Physical model for charge accumulation and technology development for robust RF MEMS switches
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- Institutt for informatikk 
AbstractRadio frequency (RF) micro-electromechanical system (MEMS) capacitive switches are expected to be a very promising technology for many microwave and wireless applications since they can provide low loss, low-power consumption, high linearity and quality factor. However, the reliability problem is still one of the important limitation factors which present a research challenge for the commercialization. The lifetime of these switches is believed to be strongly influenced by dielectric charging. In spite of huge effort has been made from many research groups worldwide for more than a decade to develop robust RF MEMS switches, little information is available in the literature providing a fundamental solution to this problem. The key challenge is to understand the principle of charge injection when the field across the dielectric layers. In this thesis, we employed a metal-insulator-semiconductor (MIS) capacitor structure to investigate the dielectric charging and discharging for high reliable capacitive RF MEMS switches. The dielectric charging and discharging kinetics were qualitatively and quantitatively characterized by comparing the measured capacitance-voltage (C-V) curves on MIS structure before and after charge injection. We firstly investigated the charging and discharging properties in Si3N4 and SiO2 single dielectric layers, respectively, e.g., the dependence of charge injection and relaxation on the stress time, magnitude, polarity of applied voltage. To explain the observed experimental results, we have proposed a generalized charge injection model and a relaxation model by taking into account the roles of holes and electrons. From the investigation of charging and discharging properties in Si3N4 and SiO2, we concluded that there are two basic approaches for mitigating charge accumulation: (1) reducing charge injection level when high stess voltage is applied and (2) accelerating charge relaxation process after the high voltage is removed. Based on the first approach, we have investigated how charge accumulates in multi-layer dielectric stacks, e.g., double- and triple-layer dielectrics. The experimental results suggest that it is possible to balance the number of charges injected from the top and bottom electrodes by optimizing the thickness ratio of Si3N4 to SiO2 in Si3N4/SiO2 double dielectric layers. Based on the second approach, we have investigated the charge accumulation in doping dielectrics, e.g., doping phosphorus or boron ions into SiNx dielectric films and doping silicon nanocrystals into silicon oxide, the experimental results indicate that it is possible to create ‘combination center’ in the dielectric for short relaxation mechanisms by doping technology.
This article is included in the thesis:
Gang Li, Haisheng San, Xuyuan Chen, “Charging and discharging in ion implanted dielectric films used for capacitive RF MEMS switch ”, J. Appl. Phys105, 124503 (2009). DOI: 10.1063/1.3147862
These articles are removed due to publisher restrictions:
(1) Gang Li and Xuyuan Chen, "Modified Fowler-Nordheim tunnelling for modelling charge injection in Si3N4 of MIS structure", Appl. Phys. A, Vol.109, 2012. DOI: 10.1007/s00339-012-7065-5
(2) Gang Li, Haisheng San, Xuyuan Chen, “Charging and discharging in ion implanted dielectric films used for capacitive RF MEMS switch ”, J. Appl. Phys105, 124503 (2009). DOI: 10.1063/1.3147862
(3) Gang Li, Ulrik Hanke, Oddvar Søråsen, Deokki Min and Xuyuan Chen, "Investigation of Charge relaxation behaviors in Si3N4 for the reliability of electrostatically driven MEMS structure", Microelectronics Reliability, in process.
(4) Gang Li, Ulrik Hanke and Xuyuan Chen, "Effect of SiO2 thickness on charge accumulation in double-layer dielectric for high reliable Capacitive RF MEMS Switch", submitted to J. Appl. Phys.
(5) Gang Li and Xuyuan Chen, "Investigation of Charge injection and relaxation in multidielectric stacks for Capacitive RF MEMS switch application", IEEE Transactions on electron devices, in process. DOI: 10.1109/TED.2013.2263252
(6) Haisheng San, Zhiqiang Deng, Yuxi Yu, Gang Li, and Xuyuan Chen, "Study on dielectric charging in low-stress silicon nitride with the MIS structure for reliable MEMS applications", J. Micromech. Microeng. 21, 125019 (2011). DOI: 10.1088/0960-1317/21/12/125019
(7) Haisheng San, Xuyuan Chen, Gang Li, Linxian Zhan “Using Metal Insulator Semiconductor Capacitor to Investigate dielectrics charging in capacitive microelectromechanical switches”, Appl. Phys. Lett. 93, 063506 (2008). http://link.aip.org/link/doi/10.1063/1.2970043 DOI: 10.1063/1.2970043
(8) Haisheng San, Lin Li, Gang Li, Xuyuan Chen, BoxueFeng, “Frequency response measurement of high-speed photodetectors using the spectrum power method in a delay self-heterodyne system”, Applied Physics B: lasers and optics 88, pp. 411-415 (2007). DOI: 10.1007/s00340-007-2702-y
(1) Gang Li, Ulrik Hanke and Xuyuan Chen, "Investigation of charge accumulation in Si3N4/SiO2 dielectric stacks for electrostatically actuated NEMS/MEMS reliability”, Chapter10, Nanoelectronics Device Application Handbook, CRC Press, in Press.
(1) Gang Li, Ulrik Hanke, Zaijun Cheng, Deokki Min, Haisheng San and Xuyuan Chen, “Si3N4/SiO2 dielectric stacks for high reliable Capacitive RF MEMS Switch", IEEE NANO 2011, Aug. 2011, Oregon, USA.
(2) Gang Li, Ulrik Hanke, Deokki Min and Xuyuan Chen, “Comparison of charge injection in SiO2 and Si3N4 for Capacitive RF MEMS switches", 2011 International conference on electronic packaging technology and high density package, Aug. 2011, Shanghai, China.
(3) Gang Li, Yingge Wang and Xuyuan Chen, “Charge accumulation in double layer dielectric for high reliable Capacitive RF MEMS Switch", 22nd Micromechanics and Micro systems Europe Workshop, June 19-22, 2011, Tønsberg, Norway.
(4) Gang Li, Haisheng San and Xuyuan Chen, "Charge accumulation and their relaxation in SiO2 films containing silicon nanocrystals ", 5th Annual IEEE Int. Conf. on NEMS, 20-23 Jan. 2010, Xiamen, Fujian, China.
(5) Gang Li, Linxian Zhan??Haisheng San, Peng Xu and Xuyuan Chen, "Effects of ion implantation on dielectric charging in PECVD silicon nitride films for RF MEMS switches application", Annual IEEE Int. Conf. on Nano/Micro Engineered and Molecular Systems (IEEE-NEMS), 6-9 Jan. 2008, Sanya, Hainan, China.
(6) Gang Li, Linxian Zhan, Haisheng San, Peng Xu, Xuyuan Chen, “Influence of Ion Implantation on dielectric charging in Capacitive RF MEMS switches”. SPIE Photonics Asia 2007, Nov. 2007, Beijing, China. x
(7) Haisheng San, Xiaoshan Zheng, Zhiwen Zhao, Gang Li and Xuyuan Chen, "Investigation of Charge relaxation of dielectrics for Capacitive Micro-Actuators", 5th Annual IEEE Int. Conf. on NEMS, 20-23 Jan. 2010, Xiamen, Fujian, China.