Micromachined poly-SiGe bolometer arrays for infrared imaging and spectroscopy

Abstract

The state-of-the-art characteristics of micromachined polycrystalline SiGe microbolometer arrays are reported. An average NETD of 85 mK at a time constant of 14 ms is already achievable on typical self-supported 50 µm pixels in a linear 64-element array. In order to reach these values, the design optimization was performed based on the performance characteristics of linear 32-, 64-and 128-element arrays of 50-, 60-and 75-µm-pixel bolometers on several detector lots. The infrared and thermal modeling accounting for the read-out properties and self-heating effect in bolometers resulted in improved designs and competitive NETD values of 80 mK on 50 µm pixels in a 160×128 format at standard frame rates and f-number of 1. In parallel, the TCR-to-1/f noise ratio and the mechanical design of the pixels were improved making poly-SiGe a good candidate for a low-cost uncooled thermal array. The technological CMOSbased process possesses an attractive balance between characteristics and price, and allows the micromachining of thin structures, less than 0.2 µm. The resistance and TCR non-uniformity with σ/µ better than 0.2% combined with 99.93% yield are demonstrated. The first lots of fully processed linear arrays have already come from the IMEC process line and the results of characterization are presented. Next year, the first linear and small 2D arrays will be introduced on the market.

A study on microbolometer electro-thermal circuit modelling

“…Although there are many materials commonly used in microbolometer fabrication -Titanium (Ti) [9], Vanadium Oxide (VO) [10], Yttrium barium copper oxide (YBaCuO, YBCO) [11], GeSiO [12], poly SiGe [13], BiLaSrMnO and others -the most attractive among them are semiconductor (amorphous silicon Į-Si, poly-Si, Si-Ge) [4], because they have a higher temperature coefficient of resistance (TCR) than other materials.…”

An all-ZnO microbolometer for infrared imaging

“…In terms of thermistor materials, most of the commercially available microbolometers employ vanadium oxide (VO x ) and amorphous silicon (a-Si) with TCR values between À2%/K and À3%/K [3,4]. In addition, alternative active materials reported include but are not limited to thin film metals such as titanium (0.35%/K) [8] and platinum (0.14%/K) [9], YBaCuO (À3.3%/K) [10] and poly crystalline silicon germanium, poly-SiGe ($1%/C) [11]. Besides these, there are also reports on the usage of electronic devices such as Si based diodes (À2 mV/K) [12], thin film transistors (6.5%/K) [13] and SiGe quantum wells (À5.8%/K) [14].…”

Investigations on titanium oxide film as an alternative heat sensitive material

“…Therefore, heat sensitive material is one of the most essential parts of microbolometer fabrication. There are several alternative materials for the heat sensitive material such as silicon dioxide [3], Ti [4], poly SiGe [5], Vanadium oxide [6], amorphous silicon [7], silicon carbide [8] and so on. Among these, vanadium oxide (VO X ) and amorphous silicon (а-Si) are widely accepted materials for commercialized focal plane arrays due to their high temperature coefficient of resistance and relatively low noise property [9].…”