Process Development and Integration of Piezoelectric Aluminum Nitride Thin-Film for RF MEMS Applications
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Process Development and Integration of Piezoelectric Aluminum Nitride Thin-Film for RF MEMS Applications Rajnish K. Sharma, Jiang Ning, Feng Hanhua and R. Gopalakrishnan Institute of Microelectronics, 11 Science Park Road, Singapore Science Park II Singapore-117685 e-mail: [email protected]; Fax: 65-6777-0670 ABSTRACT: The aluminum nitride (AlN) process was successfully developed for as high frequency thin-film for bulk acoustic resonator applications. Columnar AlN was deposited on p-type (100) silicon substrate at 300-500oC using pulse direct current (DC) sputtering technique. Argon to nitrogen ratio was optimized to achieve stoichiometry at higher deposition rates of about 1000 Å/min at 14 kW DC power. The XRD of as-deposited and annealed AlN film shows preferred (002) orientations. The dry etching process was developed and etching rate about 3200 Å/min was achieved using Cl based chemistry. Film composition analysis was done using AES technique and stoichiometry was achieved. INTRODUCTION: At present there is a growing demand in high radio frequency (rf) wireless applications and this market is growing very fast for the frequency range 500 MHz to 5 GHz. The main applications in this range are wireless communication, navigation, palmtop computers, low cost GPS systems and various other forms of data communications. The requirement of high performance resonators and filters become important as number of data communicates due to many end users. Hence, the high performance resonators and filters are in demand with same package or on same chip with high frequency integrated circuits. The electro-acoustic devices such as SAW filters, bulk acoustic wave filters, sensors and actuators, oscillators, resonators and delay lines have wide applications from consumer electronics to military and space equipments. Hence, there is need to develop materials and processing technology of low cost electro-acoustic filters operating in microwave region. The MEMS based bulk acoustic resonators are small in size and can be integrated with active high frequency CMOS device. The high performance filters can be fabricated using high quality piezoelectric materials. There are many other materials that can be used as piezoelectric materials such as CdS, ZnO, PZT etc. [1,2], but these materials are not preferred for integration because of non-compatibility with CMOS technology. The aluminum nitride is a promising material which is quite useful in electronic and optical device application due to its wide band gap (6.2 eV), high dielectric strength, high thermal stability, chemical inertness, high elasticity and high thermal conductivity. In addition it serves as passivation and dielectric layer in integrated circuits, short wave length emitters and surface acoustic wave devices [3-7]. The nitride based (III-V) optical devices such as blue, ultraviolet (UV) light emitting diodes and lasers generated much interest in such kinds of materials. Since, AlN shows high thermal conductivity and large breakdown field, therefore, AlN base
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