**Author details**

placement on the platinum coated carrier wafer. The second step of the process was to perform backside silicon DRIE to achieve proof mass thickness of approximately 40 µm. The same plasma silicon etcher was used to anisotropically etch the silicon substrate to the desired thickness. Fig. 22 shows the FESEM image of the successfully released MEMS chemical sensor with the inset showing a close-up

Fig. 21: 2-D Schematic of the resonant MEMS chemical sensor

The post-CMOS micromachining process steps of the resonant MEMS chemical sensor were similar to the process steps of the resonant MEMS magnetic field sensor. The process started with the selective application of photoresist at the back-side of the die around the sensor followed by sample

SCS underneath the interconnect layers

Fig. 20: FESEM image of the fabricated CMOS-MEMS resonant magnetic field sensor with inset showing shuttle and stator fingers.

In resonant MEMS chemical sensors, known as gravimetric sensors, the principle of detection of the gaseous species is based on the change in resonant frequency of the microresonator membrane or plate. This frequency change results from a change in the mass of the microresonator due to absorption/adsorption of an analyte molecule onto the surface of the active material deposited on it.

Fig. 22: FESEM image of fabricated device with inset showing a close-up view of the fingers with the SCS underneath

**Figure 22.** FESEM image of fabricated device with inset showing a close-up view of the fingers with the SCS underneath

This chapter discussed bulk micromachining technology with particular emphases on DRIE post CMOS MEMS bulk micromachining. The chapter was divided into three sections. In the first section an introduction to bulk micromachining of silicon and isotropic and anisotropic wet and dry etching was given. The second section discussed briefly DRIE post-CMOS micromachining process with particular emphasis on DRIE post-CMOS bulk micromachining process and the third and last section provides a few examples of devices fabricated by our research group using the DRIE CMOS-MEMS process. These devices were resonant MEMS magnetic field sensor and resonant MEMS chemical sensor. The aim of the chapter was to discuss and analyze practical processes involved in the design

This chapter discussed bulk micromachining technology with particular emphases on DRIE post CMOS MEMS bulk micromachining. The chapter was divided into three sections. In the first section an introduction to bulk micromachining of silicon and isotropic and anisotropic wet and dry etching was given. The second section discussed briefly DRIE post-CMOS micromachining process with particular emphasis on DRIE post-CMOS bulk micromachining process and the third and last section provides a few examples of devices fabricated by our

The authors would like to thank MIMOS Bhd Malaysia for facilitating the microfabrication of the sensors and MOSTI Malaysia for financially supporting this research under E-Science project

[1]. Hongwei Qu and Huikai Xie, "Process Development for CMOS-MEMS Sensors with Robust Isolated Bulk Silicon Microstructures", *IEEE/ASME Journal of Micro-Electro-Mechanical* 

of micromechanical devices using 0.35 µm CMOS technology.

view of the perfectly flat sensing comb fingers with the SCS underneath [15].

**Figure 21.** D Schematic of the resonant MEMS chemical sensor

Fig. 21 shows 2-D schematic diagram of the chemical microsensor device.

136 Advances in Micro/Nano Electromechanical Systems and Fabrication Technologies

**3.2 Resonant MEMS Chemical sensor**

Dummy Structures

**Conclusion**

**4. Conclusion**

**Acknowledgment**

No.04-02-02-SF0095.

*System*s, Vol. 16, 5, pp. 1152-1161.

**References**

John Ojur Dennis, Farooq Ahmad and M. Haris Khir

Department of Fundamental and Applied Sciences, Department of Electrical and Electronic Engineering, Universiti Teknologi PETRONAS, Perak, Malaysia
