Novel Materials for MEMS
Monday, April 10, 2000 1:30 PM in Room Atlas Foyer
H2-2-1 Ferroelectric and Antiferroelectric Films for MEMS Applications
B. Xu, L.E. Cross (Pennsylvania State University); J.J. Bernstein (The Charles Stark Draper Laboratory)
In this talk we will introduce several types of ferroelectric and antiferroelectric thin (thickness < 1 µmm) and thick thin (thickness > 1 µmm) films we have developed for microsensor, microactuator, and microtransducer applications in microelectromechanical systems (MEMS). Ferroelectric (FE) lead zirconate titanate (PZT) films of up to 12 µmm in thickness have been prepared on Pt-coated Si substrates, which allows for the conventional, through-thickness polarization, and of up to 5 µmm in thickness on insulating layer (ZrO@sub 2@) passivated Si substrates, which allows for the novel, in-plane polarization. The in-plane poled film makes it possible to develop d@sub 33@-mode rather d@sub 31@-mode bending devices, which leads to immediate two-times improvement in device performance because d@sub 33@ = 2 d@sub 31@. It also can greatly increase the voltage sensitivity of bending devices because the film thickness and electrode spacing are independent variables in this type of film and thus smaller film capacitance can be obtained by using wider electrode spacing even for fixed film thickness. As an example for MEMS applications, micromachined, unimorph-type high frequency transducer arrays have been constructed based on both types of the PZT films, which can be used in hand-held diver's sonar system, medical ultrasound imaging, and nondestructive test. The results indicate that the voltage sensitivity of the transducer array made from the in-plane poled PZT film can be 30dB higher than that of the array made from the through-thickness poled film. In addition to PZT FE films, we have also developed antiferroelectric (AFE) films as an alternative for high-strain microactuators. The strain level of the AFE films can reach more than 0.4% (the strain level in PZT films < 0.1%), and both digital and analog actuation can be realized by modifying the compositions of the films. Applications of these high-strain AFE films in MEMS devices are now being explored.
H2-2-3 Growth and Characterisation of TiNi Shape Memory Alloy Thin Films for MEMS Applications
S.T. Davies (University of Warwick, United Kingdom); K. Tsuchiya (Ibaraki University, Japan)
The development of novel, functional, thin films for MEMS applications is becoming increasingly important. In particular, the shape memory effect exhibited by certain metal alloys is a promising candidate for exploitation in micro-scale devices. Combining microelectronic and micromechanical functionality appears to be a real possibility, thus opening up new areas of application. @paragraph@ We report the use of an ion beam sputter deposition (IBSD) process for growth of TiNi shape memory alloy (SMA) thin films and investigate growth of films with near-equiatomic composition. The IBSD process uses argon ions with energies in the range 1000 - 1500 eV produced by a Kaufman-type ion source. Current densities in the range 0.1 - 1 mA cm@super-2@ allow highly controllable growth conditions to be established with deposition rates controllable within 1 atomic layer s@super-1@. Non-alloyed targets of high purity titanium and nickel are used. Both sputtering targets and substrates are remote from the discharge plasma and deposition occurs under good vacuum of ~ 10@super-6@ mtorr thus producing high quality films. Furthermore, the ion beam energetics allow deposition at relatively low substrate temperatures. Typically these are < 150 @super o@C and as-deposited films exhibited shape memory properties without high temperature annealing, which is invariably required in processes such as d.c. or r.f. magnetron deposition. In the latter case, temperatures of 500 - 700 @super o@C are required during annealing which are incompatible with many MEMS fabrication processes. @paragraph@ The SMA films were characterised by electrical, x-ray and thermal measurements. Applications as microactuators and micropositioners, driven under closed loop control by direct Joule heating, in MEMS devices are discussed.
H2-2-4 Silicon Carbide Microelectromechanical Systems
M. Mehregany, C. Zorman, S. Guo (Case Western University)
Technical advances over the last decade has transformed the field of solid-state transducers (sensors and actuators) into what has become known as microelectro-mechanical systems (MEMS). In the most general form, MEMS consist of mechanical microstructures, microsensors, microactuators and electronics integrated in the same environment (i.e., on a silicon chip). Since MEMS presently relies on silicon technology, a key limitation is in applications characterized by >350C temperatures, chemically-reactive media, and/or mechanically-erosive flows. Silicon carbide (SiC) semiconductor technology provides an enabling capability to fabricate MEMS for such harsh environment applications. An overview of the state-of-the-art in SiC MEMS technology will be presented.