Wenjing Liu

A Tip-Tilt-Piston Micromirror With Symmetrical Lateral-Shift-Free Piezoelectric Actuators

In this paper, we present the design, fabrication, and characterization of a high-fill-factor tip-tilt-piston micromirror actuated by four symmetrical lateral-shift-free (LSF) piezoelectric actuators. Lead zirconate titanate (PZT) is the piezoelectric material deposited using a sol-gel process. The micromirror can operate in both piston and rotation modes. At the piston mode, the measured resonant frequency is 990 Hz. An 18.3-μm piston displacement is obtained by applying 5 Vdc to four symmetrical LSF (SLSF) actuators. For the rotation mode, the measured resonant frequency is 1650 Hz and an optical deflection angle of 4.2° is measured by applying 5 Vdc to one SLSF actuator. A 2-D resonant scanning pattern is achieved when the PZT micromirror is applied with a 3 Vpp sinusoidal voltage at the resonance frequency.

Tip-tilt-piston piezoelectric micromirror with folded PZT unimorph actuators

This paper presents the design, fabrication and characterization of a novel tip-tilt-piston (TTP) scanning micromirror based on an array of folded piezoelectric unimorph actuators. The micromirror can perform rotational scan around two in-plane orthogonal axes as well as out-of-plane piston motion. The measured resonant frequencies of the fabricated micromirror are 362 Hz (piston), 685 Hz (x axis scan), 1250 Hz (y axis scan) and 19.2 kHz (fast y axis scan), respectively.

Two-axis scanning micromirror based on a tilt-and-lateral shift-free piezoelectric actuator

This paper presents a 2-axis scanning piezoelectric micromirror with zero initial tilt and no lateral shift during scanning. The piezoelectric material is a sol-gel PZT with a Zr/Ti ratio of 53/47. The unimorph PZT actuation beams consist of Pt/Ti/PZT/Pt/Ti/SiO2 thin-film layers, which are released via undercutting the substrate silicon. Two-dimensional scans with a 4.8° scan range have been demonstrated at 2 V at 635 Hz (resonance).

Miniature photoacoustic imaging probe using MEMS scanning micromirror

This paper presents the design and characterization of an electrothermally actuated high-fill-factor tip-tilt-piston (TTP) micromirror and its application to three-dimensional (3D) photoacoustic imaging (PAI). The micromirror chip is 2mm × 2mm. It has large scan range (>25°) at low driving voltage (∼4V) and can perform fast raster scanning. A miniature PAI probe with a diameter of 11.5 mm has been developed. The 3D images of in vivo human blood vessels are successfully obtained using this MEMS-based PAI system.

Tip-tilt-pistion micromirror based on symmetrical lateral-shift-free piezoelectric actuators

This paper presents the design, fabrication and characterization of a high-fill-factor tip-tilt-piston (TTP) micromirror which employs four symmetrical lateral-shift-free (LSF) piezoelectric actuators. Lead zirconate titanate (PZT) is the piezoelectric material deposited using a sol-gel process. The measured resonant frequencies of the fabricated micromirror are 990 Hz (piston) and 1450 Hz (rotation), respectively. At resonance, the maximum piston motion is 92 μm and the rotational scan angle is 9.6°, both measured at a 5 Vpp sinusoidal driving voltage.

An auto-aligned vertical comb drive for low-cost variable optical attenuators

Vertical comb drives are critical for electrostatic optical switches and variable optical attenuators (VOAs), but fabricating vertical comb-drives suffers from the difficulty of dealing with the comb-finger misalignment. This paper presents a vertical comb drive design and its micro-fabrication method that can realize self-aligned two-level comb fingers. The self-aligned vertical comb fingers are enabled by a novel vertically-elevated flat-end (VEFE) bimorph structure. Both the stator and rotor fingers of the vertical comb-drive are formed by the same photomask and the same silicon etching step, which automatically ensures accurate alignment of the stator and rotor fingers. The vertical separation between the stator and rotor is created by the VEFE structure. A 1mm-aperture MEMS mirror with the proposed VEFE comb drive has been fabricated using SOI wafers with buried cavities. The mirror rotates 0.94° at 8 Vdc. The resonant frequency is 1.428 kHz. The MEMS mirror has been assembled into a VOA module. Measurements show that the VOA can achieve a dynamic range of −55 dB and an insertion loss of less than 0.4 dB.

Hysteresis Property of Tip-Tilt-Piston Micromirror Based on Tilt-and-Lateral Shift-Free Piezoelectric Unimorph Actuator

This paper presents hysteresis property of tip-tilt-piston micromirror based on tilt-and-lateral shift-free piezoelectric unimorph actuator. The accuracy and the level of performance of piezoelectric actuator will be reduced for the reason of hysteresis behavior of piezoelectric device. To compensate the hysteresis behavior of the actuator, the properties should be researched and tested at first. The paper report the hysteresis behavior of micromirror with TLSF piezoelectric actuator under fixed frequency driving is stable with respect to the changes of the time and amplitude of driving voltage without considering the failure effect.

Reliability evaluation of micromirror of double S-shaped unimorph piezoelectric actuator with probabilistic approach

This paper presents the long time reliability evaluation of a micromirror with double S-shaped unimorph piezoelectric (dSUP) actuator design using a probabilistic approach. The lifetime (number of cycles to failure) of the piezoelectric actuator, electrical strength, and electrical load are considered as the random variables; and their probability distributions are discussed. The interference model of electrical load and electrical strength is used to evaluate the reliability of dSUP actuators. By this approach, the relationship between the reliability and the lifetime of the dSUP actuator has been deduced.