Development of high performance electrostatic microshutter with high opening ratio

Abstract

Microshutter is a MEMS-based device that controls the light path through an aperture. Since its role is the same with the liquid crystal and two polarizers, the microshutter could not have found its position in the display filed. To take a role in the future display industry, the mciroshutter must shows its superior feature that LC cannot achieve. As a solution, we propose that the microshutter has very high opening ratio so that the microshutter panel becomes highly transparent transmissive type display device. To realize high opening ratio, we concluded that the microshutter have out-of-plane angular move-ment. Since the microshutter had to move 90 degrees angularly, we proposed the new design called “part-division design.” The new design concept enables the microshutter moves 90 degrees under low operation voltage. The new microshutter has two part

one is the shutter part which is metal plate and the other is an actuation part which is bimorph cantilever actuator. Elextrostatic bimorph cantilever actuator has two major problems to utilize. One is that there is only two stable states, and other is that it has low electrical reliability due to dielectric charging effect. To over-come limited stable states problems, a patterned bottom design was proposed and demonstrated that the bimorph cantilever showed four stable states. Also, to prevent contact of the dielectric layer and bimorph cantilever which induces dielectric charging, a new design for non-contact actuator is firstly proposed and demonstrated that the life time of the bimorph cantilever is increased from 10 cycles to 100,000 cycles. A new design, part-division design, of microshutter is introduced and demonstrated. The microshutter has 70% of opening ratio which is the highest value reported ever. The response time of the microshutter was measured as $400 \mu s$. Also, stepwise actuation of the microshutter was successfully realized by the patterned bottom design. Array operation of the mciroshutter has demonstrated and shows the higher opening ratio than the single device. To enhance the opening ratio of the microshutter panel, the dead area of the single device was effectively covered by the adjacent microshutter device in the array design. As a result, the microshutter ar-ray showed the feasibility to have 90% of opening ratio. By achieving 90% of opening ratio, the mciroshutter panel can be adapted to the transparent display area where the LC based display device cannot reach. The research guides the way of MEMS based display device like microshutter to the distinctive area where their unique features are utilized.