Applications of Laser Processing for Sensors and Actuators
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The fabrication of sensors and actuators requires new materials with multicomponent stoichiometry as well as new three-dimensional microstructures. We present several potential applications of laser processing for the fabrication of sensors and actuators. The first example concerns gas sensors which require ionic conductor multicomponent ceramics whose stoichiometry is not maintained by conventional sputtering methods. We have successfully employed pulsed laser deposition (PLD) for producing high quality NASICON (Na SuperIonic CONductor) thin films. XPS measurements show that all elements are transferred from a target of Nal+xZr2SixP3-xO12, (where 0 < x < 3 ) to the substrate, and that the composition of the thin film is very close to that of the target. Electrical measurements show good ionic conductivity.
Thus,
these films
are suitable
for the
fabrication
of
electrochemical gas sensors. Since such ceramic thin films are very sensitive to liquids, wet etching is prohibited, and patterning is done using laser ablation. For other applications, a laser micromachining technique has been developed to make tunnels and cavities in Si under SiO 2 films, based on the laserinduced C12 etching of Si and high chlorine Si/Si0 2 etch rate ratios. Tunnels with length of up to 3 mm and cavities of 100xl00 gm 2 were successfully fabricated in Si0 2 /Si bilayer samples. These are usable in microfluidic or gas pressure measurement systems. INTRODUCTION
The field of sensors and actuators is rapidly expanding, due to potential applications in the automotive, manufacturing automation, communication, biomedical and air conditioning industries. The principal types of sensors measure pressure, flow, temperature, position, acceleration and gas composition[l. According to recent studies, microsensors will proliferate rapidly, generating revenues of as much as $10 billions annually by the year 2000 [2]. Conventional microelectronics technologies developed in the last decades have limitations for the fabrication of new types of sensors and actuators, which often require multicomponent thin films or combinations of thin films for sensing elements, as well as three-dimensional microstructures. 305
Mat. Res. Soc. Symp. Proc. Vol. 397 © 1996 Materials Research Society
It is now well recognized that the main obstacle to the rapid growth in this field is the lack of manufacturing know-how, which has been adapted in the past from the semiconductor technology on a case-by-case basis [2]. Lasers offer interesting characteristics for processing materials. Opportunities for laser processing in the field of sensors and actuators are very large. High quality multicomponent thin films can be made by pulsed laser deposition (PLD) with properties often superior to those obtained by any other fabrication technique [3]. Moreover, directing a laser beam onto a substrate allows us to micromachine this material and to produce microstructures which are difficult, or sometimes, impossible to make by other means [4-6]. We present here an overview of some
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