This paper characterises a novel Chemical Mechanical Polishing (CMP) based process for the fabrication of
nanometer wide transducer gaps for RF MEMS resonators. The process requires one photolithographic step
less than previously reported fabrication methods and does not super from transducer gap widening, which
otherwise strongly affects the impedance of manufactured resonators. CMP test masks were used to evaluate
the ability to produce nanometer wide planarised capacitive transducer gaps and to determine the planarity
of CMP based processing. As a result of this work, pattern dependent removal rates for polysilicon have been
determined and design guidelines defined to optimise the yield of CMP fabricated resonators.
An optical workstation consisting of a surface profiler, laser vibrometer and a high power pulsed laser has been constructed for mechanical testing of MEMS. Through a series of static and dynamic measurements, the performance of a device is determined in seconds. For these measurements the device is induced to move by either using mechanical, electrostatic or optical actuation methods. In the latter case this is achieved by directing high power light pulses onto a silicon surface. The same laser can also be used to trim and frequency tune resonant devices. The workstation has been designed to incorporate single devices, wafers and packaged devices so that devices may be characterised at any stage of processing. The speed and non-contact nature of this workstation makes it suitable for industrial metrology. A variety of MEMS have been characterised, examples of which are presented. The workstation has also proved to be an invaluable tool for determining the cause of device failure in prototype designs.
The application of biotelemetry in the case of a RF controllable microvalve is discussed. Biotelemetry implies the contactless measurement of different electrical and nonelectrical parameters measured on human or animal subjects. A biotelemetry system consists of a transmitter and a receiver with a transmission link in-between. Transmitted information can be a biopotential or a nonelectric value like arterial pressure, respiration, body temperature or pH value. Transducers convert nonelectrical values into electrical signals. Radio frequency (RF) telemetry allows a patient greater mobility. Above all, the application of wireless communication becomes more and more popular in microinvasive surgery. Battery powered implants are most commonly used, but batteries must be changed after a period of time. To avoid this, wireless transcutaneous radio frequency (RF) communication is proposed for the powering and control of medical implants.
In this paper, we consider the novel concept of a Radio Frequency (RF) controllable microvalve for different medical applications. Wireless communication via a Surface Acoustic Wave Identification-mark (SAW ID-tag) is used to control, drive and locate the microvalve inside the human body. The energy required for these functions is provided by RF pulses, which are transmitted to the valve and back by a reader/transmitter system outside of the body. These RF bursts are converted into Surface Acoustic Waves (SAWs), which propagate along the piezoelectric actuator material of the microvalve. These waves cause deflections, which are employed to open and close the microvalve. We identified five important areas of application of the microvalve in biomedicine: 1) fertility control; 2) artificial venous valves; 3) flow cytometry; 4) drug delivery and 5) DNA mapping.
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