Zhihai Zhang

Fabrication Improvement of the Grating Light Modulator

A new type of grating light modulator (GLM) for display application has been presented. It has the advantages of the MOEMS modulator. Meanwhile, it is easy for integration of array device and reduces the fabrication complication. The modulation principle and the fabrication results are given. Some methods to enhance the quality of the GLM are proposed. To enlarge the effective optical area, the central part of GLM is thickened. And to improve the surface quality, the evaporated Al film is adopted instead of sputtered Al. In correspond to these changes, the changed fabrication flow are shown

Electromechanical Characteristic Analysis of Passive Matrix Addressing for Grating Light Modulator

A Grating Light Modulator (GLM) based on Micro-Electro-Mechanical Systems (MEMS) is applied in projection display. The operating principle of the GLM is introduced in this paper. The electromechanical characteristic of the passive matrix addressing GLM is studied. It was found that if the spring constant is larger, both the response frequency and the driving voltage are larger. Theoretical analysis shows that the operating voltage and the pull-in voltage of the GLM are 8.16 and 8.74 V, respectively. When an all-selected pixel in a m×n array is actuated by a voltage V0, the voltages of the half-selected pixel in row and column are V0(m–1)/(m+n–1) and V0(n–1)/(m+n–1), respectively, and the voltage of the non-selected pixel is V0/(m+n–1). Finally, the experimental results indicate that the operating voltage and the pull-in voltage are 7.8 and 8.5V respectively, and the response frequency of the GLM is about 7 kHz. The crosstalk in a 16×16 GLM array is validated by the experiment. These studies provide a theoretical basis for improving the GLM driver.

Analysis of Optical Collecting System for MEMS-based Grating Moving Light Modulator

Grating moving light modulator, a MEMS-based movable diffraction grating with electrostatic actuation, can be used for projection displays and relevant applications, its dominant power exchange is between the 0th and plusmn1st order by modulating phase of incident light, two optical collecting systems based on 0th, plusmn1st order operation are designed and analyzed with Fraunhofer diffraction theory and Fourier transforms optics, the latter is more available with theoretical performance of imaging system: optical efficiency eta=30.6%, contrast V=1225, comparing with the simulation results by Coventorware: eta=29.5%, V=740, the decrease results from the warp of the device when pulled down by electrostatic force

Electromechanical characteristics analysis and simulation of grating light modulator

In this paper, a 27um×27um novel grating light modulator supported by cantilevers has been presented, and it can be fabricated using silicon surface-micromachining technology. The structure and basic operation principle of grating light modulator is introduced. The structure is composed of grating plate, address electrode and four cantilevers, the grating plate, which is supported by four cantilevers placed around, is overhung about one wavelength of incidence light from the underlying address electrode, it is actuated like a piston by electrostatic force, and piston-type motion of grating can be used to modulate phase of incident light, therefore, the grating light modulator array is a potential device for projection displays and relevant devices for its intrinsic characteristics. Mechanics model is developed for deducing the deformation equation, the relationship between the electromechanical characteristics of the device and the geometrical parameters and material performance is analyzed, such as pull-in voltage, resonance frequency and step response time. Electromechanical coupled simulation is done by Coventorware, then, more reasonable geometrical parameters are obtained for fabricated in the next step.

Grating light modulator for projection display

A novel grating light modulator for projection display is introduced. It consists of an upper moveable grating, a bottom mirror, and four supporting posts between them. The moveable grating and the bottom mirror compose a phase grating whose phase difference is controlled by the actuating voltage. When the phase difference is 2k\pi, the grating light modulator will switch the incident light to zero-order diffraction; when the phase difference is (2k-1)\pi, the grating light modulator will diffract light to first-order diffraction. A 16\times16 modulator array is fabricated by the surface micromachining technology. The device works well when it is actuated by a voltage with 1-kHz frequency and 10-V amplitude. The fabricated grating light modulator can show blackness and brightness when controlled by the voltage. This modulator has potential applications in projection display system.

Characteristic analysis and study of an active matrix addressing for grating light modulator

Grating Light Modulator(GLM) based on MEMS is applied in projection display. In order to eliminate crosstalk of GLM array, a monolithic integration device of GLM and active matrix is presented with post-CMOS process. The operating principle of monolithic integration device is introduced. Active matrix unit is composed of a NMOS transistor and a capacitor. The bottom electrode of GLM is connected to the electrode of the capacitor by via, so the voltage of GLM equals to the voltage of capacitor. Every GLM unit is controlled by sole active matrix unit, so crosstalk can be eliminated, which improves optical contrast and optical utilization ratio. And, the monolithic integration process of active matrix and GLM is designed. Then the key indexes and parameters of active matrix which influences the performance of monolithic integration device are analyzed in detail. Its indicated by analysis that storage capacitor and width-length ratio of transistor influence the holding-voltage property and switch speed of monolithic integration device. Finally, with 0.18µm process design kit(PDK) of SMIC and Cadence software, layout of monolithic integration device is designed. The simulation results validate the correctness of the analyzed theory and the designed circuits. The monolithic integration device designed can be applied in projection display which has 1920×1080 resolution, 30Hz frame frequency and 256 grayscales.

Analysis and optimization for effective diffraction area of grating movable light modulator

GMLM (Grating Movable Light Modulator)is a novel light modulator based on MOEMS technology which can be used in fields of display and print. But present design has only 30% effective diffraction area, which can deeply influence the key parameters such as pixel-filling-ratio and contrast. An electromechanical model of the device was established, and the effective spring constant of GMLM was deduced by energy method. According to that the relation between structure parameters and effective diffraction area was analyzed theoretically. Then optimized structures were simulated and validated by FEM software Coveter Ware. Simulation data shows that the optimization device model can enhance the effective diffraction area to about 90% from less than 30% before optimization.