낮은 임계 가속도를 가지는 실리콘 기반 MEMS 가속도 스위치에 관한 연구

학위논문 (박사)-- 서울대학교 대학원 공과대학 전기·컴퓨터공학부, 2017. 8. 김용권.Abstract In this paper, MEMS acceleration switch with low threshold acceleration below 10 g and fine environmental characteristics are developed. Limits of the previously reported low-g MEMS switches were addressed in terms of environmental test issues and the solutions for them were suggested and integrated in the proposed low-g MEMS acceleration switch. Fabrication process consists of one silicon-on-insulator substrate and two glass substrates for base and package, respectively. Single-crystalline silicon was chosen as the structural material for high thermal stability and stress-free structure. After the fabrication, height profiles of the free-hanging proof masses were measured to show that the fabricated switches does not suffer from stress problems. The size of single switch was measured as 2150 x 4240 x 1180 µm3 and the average proof mass, initial gap, and the spring constant was 307.38 µg, 6.39 µm, and 3.29 N/m, respectively. The calculated threshold acceleration thus was 6.98 g. In the electrostatic operation test, the response time of the switch was measured to be shorter than 1.2 ms and the minimum contact resistance was 8.5 Ω at the contact force of 284 µN. Life cycle test was carried out to show that the developed switch could operate more than 10,000 cycles without failure. Rotation-table experiment was carried out in sequence to reveal that the switch operates at 6.61 g. The error analysis was carried out in the consideration of the off-axis force generated during the rotation-table experiment. From the experimental values, the off-axis force was calculated as 2.091 μN and the resulting reduction in the initial switching gap was simulated as 0.236 μm. The reduced threshold acceleration thus was estimated to be 6.512 g, which agrees well with the measured threshold acceleration value of 6.61 g. Rotation-table test using another switch was conducted to model the relation between the off-axis force and the operating acceleration of the developed switch. Least squares method was used in the analysis and the original threshold acceleration (a_th) of the switch was calculated as 6.16325 g. The error rate (ε) due to the off-axis force was calculated as -0.22693 g/µN. The modeled operating acceleration of the switch in terms of the off-axis force matched well with the measurements, showing the maximum error less than 1.6%. Heating, sealing, high-g, and impact tests were conducted in sequence to validate the environmental characteristics of the switch. Test condition of 80 °C for 6 hours were adopted for heating test and the tested switch operated more than 200 cycles normally after the test. For sealing test, gross leak test using penetrant dye (Rhodamine B) and fine leak test using tracer gas (helium) were conducted sequentially. 10 samples were put into both of the tests. In the gross leak test, no signs of dye penetration were observed after pressurizing the samples in the dye solution. The tested switches were then put into the fine leak test. In the fine leak test, helium leak rates were measured and all of the tested samples showed leak rate lower than 5.8x10-8 atm cc/s He, which is the reject limit provided by MIL-STD-883E. High-g test and drop impact test were also performed to validate the effectiveness of the displacement-restricting structure. As a result of the high-g test, the developed switch was able to operate without breaking after experiencing the acceleration of 300 g in the ±x ̂, ±y ̂, and ±z ̂ axes. In addition, the drop impact test has proved that the developed switch can withstand an impact as high as 1000 g. The MEMS acceleration switch developed throughout this study is the first to attain low threshold and good environmental characteristics at the same time. Therefore, the author believes that the switch developed in this study is the most suitable one for safety arm unit application among the low-g switches developed so far.1. Introduction 1 1.1. Sensing of acceleration 1 1.2. Safety arm unit and MEMS acceleration switches 8 1.3. Literature review 14 1.4. Motivation and purpose 19 1.5. Contribution 20 1.6. Composition of thesis 22 2. Theory and design of low-g MEMS acceleration switch 23 2.1. Basic theories on acceleration switch 23 2.1.1 Static threshold acceleration 23 2.1.2 Determining the initial gap 25 2.1.3 Serpentine spring 27 2.1.4 Parallel plate damper 31 2.2. Model description 34 2.2.1 Base glass substrate 36 2.2.2 SOI substrate 36 2.2.3 Packaging glass substrate 37 2.3. FEM simulation 38 2.3.1 Force, displacement, stress simulation 38 2.3.2 Modal analysis Resonant frequency 40 2.4. MATLAB code for MEMS switch 45 3. Fabrication of low-g MEMS acceleration switch 63 3.1. Overall fabrication process 63 3.2. Base glass substrate 65 3.3. SOI substrate 69 3.4. Bonded susbtrate & packaging 72 3.5. Fabrication results 79 4. Characterization of low-g MEMS acceleration switch 84 4.1. DC operation test & lifecycle test 84 4.2. Rotation-table experiments 93 4.3. Effect of the off-axis force on the operating acceleration 101 4.4. Heating test 111 4.5. Sealing test 112 4.6. High-g test & drop impact test 118 5. Conclusion 125 References 128 Abstract (Korean) 136Docto

Design and fabrication of low-loss RF MEMS silicon switch using glass reflow

학위논문 (석사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2013. 8. 김용권.본 연구에서는 처음으로 유리를 스위치 구조재의 일부로 사용한 저손실 RF MEMS 실리콘 스위치를 제안하였다. 기존의 실리콘만을 구조재로 사용하여 제작되었던 RF MEMS 실리콘 스위치에서 접촉 금속 부근 구조재를 유리로 대체한 새로운 형태의 RF MEMS 실리콘 스위치를 본 연구를 통해 설계 및 제작하였으며, 접촉 금속 부근의 구조재로 실리콘보다 RF 특성에 적합한 유리를 사용함으로써 향상되는 신호 손실 특성을 이론적인 분석과 시뮬레이션을 통해 예측하고, 이를 측정 결과와 비교하였다. 제안된 유리가 구조재로 삽입된 실리콘 스위치는 5 ~ 30 GHz 의 주파수 대역의 신호에 대해 0.12 ~ 0.33 dB 수준의 삽입 손실을 보여 기존의 실리콘 스위치보다 최대 0.26 dB (0.38 ~ 0.54 dB), 그리고 고저항 실리콘을 구조재로 사용한 스위치보다 최대 0.19 dB (0.31 ~ 0.46 dB) 정도 삽입 손실이 향상된 결과를 보였다. 본 연구에서 제안하는 새로운 형태의 RF MEMS 실리콘 스위치의 제작은 유리 재용융 (Glass reflow) 공정을 기반으로 한 SiOG (Silicon On Glass) 공정으로 제안되었으며, 제안된 공정을 통해 유리 구조재가 삽입된 스위치를 성공적으로 제작하고, 스위치의 정상적인 정전 구동을 확인함으로써 제안된 공정의 유효성을 검증하였다. 한편, 낮은 삽입 손실을 가지는 RF MEMS 스위치는 실제 RF 응용에 사용될 경우 시스템에서 신호 손실 및 왜곡을 보상하기 위한 추가 회로를 줄일 수 있도록 하여 시스템의 복잡도와 비용을 줄이는 동시에 시스템의 크기도 줄일 수 있는 장점과 직결된다. 또한, 보다 낮은 손실을 가지는 RF MEMS 스위치의 개발은 기지국 안테나나 방위 체계 산업, 인공위성 교환망 등과 같이 엄격한 성능 요구 조건을 가지는 고주파 응용 분야들로의 RF MEMS 스위치 적용을 촉진시킬 것으로 기대된다. 따라서, 저손실 RF MEMS 스위치의 개발은 다양한 RF 응용에서 RF MEMS 스위치의 활용도를 높이는 데 이바지할 수 있다.In this paper, we firstly propose a novel low-loss RF MEMS silicon switch which utilizes reflowed glass as a switch structure near the contact metal. A new concept of electrostatically-driven RF MEMS silicon switch was presented and realized through the proposed fabrication process. By introducing reflowed glass into the silicon switch structure, the substrate loss induced by switch structure has greatly reduced. To verify the enhancement in loss characteristic, we fabricated 3 different types of RF MEMS silicon switches (silicon-, high resistance silicon-structured switch, and the proposed switch) and measured their insertion losses. In the frequency range of 5 to 30 GHz, the proposed RF MEMS switch with reflowed glass inside the switch structure showed insertion loss of 0.12 ~ 0.33 dB, while silicon- and high resistance silicon-structure switch showed 0.38 ~ 0.54 dB, 0.31 ~ 0.46 dB, respectively. Before fabrication, theoretical analysis and simulations were carried out to predict the enhancement in insertion loss brought by the introduction of the reflowed glass. The expected improvement in the insertion loss characteristic of proposed RF MEMS switch was greater than 0.1 dB, compared to the conventional RF MEMS silicon switch. Proposed fabrication method of the novel RF MEMS switch was based on SiOG process, assisted with the glass reflow process. The proposed fabrication process was validated with successful fabrication of the proposed switch. We believe that the proposed fabrication process could be used for a wide range of RF MEMS area where low-loss characteristic is needed. Low insertion loss characteristic of RF MEMS switch can contribute to reduce not only the complexity and cost, but also the size of the system by eliminating additional circuitry for loss compensation in the system. Therefore, it can be said that development of low loss RF MEMS switch can widen RF application fields where RF MEMS switch can be used. Furthermore, with this enhanced loss characteristic, RF MEMS silicon switch is expected to be used in the RF applications of strict performance requirement, such as base-station antenna, defense system, satellite switching network, etc.초록 i 목차 iii 표 목차 v 그림 목차 vi 제 1 장 서론 １ 1.1 연구의 배경 １ 1.2 RF MEMS 스위치의 연구 동향 ４ 1.2.1 RF MEMS 스위치 ４ 1.2.2 RF MEMS 스위치의 응용 분야 ８ 1.3 연구의 동기 및 목적 １２ 1.4 논문의 구성 １４ 제 2 장 유리 재용융 공정을 이용한 저손실 RF MEMS 실리콘 스위치의 이론과 설계 １６ 2.1 RF MEMS 실리콘 스위치가 제작된 CPW 전송 선로의 기판 손실 분석 １６ 2.2 CPW 전송 선로의 설계 ２２ 2.3 스위치 구조의 설계 ２７ 2.3.1 스위치의 접촉부 영역 설계 ２７ 2.3.2 스위치 구조물 및 스프링의 설계 ２９ 2.3.3 스위치의 구동 전압 특성 예측 ３１ 2.3.4 스위치의 신호 전송 특성 예측 ３５ 제 3 장 유리 재용융 공정을 이용한 저손실 RF MEMS 실리콘 스위치의 제작 ３８ 3.1 전체 제작 과정 ３８ 3.2 단위 공정 ３９ 3.2.1 유리 재용융을 이용한 실리콘 기판의 제작 ３９ 3.2.2 CPW 전송 선로 제작을 위한 유리 기판의 제작 ４９ 3.2.3 실리콘-유리 기판의 접합 및 Release 공정 ５７ 3.3 제작 결과 ６０ 제 4 장 유리 재용융 공정을 이용한 저손실 RF MEMS 실리콘 스위치의 특성 측정 ６５ 4.1 스위치 구동 전압 특성 측정 ６５ 4.2 스위치 신호 전송 특성 측정 ６９ 제 5 장 결론 ７６ 참고문헌 ７８ ABSTRACT ８２Maste

Studies on spontaneous and stimulated emission in photonic bandgap cavities

학위논문(박사) - 한국과학기술원 : 물리학과, 2000.8, [ vii, 140 p. ]한국과학기술원 : 물리학과