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
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. 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.
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. 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. 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
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. 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. 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.
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
