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  are used. There are various techniques to increase the tuning range such as three parallel plate configurations , digital varactors by using a bank of MEMS switches  and in place of parallel plate, lateral comb structures  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
Design and Analysis of RF
MEMS Varactor for
Extended Tuning Range
• Integration of electrical unit, mechanical unit, sensor and actuator on the
• Variable capacitor.
• Capacitance varies with DC voltage.
• MEMS Varactor: Advantages
• Low power
• High sensitivity
• Robust device
• RF-MEMS device
• Applications (High Frequency)
• Frequency selective circuits
• Earlier (Solid State varactors)
• PN-junction diode
• Schottky diode
• MOS capacitor
• small tuning range
• lower quality factor
• Difficult ON-Chip realization
Parallel Plate Configuration
• 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.
Basic model of two parallel plate Varactor.
Proposed Varactor Structure
• Variable plate height architecture is used.
• Top plate (P1): four cantilever beam.
• Material: Ni or Cu.
• Bottom plate: Gold
Actuation electrode (plate 90µm x 90µm x 0.5µm
Proof mass (plate P1)
109µm x 109µm x 2µm
directly 50µm x 10µm x 2µm
attached to the plate (for
Beam (For support)
100µm x 10µm x 2µm
Initial gap between upper 2µm
Initial gap between upper 3µm
plate and ground plate (d2)
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
Displacement vs. Voltage Plot
• Displacement between plate P1 and P2 is a function of applied
• Initial plate gap: 2 µm
• Gap before pull in: 1.6 µm
• 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
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