Length-extensional resonating gas sensors with IC-foundry compatible low-cost fabrication in non-SOI single-wafer

This study presents 'dog-bone' structured bulk-mode resonant gas sensors that can be low-cost volume fabricated in standard IC foundries. Without the need for MEMS-specific processes like double-side aligned photolithography and wafer-to-wafer bonding, the sensor fabrication can be completed in standard IC-foundries, thereby showing advantage in low-cost mass production and application. Based on a diaphragm-on-cavity structure made by a MIS (micro-openings inter-etch and sealing) micromachining technology in ordinary (non-SOI) single-wafer, the resonator fabrication is further completed with simple dry etching and metal interconnection. With similar fabrication scheme to semiconductor IC chips, herein the 3-D micromachining processes are only implemented from the front-side of the wafer (with unpolished wafer backside) and all the fabrication steps utilize IC-foundry available processes. After loading with gas sensitive material, the resonant sensors are ready for application. For comparison, traditional sensors with identical resonator structure are also fabricated in SOI wafer with double-sided process. Besides the measured similar resonance performance for the two sensors, the new sensor is advantageous in smaller dimensions (0.5 mm x 0.5 mm) and much lower volume-fabrication cost (in ASMC, a 6-inch IC foundry company in Shanghai) of one US-cent per sensor. By loading an organo-phosphor sensitive chemical-group modified hyper-branched polymer onto the new resonator, the disposable biochemical micro-sensor is used to rapidly detect organophosphorous pesticide residue for food-safety and agriculture applications. The resonant chemical sensor experimentally performs linear and repeatable detection of ppm-level organo-phosphorous vapor. (C) 2015 Elsevier B.V. All rights reserved.