Bulk Silicon MEMS Research Articles

Silicon-based waveguide technology for millimeter-wave antennas

This paper describes a method for the preparation of complex structured waveguides that can be used for millimeter-wave antennas based on a bulk silicon MEMS process. In this paper, a millimeter-wave band array of ridge waveguide slit antennas with multilayer step-matched feeds is realized by this method. A bulk silicon MEMS process is used to realize the complex structure and the high precision and flatness requirements on the millimeter scale, which cannot be achieved by machining. And the step height difference of more than 100um is realized by combining multiple lithography and silicon oxide mask. The step difference is larger than that achievable by dry etching using the etching selection ratio of silicon oxide and silicon. The waveguide fabricated by this method can work well in the millimeter wave band and is used for antenna feeding, power distribution, etc. It is characterized by compact structure, high precision, and high performance.

Design of a High-Gain Hybrid Slot Antenna Array Based on Bulk Silicon MEMS Process for W-Band Applications

A W-band, high-gain, hybrid slot antenna array based on bulk silicon MEMS technology is proposed in this paper. The high-order-mode cavity is explored to excite the 2 × 2-slot basic unit, so as to reach the low-profile requirement of the bulk silicon MEMS process. To avoid the fragile structure of the large-scale antenna arrays based on the bulk silicon MEMS process, the ridge gap waveguide is employed to build the feed network for a large-scale array. A vertical transition between a rectangular waveguide and a ridge gap waveguide is designed to support the low-loss and low-cost assembling method between the radiation units and the feed network. An 8 × 8-slot hybrid antenna array is simulated and fabricated. The measured results show a relative bandwidth (VSWR < 2) of 8.1% with the first side-lobe level less than −11 dB over the frequency band of 91–97 GHz. A maximum gain of 26.1 dBi with the radiation efficiency of 65.2% is achieved. With high gain and high fabrication efficiency, the proposed hybrid slot antenna array would be valuable for W-band radar applications.

Analytical study and compensation for temperature drifts of a bulk silicon MEMS capacitive accelerometer

An analytical study and a compensation structure for temperature drifts of bias and scale factor of a bulk silicon MEMS capacitive accelerometer are presented. The analytical model for the temperature drift of bias (TDB) and temperature drift of scale factor (TDSF) is established based on the analysis results of thermal deformation and stiffness temperature dependence. The model shows that TDB is only caused by thermal deformation, while TDSF consists of two parts caused by stiffness temperature dependence and thermal deformation, respectively. The two parts are positive and negative, respectively, but the second part has greater absolute value. First part of TDSF can be reduced by high doping. TDB and second part of TDSF can be both reduced by soft adhesive die attaching or increasing substrate thickness. In silicon structure, TDB can be reduced by middle-locating anchors for moving electrodes in sensitive direction or decreasing the stiffness asymmetry of springs, while second part of TDSF can be reduced by middle-locating anchors for fixed electrodes in sensitive direction. By middle-locating anchors both for moving electrodes and fixed electrodes, a temperature compensation structure is designed to reduce TDB and second part of TDSF. Consequently, TDSF is reduced by making the two parts of TDSF cancel each other. Experimental results show that TDB is suppressed from 1.85mg/°C to 0.52mg/°C, while TDSF from −162.7ppm/°C to −50.8ppm/°C.

A Micro-Machined Silicon Vibrating Ring Gyroscope

The presented work focuses on the design, fabrication and frequency characteristics of a multi-mass MEMS vibrating ring gyroscope. After modal and harmonic simulation in ANSYS, the first 12 modes’ resonant frequencies and impacts on the sense-axis displacement are obtained. This gyroscope is fabricated through the silicon-on-glass process and deep etching bulk silicon MEMS technology. With a view to obtain the frequency characteristics, the authors attempt set of frequency sweeping experiment, whose record agrees well with ANSYS simulation results. The preliminary experimental data present the relationship between drive voltage and resonant characteristics and indicate that the structural design of vibrating ring and multi-mass can effectively depart the operational modes away from the interfering modes with a higher Q of sense axis at atmospheric pressure.

Thermal drift analysis using a multiphysics model of bulk silicon MEMS capacitive accelerometer

An interpretation of the thermal drift of the bulk silicon MEMS capacitive accelerometer using multiphysics analysis is proposed in this paper. Stress, strain, electrostatics, thermal and structural interactions are simulated based on the finite element method. The thermal drift is generated by both the stiffness asymmetry of the U-springs of the structure and relative displacement caused by the mismatch in thermal expansion coefficients between the Pyrex glass substrate and heavily boron-doped silicon structure, neither of which is dispensable. Although the layout design is symmetrical, the asymmetric widths of the U-springs, which cause stiffness asymmetry, are observed by scanning electron microscopy. To achieve a fast and feasible simulation, we divide the model into two components with different configurations. During the simulation, boundary conditions are carefully set up according to the fabrication process. A series of experiments is designed to verify the result, including a temperature experiment from −40 to 100 °C and DC voltage polarity experiment. To verify the conclusion, a new layout design that gradually increases the width of the U-springs without changing any other dimension is simulated, fabricated, and tested. The simulation and experiment results are compared and discussed.

Far-field evanescent wave propagation using coupled subwavelength gratings for a MEMS sensor

A technique was developed to couple near-field evanescent waves into observable diffraction orders in the far-field region. This investigation was of two gratings that have a 1.0 microm grating period in glass and 1.1 microm in silicon and are individually subwavelength, but when coupled together yield an 11.0 microm effective grating period. This effective grating period is not subwavelength to a 1.550 microm infrared incident source and exhibits higher diffraction orders. Optimum evanescent wave coupling efficiency was simulated by varying the grating thickness and the grating separation between the subwavelength gratings. This proposed evanescent wave coupling concept is being investigated for use in a bulk silicon MEMS accelerometer.

On line measurement of maximal torsional strength of micro level structure

In the design and fabrication of microelectronic system(MEMS)devices, the process based on silicon is a main technolog which draws great attention of researchers. Bonding technology including silicon to glass and silicon to silicon is fundamental for bulk silicon MEMS devices.For MEMS devices, the bonding area is from the micrometer to millimeter scale, thus traditional methods to test bonding strength are no longer feasible. Measuring the strength at that scale has become the bottle-neck for MEMS development. We first define a new way, with which a series of single crystal cantilever beam was taken to test the maxal shear stress of bonding strength in the micro area.The experiment gives curves of torsional strength versus the bonding area and torsional strength versus the probe movement distance, the designer can use them to determine the bonding area according to the required torque for their MEMS devices.