基于MEMS的不同类型的谐振器

MEMS is a micro-electro-mechanical system. It has actively developed into research and development in a broader range of  applications, such as in analog system, switches, and in communication system, such as in the oscillator, filter part of RF  transceivers.MEMS resonator have potential to replace the available technologies like quartz crystal resonator, LC filters, ceramic filter,  SAW filters. There are different types of MEMS resonator such as clamped free resonator ,clamped-clamped resonator, free-free resonator,  disc resonator. MEMS resonators can be utilized to meet the increasing count of RF components likely to be demanded by the next  generation multi-band/multi-mode wireless devices, as it needs less area, less power consumption, less material.

MEMS are a micro electro mechanical system. They have  been developed since the 1970s.They are essentially miniature  devices that use a mechanical movement. MEMS consist of  mechanical, electrical systems whose order of size in microns.  It is a technology used to miniaturize systems. Resonator is a  system that having resonant behaviour, Resonance is a phenomenon where a system shows selective response at specific  frequencies. The resonance occurs when the system is capable  of storing energy and also Capable of transferring energy from  one mode to another. Depending upon the principle of operation the resonance may occur in different domain like mechanical, electrical, electromagnetic, optical, acoustic etc. For example, in mechanical domain the system may vibrate with greater amplitude at some frequencies than the other. The frequency at which the system oscillates with greater amplitude is  known as resonant frequency. MEMS are widely used by  systems in high (3–30MHz) ,very high (30– 300MHz) and even  ultra-high (300 MHz–3GHz) frequency ranges .They provide a  promising alternative to traditional electronic components  especially for RF devices (e.g. mixers, tunable capacitors, inductors, switches, oscillators). From the industrial perspective,  these technologies promise exactly what their applications  need be, that is, high-capability devices and systems with  portability and low power consumption. The use of these elements integrated into a single silicon chip, along with the  CMOS circuitry, will improve the performance of systems  with added benefits of reduced costs, power consumption and  size.Based on beam position there are different types of resonator such as clamped free resonator , clamped-clamped resonator, free-free resonator.

According to A. Zainuddin, etal, it uses both clamped-clamped & clamped free resonator & gives comparison pts of both in terms of reso nance frequency and pull in voltage. Fig 1shows electrical  set up for both resonators. The clamped-clamped resonator requires maximally 10v DC voltage, while clamped  free resonator requires 7.5v. For clamped-clamped the  resonance frequency for mode1 is 19.42MHZ, for mode223.87MHZ. For clamped free resonator the resonance frequency for mode1 is 2.92MHZ and for mode2 is 3.68  MHZ. The lower pull in voltage values for clamped free  structure show its potential to be applied in low power  devices.

Fig1

With reference to  Yongmei Zhao, etal, it gives idea of the clamped-clamped  filter. Figure 3.shows Perspective schematic of the SiC-based  clamped-clamped filter.It uses two anchors & two beam coupled with coupling beam. As coupling beam position change  and size of the resonator beam changes the frequency & BW  changes. The effect of the coupling beam on the bandwidth of  the filter was analyzed by FEA .

The study in the paper shows the design of clamped free beam  resonator based on MEMS. Based on the discussion made above  it is found that upto now, the designed resonance frequency for  clamped free structure is 2.92MHZ & for that required Pull in  voltage is 7.5v, but for some wireless standards such as GSM, IS- 95, Bluetooth &RF transceiver requires high resonance frequency  So, there is a need of high resonance frequency greater than 3MHZ & reduction in pull in voltage less than 7.5v.