Piezoelectric MEMS

The power needs for MEMS devices are diverse— and batteries may not be the best choice to provide power to systems based on various types of MEMS drives. For example, magnetic drives operate at less than 1 V, but they require generating hundreds of milliamperes, which becomes a difficult challenge for batteries sized on the subcentimeter scale. The required micro- to nanoampere current levels for electrostatic and piezoelectric MEMS are feasible for batteries, but the tens to hundreds of volts that are needed will present difficulties for batteries with nominal voltages of 3 V. However, there may be a niche for batteries that would be used to power 10— 15 V drives. 

Fig. 13.6 Three approaches towards fabricating piezoelectric MEMS devices (Reprinted with permission from Tadigadapa and Mated (2009). Copyright 2009 lOP)...

Suleiman A, GuUbault GG (1984b) A coated piezoelectric crystal detector for phosgene. Anal Chim Acta 162 97-102 Tadigadapa S, Mated K (2009) Piezoelectric MEMS sensors state-of-the-art and perspectives. Meas Sci Technol 20 092001-092030... 

Murakami, S., Yoshimura, T., Satoh, K., Wakazono, K., Kariya, K., Fujimura, N., 2013. Development of piezoelectric MEMS vibration energy harvester using (100) oriented BiFeOa ferroelectric film. Journal of Physics Conference Series 476, 012007. 

The piezoelectric biosensor is a class of micro electromechanical systems (MEMS) based on the principle of measurement of changes in oscillating crystal resonance frequency due to bioreceptor and analyte interactions. In piezoelectric MEMS biosensors, the transducer is made of piezoelectric material (hke quartz) and the biosensing material is then coated on the piezoelectric material, which vibrates at the natural frequency. Piezoelectric materials have no center of symmetry and produce an electric signal when stressed mechanically (i.e., by applying some pressure on them). A crystal oscillates at a certain... 

University of Alberta. Educational Software for Micromachines and Related Technologies. Available online. URL http //www. cs.ualberta.ca/ database/MEMS/sma mems/index2.html. Accessed May 28,2009. Research groups at the University of Alberta in Canada constructed this Web resource, which discusses a variety of smart materials, including shape-memory alloys, piezoelectric materials, and electrorheological and magnetorheological fluids. 

In many microelectromechanical systems (mems) based on piezoelectric thin films, flexure is deliberately used to amplify the available displacements (or alternatively to increase the sensitivity of a sensor). For simplicity (and to keep poling and actuation voltages low), films are often poled and driven by electrodes at the top and bottom surfaces. As a result, the critical piezoelectric coefficient is often e31 j, rather than d33j [24], For the direct effect, the effective film coefficient, e3ij can be defined by... 

Spin coated copolymer films show a decrease in remanent polarisation if the film thickness [504, 505] decreases. The application of piezoelectric materials in micro-electro-mechanical systems (MEMS) or sensors makes it often necessary to decrease the lateral dimensions of the elements. Recently, Alexe et al. [506, 507] fabricated freestanding microcells with lateral dimensions down to 100 nm and heights of 110 nm from a ferroelectric PZT by direct... 

A review of micro-electromechanical systems (MEMS)-based delivery systems provides more detailed information of present and future possibilities (52). This covers both micropumps [electrostatic, piezoelectric, thermopneumatic, shape memory alloy bimetallic, and ionic conductive polymer films (ICPF)] and nonmechanical micropumps [magnetohydrodynamic (MHD), electrohydrodynamic (EHD), electroosmotic (EO), chemical, osmotic-type, capillary-type, and bubble-type systems]. The biocompatibility of materials for MEMS fabrication is also covered. The range of technologies available is very large and bodes well for the future. 

Cook-Chennault, K.A., Thambi, N., Sastry, A.M., 2008. Powering MEMS portable devices—a review of non-regenerative and regenerative power supply systems with special emphasis on piezoelectric energy harvesting systems. Smart Mater. Struct. 17, 043001. 

The dimensions of a dielectric may change when it is polarized this is the piezoelectric effect and is used in microelectromechanical systems (MEMS), sonar, and medical ultrasound imaging. 

MEMS APPLICATIONS USING PIEZOELECTRIC THIN FILMS... 

When a biological substance reacts with a sensing layer which is coated on the piezoelectric substrate, the resonant frequency of the MEMS biosensor is changed. The frequency shift is related to the mass change of the biologically sensitive membrane. 

Piazza G, Pisano AP (2007) Two-port stacked piezoelectric aluminum nitride contour-mode resonant MEMS. Sens Actuators A 136 638-645... 

Various thermomechanical microvalves have been developed with the development of MEMS fabrication technology. Thermomechanical micro valves work by converting thermal energy into mechanical deformation. Compared with other microvalves, such as magnetic microvalves, electrostatic microvalves, and piezoelectric microvalves, thermally driven microvalves have their own advantages such as simphcity of fabrication, controllable deflection... 

Other substrates that are used for MEMS include quartz, glass, and polymers. Quartz is attractive primarily because it is piezoelectric, so that it may be used as a sensor and an actuator. Quartz is, however, more difficult to micromachine than silicon. Pyrex glass is used in conjunction with silicon wafers, primarily for packaging, because of its optical transparency and close match in coefficient of thermal expansion (GTE). Polymers such as polycarbonate have been adopted as substrates for microfluidics because of their low cost channels require large areas, which makes silicon too expensive, and channels can be fabricated in polymers inexpensively by hot embossing. The advantages offered by silicon substrates are not required because microfluidic devices typically do not have complex... 

The most common macroscopic actuators are motors. Electromagnetic motors do not operate efficiently at the microscale, but alternative actuation mechanisms become favorable. In conventional MEMS, other types of actuators have been used to generate movement, such as electrostatic actuators, thermal actuators, piezoelectric crystals, SMAs, and magnetic actuators. 

Lee HC, et al. Piezoelectrically actuated RF MEMS DC contact switches with low voltage operation. IEEE Microwave and Guided Wave Lett 2005. 

Keywords Piezoelectric, thick film, MEMS, microsystems. 

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