Vol.1 No.2 2008

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Research paper : The aerosol deposition method (J. Akedo et al.)−125 Synthesiology - English edition Vol.1 No.2 (2008) In response to demands for “necessary amount at necessary places” or “multiple product variable volume,” we investigated the on-demand application of process and manufacturing system. Since the AD method is a nozzle spray process, it has the potential for an on-demand process similar to the ink jet technology.As case study, we investigated the application of the AD method to piezoelectrically actuated Si-MEMS optical scanner, as shown in Figure 5. This scanner is expected to be used in next-generation laser printers, barcode readers, and ITS laser radars, and will become a key component of next-generation display devices such as micro projectors and retinal projection displays. Therefore, requirements include high-speed scanning of tens of kHz, scanning angle of over 20°, millimeter size mirror, reduced distortion during motion, and low voltage drive[6].In the manufacturing process the scanner structure was formed using Si micromachining, and an active film, which would be the driving source, was coated only in required areas. Conventionally, to create such actuator structures, upper and lower electrode layer and piezoelectric layer were deposited using the sputter method, CVD method, or sol-gel method after forming the structure by bulk micromachining using wet and/or dry etching. The substrate has to be heated to crystallize the piezoelectric layer and the patterning is usually done by etching. An expensive microfabrication device, a coating device, and processes involving over 20 steps were necessary. In contrast, using the AD method, the piezoelectric layer could be formed accurately only in necessary areas of the microfabricated Si scanner structure. The etching process for piezoelectric and electrode layers became unnecessary and this enabled drastic reduction of processes and facilities along with improved coating speed. Device performance has been also improved, scanning frequency of 33.4 kHz and optical beam scanning angle of 30° were obtained, and the resulting optical scanner had higher speed and larger amplification than conventional electrostatic driven, electromagnetic driven, and piezoelectric driven MEMS optical scanners[7]. These results were possible because the thickness of the piezoelectric film was easily thickened in the process, and as a result, the generative force of drive source was increased and a Si torsion beam structure with high rigidity could be employed.4.2 Application to metal base MEMS scanner and reflection in device designBecause high performance piezoelectric film could be formed on any substrate material using the AD method, we investigated the fabrication of a metal base device for a less expensive, highly impact resistant, and practical small-size actuator[8]. Figure 6 shows the manufacturing process of Lamb wave resonance type high-speed micro optical scanner that was created by replacing Si with stainless steel Simplification of processConventional Si micro-machiningMain processMask(SiO2)SiMask(SiO2)Si①②③④⑤⑥⑦⑧⑨⑩Ti/PtTi/PtPZTPZTPtResistMask2(SiNX)Mask2Resist workIntroduction of AD methodSpin coatExposureDevelopmentResistPtPZTAu or Al①②③④⑤(Created Si-MEMS scanner)Fig. 5 Comparison of Si-MEMS optical scanner driven by AD piezoelectric film and conventional manufacturing process.SUS substrateMicro-press1 minAD methodFormation of PZT thick film5 min10 minHeat treatment at 600 °CFormation of upper electrode20 minPolarization at 40 kV/cm20 minWire splicing and fixing5 minFig. 6 Metal-base optical scanner driven by AD piezoelectric film and manufacturing process.Conventional MEMS optical scannerPZT driven metal-base optical scanner1101009080706050403020100Drive frequency (kHz)Optical scan angle x Mirror size (θD)Metal-base MEMSConventional Si MEMS051015202530354045505560Fig. 7 Comparison of performance of metal-base optical scanner based on Lamb wave resonance principle and conventional Si-MEMS scanner.(53)−

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