**9. Conclusion**

Bulk and surface micromachining are the two most widely used techniques for fabrication of MEMS devices. Wet and dry etching is used to achived the final release of the MEMS devices. However, in surface micromachining a combination of wet and dry etching techniques is used. Pros and cons of both the techniques have been disscused in the chapter. In wet etching capilary forces developed during the process leads to stiction and permanent adhesion of the MEMS devices. To eliminate the chance of stiction and permanent adhesion between the two solid surfaces, an inter-solid surface adhesion reduction is required. The textured surfaces and posts approach has been used for to eliminate the inter-solid surface adhesion. This was done firstly, by introducing a dimple as a supporting post between two solid surfaces and secondly, by reducing the contact area between the two metal surfaces. Both the methods were used to design improved switches which include the stiction mitigation structures. In dry etching, a dry release method with better solution for release of RF MEMS structures has been used. The technique was developed using RIE instead of CO2 dryer or critical point drying technique. This process may lead to long term storage of the MEMS devices. Finally, fabricated novel switches have been presented validating the developed fabrication process.

A six mask all metal fabrication process was used for fabrication of RF MEMS switches. The experimental RF performance of the two fabricated swithes achieved a measured actuation voltages of 19V and 23V, respectively. Both switches showed good RF performance. Design-1 exhibited an isolation of 28dB at 20GHz and better than 23dB at 40GHz whereas, Design-2 exhibited an isolation of 30dB at 20GHz and better than 28dB at 40GHz. Both RF MEMS designs showed good impedance matching to 50Ω as deducted from the ON state Sparameter measurements. A return loss better than 22dB at 20GHz and 19dB at 40GHz was measured for Design-1 whereas, Design-2 exhibited a return loss of better than 20dB at 20GHz and 18dB at 40GHz. The insertion loss was 1.15dB and 1.3dB respectively, for all frequency band of interest.

### **10. Acknowledgment**

This research was carried out at Centre for Quantum Computer Technology (CQCT) Micro Fabrication Laboratory, University of New South Wales (UNSW), Australia. The author wishes to thank Professor Rodica Ramer for continuous support and supervision during the whole research The helpful advice by Dr Eric Gauja during the fabrication is greatly appreciated.

#### **11. References**

288 Microelectromechanical Systems and Devices

but at this point full boundary conditions were not enforced. When boundary condition were fully enforced and beam was placed in the hold down position the complete surface of dimple was not in contact and front surface of dimple has lifted up as shown in figure 21(e).

The measured actuation voltage of the Design-1 is 19V and Design-2 is 23V. A number of release holes can be observed in the fabricated switches. The effect on electrostatic force due to release holes had already been rationalized with inclusion of 40% of fringing field effect

Bulk and surface micromachining are the two most widely used techniques for fabrication of MEMS devices. Wet and dry etching is used to achived the final release of the MEMS devices. However, in surface micromachining a combination of wet and dry etching techniques is used. Pros and cons of both the techniques have been disscused in the chapter. In wet etching capilary forces developed during the process leads to stiction and permanent adhesion of the MEMS devices. To eliminate the chance of stiction and permanent adhesion between the two solid surfaces, an inter-solid surface adhesion reduction is required. The textured surfaces and posts approach has been used for to eliminate the inter-solid surface adhesion. This was done firstly, by introducing a dimple as a supporting post between two solid surfaces and secondly, by reducing the contact area between the two metal surfaces. Both the methods were used to design improved switches which include the stiction mitigation structures. In dry etching, a dry release method with better solution for release of RF MEMS structures has been used. The technique was developed using RIE instead of CO2 dryer or critical point drying technique. This process may lead to long term storage of the MEMS devices. Finally, fabricated novel switches have been presented validating the

A six mask all metal fabrication process was used for fabrication of RF MEMS switches. The experimental RF performance of the two fabricated swithes achieved a measured actuation voltages of 19V and 23V, respectively. Both switches showed good RF performance. Design-1 exhibited an isolation of 28dB at 20GHz and better than 23dB at 40GHz whereas, Design-2 exhibited an isolation of 30dB at 20GHz and better than 28dB at 40GHz. Both RF MEMS designs showed good impedance matching to 50Ω as deducted from the ON state Sparameter measurements. A return loss better than 22dB at 20GHz and 19dB at 40GHz was measured for Design-1 whereas, Design-2 exhibited a return loss of better than 20dB at 20GHz and 18dB at 40GHz. The insertion loss was 1.15dB and 1.3dB respectively, for all

This research was carried out at Centre for Quantum Computer Technology (CQCT) Micro Fabrication Laboratory, University of New South Wales (UNSW), Australia. The author wishes to thank Professor Rodica Ramer for continuous support and supervision during the

during simulation of spring constant of the beam designs (Rebeiz, 2003).

This phenominon lead to higher insertion loss.

**8.1.3 Actuation voltage** 

developed fabrication process.

frequency band of interest.

**10. Acknowledgment** 

**9. Conclusion** 


**12** 

*1,2Thailand 3USA* 

**Optical MEMS** 

Wibool Piyawattanametha1,2 and Zhen Qiu3

*Chulalongkorn University, Pathumwan,* 

*1Advanced Imaging Research (AIR) Center, Faculty of Medicine,* 

*2National Electronics and Computer Technology Center, Pathumthani, 3University of Michigan, Biomedical Engineering, Ann Arbor, Michigan* 

In 1989, a group of scientists and engineers in Salt Lake City started a workshop called Micro-Tele-Operated Robotics Workshop. There, the acronym for Microelectromechanical systems (MEMS) was officially adopted. However, MEMS technology has already had a head start since at least 7 years ago from the classic work published by Petersen in 1982 [1]. Twenty years later, MEMS technology has started major novel innovations in several scientific fields and created highly promising market potential. In 2003, the most

Optics and photonics are among these research fields impacted by MEMS techniques. Optical MEMS has created a new fabrication paradigm for optical devices and systems. These micro optical devices and systems are inherently suited for cost effective wafer scale manufacturing as the processes are derived from the semiconductor industry. The ability to steer or direct light is one of the key requirements in optical MEMS. In the past two decades since Petersen published his silicon scanner [1], the field of optical MEMS has experienced explosive growth [2,3]. In the 80's and early 90's, displays were the main driving force for the development of micromirror arrays. Portable digital displays are commonplaces and head mount displays are now commercially available. In the past decade, telecommunications have become the market driver for Optical MEMS. The demand for routing internet traffic through fiber optic networks pushes the development of both digital and scanning micromirror systems for large port-count all-optical switches with the ability to directly manipulate an optical signal, Optical MEMS systems eliminate unnecessary optical-electrical-optical (O-E-O) conversions. In the biomedical arena, micro-optical scanners promise low-cost endoscopic three-dimensional imaging systems for *in vivo*

This chapter summarizes the state of the art of Optical MEMS technology by describing basic fabrication processes to derive with actuation mechanisms and select examples of devices that are either commercially available, or show great promise of becoming products in the near term. The chapter is organized into the following sections: Section 2 describes the generic actuation mechanisms commonly used for MEMS devices. Section 3 discusses the

conservative market studies predict a world MEMS market in excess of \$8 billion.

**1. Introduction** 

diagnostics.

applications.

