MEMS mirrors for automotive applications

2017 IEEE International Meeting for Future of Electron Devices, Kansai (IMFEDK), 29-30 June 2017.Microelectromechanical system devices are widely employed in automotive electronics because of its low cost, small size and high functionality. Cars are going to be equipped with optical components, especially micromirrors to realize intelligent safety, driving and communication systems. The mechanical reliability of the micromirrors should be addressed, which is discussed in this manuscript

Mechanical reliability of silicon microstructures

In this article, an overview of the mechanical reliability of silicon microstructures for micro-electro-mechanical systems is given to clarify what we now know and what we still have to know about silicon as a high-performance mechanical material on the microscale. Focusing on the strength and fatigue properties of silicon, attempts to understand the reliability of silicon and to predict the device reliability of silicon-based microstructures are introduced. The effective parameters on the strength and the mechanism of fatigue failure are discussed with examples of measurement data to show the design guidelines for highly reliable silicon microstructures and devices

Ionic Liquid Electrospray Thruster with Two-Stage Electrodes On Glass Substrate

2023 IEEE 36th International Conference on Micro Electro Mechanical Systems (MEMS), 15-19 Jan. 2023.This paper reports ion emission of an ionic liquid electrospray thrustor with two-stage electrodes made on glass substrate having through hole for low-cost micro/nano satellites. By using the two-stage electrodes, one for ion extraction and the other for acceleration, high and stable ion emission and propulsion force is obtained. The emitter array was fabricated on a silicon wafer and the electrodes were fabricated on both sides of a glass substrate. The ion emission test was conducted, and the emission current was observed successfully. Almost no ions were collected on the accelerator electrode and reached to the collector electrode, which demonstrates the advantage of the two-stage configuration

Thermomechanical noise of arrayed capacitive accelerometers with 300-NM-gap sensing electrodes

2017 19th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS), 18-22 June 2017.Thermomechanical noise of arrayed capacitive accelerometers with sub-micrometer sensing electrodes was evaluated. The unit accelerometer of the array was 80-μm square, designed as a proportional scale-down of a conventional single-axis accelerometer. Since the size effect shows the capacitance sensitivity per unit volume increases by proportional downsizing, a 10-by-10 array of the one-tenth sized unit accelerometer would have the same sensitivity of a single accelerometer of same occupied area. However, the thermomechanical noise needs to be controlled and reduced by vacuum encapsulation because size reduction causes noise increase. By measuring the electrical impedance at the resonant frequency, the damping coefficient was estimated using electrical equivalent circuit modeling. The estimated thermomechanical noise was reduced below 3 μg√VHZ by encapsulating at 100 Pa, which is low enough for instrumentation applications

Zernike generation with MEMS deformadle mirror actuated by electrostatic piston array

2018 IEEE Micro Electro Mechanical Systems (MEMS), 21-25 Jan. 2018.We report a low-voltage and large-displacement electrostatic deformable mirror for in vivo retinal imaging by adaptive-optics optical coherence tomography. The mirror utilizes an electrostatic piston actuator which allows bottom electrodes to move vertically to keep the gap small to maintain large actuation force at low actuation voltage. An 8-mm-diameter mirror device was fabricated from two components; the mirror part and the actuator part. The parts were assembled with 7-μm-gap defined by an SU-8 layer. We successfully demonstrated operation of the mirror in various Zernike modes

Fracture behavior of single crystal silicon with thermal oxide layer

This paper reports on the effect of oxidation on fracture behavior of single crystal silicon (SCS). SCS specimens were fabricated from (1. 0. 0) silicon-on-insulator wafer with 5-μm-thick device layer and oxide layer were thermally grown. Quasi-static tensile testing of as-fabricated, oxidized and oxidized layer removed specimens was performed. The fracture origin location transited from the surface to silicon/oxide interface and inside of silicon. The transition may be caused by surface smoothing, thickening oxide layer and formation of oxide precipitation defects in silicon during oxidation. The radius of the oxide precipitation defects was estimated, which is well agreed with the fracture-initiating crack sizes

Electrostatic Micro Mirror Array with Batch-Fabricated Torsion Beam of Silicon Nanowire

2020 IEEE 33rd International Conference on Micro Electro Mechanical Systems (MEMS), 18-22 Jan. 2020.A new design of arrayed micro mirror device for a high performance spatial light modulator of high resonant frequency, large deflection angle with high mechanical reliability has been proposed. The mirror has 100-μm square plate of 5 μm thick, which is suspended by thin silicon nanowire of about 1 μm thick and wide. The device was fabricated using Bosch process and isotropic plasma etching. We successfully demonstrated array operation of 4×4 devices at relatively low actuation voltage (~20 Vpp) and large mechanical deflection amplitude (~9°). However, the deviation of vibration amplitude was large among unit resonators. By fitting the frequency response to the Duffing equation we found that self-enhancing actuation force caused by nonlinearity of the vertical combs was a main reason

Piezoelectric Disk Gyroscope Fabricated With Single-Crystal Lithium Niobate

A piezoelectric disk gyroscope fabricated with a single-crystal lithium niobate (LN) wafer has been developed for inertial navigation systems for localization during automated driving. LN has a high electromechanical coupling coefficient and a resonator made of a low-cost single-crystal wafer shows a high quality factor, which is suitable for high-performance vibratory gyroscopes. In this study, its crystallographic anisotropies in both in elastic and piezoelectric properties were considered to realize mode matching in the two-wine-glass-mode vibration of a disk resonator. We chose a 155°-Y-cut LN wafer because we found that its elastic compliance is uniform in any in-plane direction. Its anisotropic piezoelectric properties were considered to optimize the electrode design to oscillate the wine-glass modes efficiently. A 25.8-mm-diameter, 330- μm-thick disk resonator with 16 electrodes on each side was designed and fabricated by photolithography and grinding. The as-fabricated LN disk resonator was successfully oscillated in two wine-glass modes with a small frequency split of 0.7% at 95 kHz resonant frequency. Gyroscope operation was successful and the scale factor was 0.35 μV/°/s without any preamplifier

A New Design of Mode-Matched (100) Silicon Ring Gyroscope with Chamfered Rectangle Springs Immune to Fabrication Error

2023 IEEE International Symposium on Inertial Sensors and Systems (INERTIAL), 28-31 March 2023In this report, we proposed a new design of mode-matched (100) single crystal silicon (SCS) ring gyroscope immune to fabrication errors. The robustness against dimensional and orientation errors was confirmed by finite element analysis simulations and frequency response measurements. The designed ring resonator has a ring of uniform width suspended by eight identical suspension structures and it has eight-fold symmetry. The in-plane elastic asymmetry of the ring is compensated by the carefully designed suspension structures with four rectangular beams with two chamfered corners in each. As a simulation result, we found that the optimum chamfering size for the ring width of 5.1 μm and the diameter of 2 mm and the ring resonator is almost insensitive to fabrication errors. The resonators were fabricated using silicon-on-insulator wafers and the as-fabricated device shows small mismatch about 0.5 - 1.5%, which is caused by the nonuniform fabrication errors. After electrostatic tuning, gyro output was successfully measured

Nanometer Order Separation Control of Large Working Area Nanogap Created by Cleavage of Single-Crystal Silicon Along {111} Planes Using a MEMS Device

Nanogaps with a large working area and a precisely controlled separation of about 1 to 20 nm has important applications in nano photonics, thermal management, power generation, chemical sensing, etc. However, an effective method of fabricating such nanogaps has not yet been established. In addition, it has been necessary to evaluate the dependence of physical characteristics of nanogaps on the separation, but it has been technically and economically difficult to develop such a system. In this study, we developed a MEMS device, which can produce nanogaps with a large area and parallel smooth surfaces by the (111) plane cleavage of a single crystal silicon beam and can change and measure the separation of nanogaps. Using this device, nanogap fabrication by cleavage and separation control were uninterruptedly carried out while maintaining the cleanliness of the gap surfaces in vacuum; a nanogap with a large smooth surface area of 30 μ m² was successfully controlled in the range of 14 nm–1.5 μ m. For a small separation of less than 100 nm, the control resolution was sufficiently high at 1 nm. This method is fully compatible with conventional fabrication technologies for not only MEMS but also other semiconductor devices and should contribute to the fabrication of devices that exhibit useful quantum effects with only minor modifications. 2022-007