Mems varactor paper 257


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  • Robust device: can be use in different environmental conditions (even in harsh environment) and under different applications.
  • In conventional two parallel plate structure the maximum tuning range that we can achieve is 1.5, after that further increase in voltage will cause the upper plate to collapse on the lower one, so in order to overcome this limitation extended tuning range structures or two gap capacitors [3] are used. There are various techniques to increase the tuning range such as three parallel plate configurations [4], digital varactors by using a bank of MEMS switches [5] and in place of parallel plate, lateral comb structures [6] can also be used. In this paper extended tuning range structure is constructed and analyzed. The center frequency is assumed as 2.4GHz
  • The voltage at which these plates will collapse is called as the pull-in voltage
  • Mems varactor paper 257

    1. 1. Design and Analysis of RF MEMS Varactor for Extended Tuning Range Presented by Pooja Srivastava IIIT-Allahabad
    2. 2. Outline • Introduction • MEMS • Varactor • Types of Varactor • Motivation • Varactor model • Operation principle • Varactor structure • Design parameters • Simulations and results • Conclusions • References
    3. 3. Introduction • MEMS • Micro-Electro-Mechanical-System • Integration of electrical unit, mechanical unit, sensor and actuator on the single substrate. • Varactor • Variable capacitor. • Capacitance varies with DC voltage. • MEMS Varactor: Advantages • Low power • High sensitivity • Robust device
    4. 4. Varactor Classification • Solid State Varactor: PN- junction diodes. Schottky diode. Metal oxide semiconductor (MOS) capacitor. • RF-MEMS Varactor: Interdigited capacitors. Zipping Varactor. Ferroelectric varactors.
    5. 5. Motivation • RF-MEMS device • Applications (High Frequency) • VCO • Frequency selective circuits • Amplifiers • Earlier (Solid State varactors) • PN-junction diode • Schottky diode • MOS capacitor • Disadvantages: • small tuning range • lower quality factor • Difficult ON-Chip realization
    6. 6. Parallel Plate Configuration • Limitations • Pull-in-Voltage • Maximum tuning range= 1.5 • Technique to increase the tuning range • Two gap capacitors. • Three parallel plate configurations. • Digital varactors by using a bank of MEMS switches. • Lateral comb structures in place of parallel plate. • In this paper extended tuning range structure is constructed and analyzed.
    7. 7. Varactor Model • Basic model of two parallel plate Varactor.
    8. 8.
    9. 9. Proposed Varactor Structure • Variable plate height architecture is used. Actuation point • Top plate (P1): four cantilever beam. • Material: Ni or Cu. • Bottom plate: Gold P1
    10. 10. Design Parameters Actuation electrode (plate 90µm x 90µm x 0.5µm P2) Proof mass (plate P1) Small Beam 109µm x 109µm x 2µm directly 50µm x 10µm x 2µm attached to the plate (for Actuation) Beam (For support) 100µm x 10µm x 2µm Initial gap between upper 2µm plate and actuation electrode (d1) Initial gap between upper 3µm plate and ground plate (d2)
    11. 11. Simulation And Results • Electromechanics Physics. • Voltage range:0-20 Volts • Pull in voltage: 17.8 Volts 3D plot of the deformed suspended top plate after applying DC voltage
    12. 12. C-V characteristics • Capacitance change for different applied voltages. • Voltage: 0-18 volts • Capacitance: 0.037 pF – 0.2417 pF • Cmax: 0.2417 pF @ 17.6 Volts • Tuning range: 6.53 • Capacitance ratio: 6.53:1
    13. 13. Displacement vs. Voltage Plot • Displacement between plate P1 and P2 is a function of applied voltage. • Initial plate gap: 2 µm • Gap before pull in: 1.6 µm
    14. 14. Conclusion • MEMS Varactor model for extended tuning range is developed. • Model is simulated to obtain tuning range greater than 1.5. • Sudden change in the measured capacitance is around 17.8 Volts. • Structure pull-in voltage: 17.8 volts. • Change in capacitance: 0.037pF to 0.2417pF • Plate displacement: 0.4µm (from 2µm to 1.6µm) • Cmax: 0.2417 pF • Cmin: 0.037 pF • Tuning range achieved: 6.53
    15. 15. References • J. Iannacci, A. Faes, B. Margesin, "MEMS Technology for RF Passive Components", Proc. of the 4th • • • • • • Int. Symposium on Applied Sciences in Biomedical and Communication Technologies (2011). M.Rahimi ,S.S.Jamuar , M.N.Hamidon, M.R.Ahmad and S.A.Mousavi, "The Design and Simulation of an Optimized MEMS Varactor with High Factor for RF Circuits", IEEE Int. Conf. on semiconductor Electronics, pp:161-165, 2008. A. Gallant and D Wood, "The role of fabrication techniques on the performance of widely tunable micro machined capacitors", International Journal of Sensors and Actuators, pp: 423-431, 2004. J. Z. Chang Liu, J. S. Aine, J. Chen, and S.M. Kang, “Development of a Wide Tuning Range MEMS Tunable Capacitor for, Wireless Communication Systems”, Int. conf. on Electron Devices Meeting, Technical Digest, pp: 403-406, 2000. C. L. Goldsmith, A. Malczewski, Z.J. Yao, S.Chen, J. Ehmke and D. R. Hinzel, '' RF MEMS Variable Capacitors for Tunable Filters," Int. J. RF and Microwave CAE, vol. 9, pp: 362-374, 1999. J. Yao, S. Park, and J. DeNatale, "High tuning ratio MEMS based tunable capacitors for RF communicationsapplications", Tech Dig Solid-State Sensors Actuators Workshop, pp: 124-127, 1998. Rebeiz, G. M., RF MEMS Theory, Design, and Technology, John Wiley & Sons, Inc., Hoboken, New Jersey, 2003.
    16. 16. Thank you