| As one part of the typical MOEMS, the micro-spectrometer has many advantagescompared with traditional spectrometers. It can be used in many areas. For these reasons,research on the MOEMS spectrometer has become one of the research focuses inworldwide.Based on the previous research works on the MOEMS mirror andrefraction-diffraction hybrid integrated micro spectrometer, the basic theories of gratinghave been further studied. The final goal of this study is to fabricate a MOEMSgrating integrated with an angle sensor. The primary coverage is listed as following.①In this paper, a scheme of novelMOEMS scanning phase grating integrated withthe angle sensor is put forward. The difficulties in the fabrication of such MOEMSdevice have been analyzed. This MOEMS scanning grating is driven by theelectromagnetic force. The purpose of this design is for increasing the Signal-to-Noiseof output signal and reducing the size of near infrared spectrometer by using MOEMSgrating.②We have shown the device operation principles and some design parameters.Simulations of device tuning versus applied voltage performed on a particular prototypeshowed that the device could give high resolution angle tuning. Meanwhile, theparameter of the electromagnet angle sensor is designed. Diffraction efficiency isdesigned and optimizing. We used Fourier optical theory and diffraction optical theoryanalyzed the diffraction efficiency of the rectangular phase grating, and used thePCGrate simulated the design. After analysis and calculation, we found the bestparameter for efficiency of the grating.③According the model, the fabrication process and mask was designed andfabricated. Prototypes were fabricated using LPCVD, wet etching, electroplating, RIEand DRIE process which requires the much time for beat fabrication condition.Therefore, minimal residual stress, excellent optical flatness, and high integrationflexibility are achieved simultaneously. In future runs, the DRIE and the releasing stepswill be optimized to ensure that all residues are cleaned up before testing. Last, forfurther test of the device, the silicon silt was fabricated.④Measured tuning characteristics (tuning angle against applied voltage) using twodifferent methods agreed well with each other and also with the theory. The frequency response of the device was measured and peaked at600.385Hz, which can be mademuch higher after redesigning the flexure stiffness. The tested torsion range of ourfirst-generation device was5.51583degree with0.0668V actuation. However, the testedtorsion range should be larger if we improve the driving voltage; the main reason forthis problem is the test method. Anyway, the deflection angle which we tested satisfiesour needs, this is not a fundamental limit for the device.⑤I n order to investigate the characteristics of theMOEMS grating, measurementswith two NIR interference filters with wavelength of880nm and904nm have beenperformed. Spectrum is captured with a number of1024measure points per screen ofthe oscillograph. However, the data is sampled and averaged for reduce the effect of thenoise which in the output signal and reduce the SNR of the useful signal. As the gratingrotates with a high frequency of, the spectrum can be captured within only1msec.Averages of1024measurements or more are no problem because of the good stabilityof the rotation frequency. The required measurement time remains still short.⑥Given both the simulation and experimental results and the obtained experiencein fabrication processes, we expect, conservatively, a next-generation device with Au/Crsputtered as optical surface will improve the diffraction efficiency. In principle, byreplacing the reflection material Al with gold and optimizing the parameter of thestructure, a high-efficiency (40.5%) reflection phase grating can be realized. This devicewill be applied for applications such as spectrometer, in which diffraction efficiency andaperture requirement is critical. |
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