Kemiao Jia

An Electrothermal Tip–Tilt–Piston Micromirror Based on Folded Dual S-Shaped Bimorphs

This paper presents the design, optimization, fabrication, and test results of an electrothermally actuated tip-tilt-piston micromirror with a large optical aperture of 1 mm. The fabrication of the device is a combination of thin-film surface micromachining and bulk silicon micromachining based on silicon-on-insulator wafers. The device has 3-DOF of actuations, including rotations around two axes in the mirror plane, and out-of-plane piston actuation. The micromirror shows an optical scan range of plusmn30deg about both x- and y-axes and displaces 480 mum in the z-axis, all at dc voltages that are less than 8 V. Dynamic testing of the micromirror shows that the thermal response time of each actuator is about 10 ms. Resonant frequencies of the piston and rotation motion are 336 and 488 Hz, respectively. The unique structural design of the device ensures that there is no lateral shift for the piston motion and no rotation-axis shift for the rotation scanning. With the large tip-tilt-piston scan ranges and low driving voltage, this type of device is very suitable for biomedical imaging and laser beam steering applications.

A Low-Power Low-Noise Dual-Chopper Amplifier for Capacitive CMOS-MEMS Accelerometers

This paper reports a novel dual-chopper amplifier (DCA) and its application to monolithic complementary metal-oxide semiconductor-microelectromechanical systems accelerometers. The DCA design minimizes the power consumption and noise by chopping the sensing signals at two clocks. The first clock is a high frequency for removing the flicker noise while the second clock is a significantly lower frequency to keep the unit gain bandwidth low. A monolithic three-axis accelerometer integrated with the DCA on the same chip has been successfully fabricated using a post-CMOS micromachining process. The measured noise floors are 40 μ g/√Hz in the x - and y -axis and 130 μ g/√Hz in the z -axis, and the power consumption is about 1 mW per axis.

High-Fill-Factor Micromirror Array With Hidden Bimorph Actuators and Tip–Tilt-Piston Capability

This paper presents the design, fabrication, packaging, and characterization of a novel high-fill-factor micromirror array (MMA) actuated by electrothermal bimorphs. In this paper, 4 × 4 MMA devices with an 88% area fill factor at normal incidence, 1.5 mm × 1.5 mm subaperture size, and single-crystal-silicon-supported mirror plates have been fabricated based on a single silicon-on-insulator wafer, without additional bonding/transfer processes. The bimorph actuators are hidden underneath the mirror plates, which are also protected by silicon walls. The MMA devices can directly be surface mounted onto driving circuit chips or printed circuit boards after fabrication. The subapertures can generate large tip-tilt-piston scanning and can individually be addressed. Static characterizations of the packaged devices show that each subaperture can achieve a piston stroke of ~310 μm and optical deflection angles greater than ±25° in both the x- and y-axes, all at 8-V dc. The preliminary laser-steering optical-phased-array capability of the obtained MMA device has also experimentally been demonstrated. This paper is based on the conference proceedings presented at the 23rd IEEE International Conference on Micro Electro Mechanical Systems (MEMS 2010), Hong Kong.

A CMOS-MEMS Gyroscope Interface Circuit Design With High Gain and Low Temperature Dependence

This paper describes an interface circuit design for monolithic CMOS-MEMS gyroscopes, based on a novel differential difference amplifier (DDA) with high gain, low temperature and process dependence, low noise, and low power consumption. The DDA achieves a 4 fF equivalent transcapacitance with a 0.01%/°C temperature variation. The DDA-based interface circuit has been integrated with a z-axis gyroscope on a foundry CMOS chip. A 4.5 zF/√Hz input-referred noise is achieved at 2 kHz, with a total power consumption of 4.25 mW. The gyroscope is fabricated with a post-CMOS bulk micromachining process and the device achieves a sensitivity of 1.2 mV/°/s and a noise floor 0.05 °/s/√Hz.

An improved low-power low-noise dual-chopper amplifier for capacitive CMOS-MEMS accelerometers

This paper reports an improved low-power low-noise dual-chopper amplifier (DCA) for capacitive CMOS-MEMS accelerometers. The new DCA employs an on-chip band-gap voltage reference to reduce the number of bonding pads and the complexity of the external circuits. The temperature drifting of the first-stage gain is reduced by using PMOS instead of NMOS as an active load. A prototype DCA with a three-axis accelerometer has been fabricated using the TSMC 0.35 mum technology. The number of required bonding pads is reduced from 21 to 14, and the temperature sensitivity is reduced from 1.2 times 10-3/degC to 5.4 times 10-4degC.

An Electrothermal Micromirror with High Linear Scanning Efficiency

An electrothermal micromirror with an aperture size of 1 mm times 1.2 mm has been developed. The mirror can tilt as much as 21deg with a 15 V DC voltage. High linear scanning efficiency is obtained by using a special drive voltage waveform. The waveform is characterized by two parameters which are determined experimentally.

Single-wafer solution and optical phased array application of micro-mirror arrays with high fill factor and large sub-apertures

This paper reports the fabrication and characterization of high-fill-factor micro-mirror arrays (MMAs) with large sub-apertures (i.e., mirror pixels). The MMAs are fabricated by a single-wafer fabrication process without any wafer bonding/transfer processes and are directly surface-mountable after the fabrication. A fabricated 4×4 MMA achieves a combined optical aperture of 6.4mm× 6.4mm with ∼90% fill factor and ≪±25° scan range in both x- and y- rotational axes. Preliminary optical-phased-array beam steering results are also demonstrated.

A monolithic inertial measurement unit fabricated with improved DRIE post-CMOS process

This paper reports a monolithic CMOS-MEMS inertial measurement unit (IMU), which is composed of a 3-axis accelerometer, a Z-axis and a lateral-axis gyroscope. The IMU is integrated with interface circuits on a 5×5mm2 foundry CMOS chip and fabricated with an improved DRIE post-CMOS bulk micromachining process. The new process incorporates a metal deposition to provide a thermal path for isolated structures during DRIE etching. The X/Y-axis accelerometer achieves a sensitivity of 191mV/g with a noise floor of 35µg/√Hz, and those parameters of the Z-axis are 124mV/g and 56µg/√Hz, respectively. The Z-axis gyroscope has a sensitivity of 0.3mV/°/s and a noise floor of 0.2°/s/√Hz. The characterization of X/Y-axis gyroscope is ongoing.

A 2.8-MM imaging probe based on a high-fill-factor MEMS mirror and wire-bonding-free packaging for endoscopic optical coherence tomography

This paper reports a miniature optical coherence tomography (OCT) probe and high-resolution 3-D OCT imaging results obtained with this side-view probe. The probe is only 2.8 mm in diameter, enabled by a unique high-fill-factor electrothermal MEMS mirror with hidden actuators and a novel wire-bonding-free packaging technique. The MEMS mirror has a large mirror aperture of 1 mm with a chip size of only 1.55 mm × 1.7 mm × 0.5 mm. The fabricated device achieves large 2-D scan optical angles up to 46° at only 4.8 V. The specific time-domain OCT system utilized is detailed, and the assembled side-view probe demonstrates multiple high-resolution 3-D OCT imaging results that demonstrate detailed images of a mouse ear and images detecting the presence of tumor cells, and the contrast with a normal tissue is qualitatively analyzed.

Dental optical coherence tomography employing miniaturized MEMS-based imaging probe

This paper presents the design, implementation and experimental result of a prototype MEMS-based probe for chair-side real time dental optical coherence tomography (OCT) imaging application.