices have been subjected to laboratory soot exposure experiments. Membrane temperatures exceeding 500 °C have been achieved without damage to the membrane. Moreover, heating of membranes to ΔT = 40 °C above gas temperature provides sufficient thermophoretic repulsion to prevent particle deposition and maintain transparency at high soot exposure, while non-heated identical membranes on the same die and at the same exposure are heavily contaminated.

Integrated Digital and Analog Circuit Blocks in a Scalable Silicon Carbide CMOS Technology

“…Together with galium nitride (GaN), the future market of wide-bandgap materials in power electronics is expected to be booming [3]. This foresight and the developed technologies pave the way for application in other fields as well [4]- [7], such as harsh environment sensing [8], [9] and ultraviolet detectors, though there are challenges for the next generation of devices to overcome [10].…”

Resistive and CTAT Temperature Sensors in a Silicon Carbide CMOS Technology

“…Due to the large demand of SiC and GaN based power devices, material costs are steadily decreasing. This development is expected to enable other cost-effective future application of these materials, like integrated systems in harsh environment sensing [4][5][6][7][8][9].…”