Research On Micro-Scanner Based On Piezoelectric Actuator

Compared with the traditional display technologies (CRT display technology, flat panel display technology, projection display technology, etc.), micro-display technology has characteristic such as the small chip to realize a large image, extremely portable, integrating with the display driving circuit chip, so with advantages of a small volume of a portable, low cost, low power consumption.Typical applications for micro-display technologies include portable miniature projection systems (Pico-Projector), near-eye display systems, automobile prospects display systems and so on. Currently micro-display technology based on MOEMS devices has great potential for development, and the MOEMS devices of piezoelectric materials has significant advantage of fast response and low power consumption. In this thesis, the research is focus on how to meet the requirement of micro-display applications with piezoelectric micro scanning mirror device.First, the fundamental model of piezoelectric actuator is theoretically analyzed and unimorph structure is the better for the consideration of cost and difficulty of manufacturing. It can be found that:l.for the unimorph piezoelectric actuator, the optimal choice of the piezoelectric material is lead zirconate titanate material and a perovskite structure is needed; 2.Elastic layer material should choose silicon dioxide; 3. To achieve the maximum deflection angle and the highest energy conversion efficiency, the ratio of the corresponding material thickness is 0.94; 4. the driving voltage electric field should parallel to the direction of polarization of the piezoelectric material, whch drive the highest efficiency.Second, the fabrication and etch process of the silicon piezoelectric film is optimized to achieve the requirement of above theoretical analysis. For the preparation process, the research focus on control of the components ratios, perovskite structure formation and the layer stress control techniques.High-quality silicon-based ferroelectric thin film under high temperature is realized and meet the design requirements of ideal device.0.8 micron piezoelectric film has been successfully prepared. For the etch process,The problem of drilling of wet etching solution is solved, which will be combined with the dry etching to etch the PZT film to improve the etching efficiency to save the cost and reduce the damage to the ferroelectric film of the dry etching.Tests showed that such improvements over Sol-Gel method can get high performance piezoelectric thin film, can meet the requirement of ratio of zirconium titanium, perovskite structure, polarization direction, and film substrate during fabrication of unimorph piezoelectric actuator, and have excellent ferroelectric and dielectric qualities.Third, a new type of piston tilting micromirrors with double-S-shaped unimorph piezoelectric actuator is designed and fabricated, which can be applied to micro endoscopic imaging system and other lower resolution display systems. Its advantage is that the power consumption is significantly reduced while the response speed is improved for the reason that the electric drive mode is changed from thermal driving method to the piezoelectric driving method. Piston and rotary mode resonant frequency of this device is 2.45 kHz and respectively 3.5 kHz. Mirror area is 1.1 mm×1.1 mm, the resonant scanning angle under 2V amplitude sine wave driving at a pair of actuators can reach 9.65 degrees. Power consumption is about 74.3 1uW.Fourth, in order to meet the high refresh rate, high resolution of laser projection display applications, a new single scan micromirror based on piezoelectric unimorph actuator array is designed and fabricated. The new structure use the coupling principle to overcome disadvantages of low Young’s modulus of the piezoelectric unimorph beam and to obtain a high operating frequency. In order to obtain larger displacement under the same driving voltage conditions and to get greater freedom, this design will combine three sections of PZT unimorph piezoelectric beam and the three sections of silicon beam together to form a folding PZT piezoelectric unimorph actuator, which can get a greater vertical displacement using the collapsible amplification mechanisms of the bending angle. The two drives group are arranged symmetrically, so that the crimp stress of the array is symmetrical, can offset the lateral displacement shift of the mirror plate. Piezoelectric layer is a PZT thin film of 0.8μm, the elastic layer is a silicon oxide film of 0.85μm. Micromirrors can produce two-dimensional scanning and the piston movement of an outer surface. The resonant frequency of the scanning is 362 Hz (piston),685 Hz (X-axis scanning),1250 Hz (Y-axis scanning), and 21.2 kHz (quick scan), the scan angle is about 9.8 degrees at resonance, and power consumption is about 584.8μW, which has met the requirements of SVGA high-definition display system application.