| AVS 54th International Symposium | |
| Manufacturing Science and Technology | Thursday Sessions |
| Session MS-ThA |
| Session: | MEMS Manufacturing |
| Presenter: | C. Zhan, Sharp Laboratories of America, INC. |
| Authors: | C. Zhan, Sharp Laboratories of America, INC. P. Schuele, Sharp Laboratories of America, INC. J. Conley, Sharp Laboratories of America, INC. J. Hartzell, Sharp Laboratories of America, INC. |
| Correspondent: | Click to Email |
This paper reports a novel integrated biosensor based on the piezoresistive effect of laser crystallized silicon (c-Si) thin film. The sensor is comprised of a c-Si resistor integrated on a PECVD SiO2 cantilever using low temperature surface micromachining techniques. Once the cantilever is deflected mechanically, the electrical response of the integrated thin film resistor changes accordingly. The fabrication and measurement results of crystallized silicon thin film resistor on a cantilever are presented. Our unique laser crystallized a-Si film enables a high quality thin film piezoresistor be accommodated on a small and thin cantilever using MEMS surface micromachining techniques. The integrated piezoresistive cantilever transducer can be selectively functionalized and implemented in large arrays for biosensing applications. The device consists of a c-Si thin film resistor embedded in a PECVD SiO2 cantilever. The air gap between the cantilever and the substrate is defined by a PECVD a-Si sacrificial film, which was removed during release etch step. When the cantilever is deflected by an external force, pressure or surface stress, a uniaxial strain is induced along the longitudinal direction of the cantilever. The strain stretches or compresses the thin film resistor and therefore changes the resistance. The fabrication process is a standard TFT process flow compatible surface micromachining process. Only two extra masks, one for sacrificial mesa patterning and another for cantilever outline patterning, are introduced to the standard TFT flow to realize the c-Si TFT based piezoresistive cantilever biosensor. A 1.5 um thick a-Si is PECVD deposited as the sacrificial film and a TMAH based release etchant is used to release the MEMS cantilever. The PECVD SiO2 films of the standard TFT process are used to form the body of the cantilever. One design of the cantilever is 140um long, 50um wide and 0.5um thick. The c-Si TFT active thin film is used to form the piezoresistor. The thickness of the active c-Si piezoresistor is 100nm. Initial tests on our fabricated MEMS piezoresistive biosensors confirm the piezoresistive effect. External mechanical actuation tests were performed using a micropositioner for calibration. The minimum detectable cantilever deflection is 3nm at 3dB signal to noise ratio. Currently, the sensitivity of the fabricated cantilever biosensor is 3.07uv/nm. The biosensing tests are on the way and results will be updated.