Fabrication Of Flat RF MEMS Switch Membrane By Minimizing Of Stress Gradients In The Au Membrane Structure
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Fabrication Of Flat RF MEMS Switch Membrane By Minimizing Of Stress Gradients In The Au Membrane Structure Jong-Seok Kim, Hoon Song, Jin Woo Cho1, Eun Sung Lee, Sun Hee Park, Mun Chul Lee, Dong Hwa Shim, In Sang Song, Jung Woo Kim2, Seok Jin Kang and Ki Moo Song ME Center, MEMS Laboratory, Samsung Advanced Institute Of Technology, 416, Mae-tan 3 dong, Pal-dal-gu, Su-won city, Korea 442-742 E-mail : [email protected] 1 CSE Center, 2MD Laboratory ABSTRACT RF MEMS(Micro-Electro-Mechanical-System) switch technology is one of powerful solution for future RF systems. This technology provides low insertion loss, High linearity and broad bandwidth. Wide driving membrane used MEMS switch can reduce driving voltage but it is easy to bend because of the stress gradient. In order to solve this problem we fabricated Au cantilever in various sputtering condition and various substrate materials. As a result of this experiment, we fabricated cantilever which was bent within 1 um, with 2 um thickness and 340 um length. We applied this condition to RF MEMS switch and we fabricated switch membrane within 1 um bend, under 10MPa stress gradient.
INTRODUCTION The most remarkable tendency in the recent cellular phone technology is a multi-functional integration with smaller size and lighter weight. In this purpose, not a just miniaturization but device integration by the new method is essentially needed. One of methods is a fabrication of RF device by MEMS technology. MEMS device may be fabricated various ways using processes have been extended to achieve three dimensional structures by the techniques of bulk micro-machining, in which large amounts of the substrates are removed, or surface micromachining in which layers are deposited on the surface followed by the removal of a sacrificial layer to release a moving structure.[1] RF MEMS switch fabricated by MEMS technology has many advantages such as low insertion loss, high isolation, low current consumption, excellent IP3 characteristic and high power capability. However, it requires a higher driving voltage than conventional switches. Recently, many researchers have extensively studied RF switches operated in low voltage. In the development of low voltage driving RF switch, one of the big problems is that driving voltage is increased by the bend of Au membrane. This kind of bend is caused by internal stress degree of slop. The range of the bend is several micro-meter. Figure 1( a ) is a photograph of RF MEMS switch and figure 1( b ) image is a picture taken by optical 3D profiler. By using this equipment, we could measure X and Y direction profiles of switch membrane which bended 2.4um in X direction, 2.1um in Y direction. In order to find out control methods and critical factors that affect stress gradient, we fabricated Au cantilever with different width, different length and by changing sputter deposition pressure, temperature, RF powers, sacrificial layer materials and substrate materials.
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Spring Switch membrane
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CPW signal line Spring Y profile
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