Jiunnjye Tsaur

Fabrication of Optical Micro Scanner Driven by PZT Actuators

We have designed, simulated, fabricated and tested microelectromechanical system (MEMS) based one-dimensional (1D) optical micro scanners driven by piezoelectric actuators. The designed micro scanners have a micro mirror (1 mm ×1 mm) supported by rotation bars connected to hinges and piezoelectric cantilevers. Pt/Ti/PZT/Pt/Ti/SiO2/SOI multi-layered structure was subjected to MEMS fabrication to form the micro scanners. Through the fabrication, we have obtained 3 types of scanners with 5, 10 and 20 µm-wide hinges. The resonant frequency corresponding to a torsional mode was measured to be 4100, 5563 and 6025 Hz, respectively. We also compared the optical scanning angle of the micro scanners actuated at the resonant frequency. The micro scanner with 10 µm-wide hinge actuated at 5563 Hz showed the widest scanning angle. The scanning angle reaches 25 deg at the actuation voltage of 20 V.

Preparation and Application of Lead Zirconate Titanate (PZT) Films Deposited by Hybrid Process: Sol-Gel Method and Laser Ablation

Among the many ferroelectric film fabrication techniques, the sol-gel process provides high purity, large deposition area and easy composition control. However, the thickness limit of a crack-free single-layer film is about 0.2 µm and about 10 times of coating and thermal treatment processing are needed to deposit 1.5 µm-thick films. In laser ablation, the deposition rate is expected to be 1–2 µm/h, but the film quality is lower than that deposited by the sol-gel method. In this work, the hybrid process, involving the sol-gel method and laser ablation, was used to make 1.65 µm-thick lead zirconate titanate (PZT) films with well-crystallized perovskite phase at the (111) orientation. We deposited (111)-oriented 0.15 µm-thick PZT film on Pt/Ti/SiO2/Si substrates using the sol-gel method and then deposited 1.5 µm-thick PZT films by laser ablation. The remanent polarization of 28.6 µC/cm2 and the coercive field of 58.0 kV/cm were obtained while the dielectric constant and loss values measured at 1 kHz were approximately 1050 and 0.045, respectively. The piezoelectric coefficient d31 was also investigated and found to be 16.65±4 pC/N. In the application, a micromirror actuated by the hybrid PZT films was designed and fabricated successfully by a three-mask lithography process. The scanning angle of 6±2 degrees was demonstrated, while resonating with 5 Vp-p at the resonance frequency (1975 Hz).

Design and Fabrication of 1D and 2D Micro Scanners Actuated by Double Layered Lead Zirconate Titanate (PZT) Bimorph Beams

Micro scanners including 1D scanner beams and 2D scanning micromirrors are designed and fabricated. In order to yield large bending force, the sol-gel derived double layered lead zirconate titanate (PZT) structures are developed to be the actuator components. In our developed fabrication process, the use of thermal treatment and the addition of one platinium/titanium film played an important role to yield the well-crystallized perovskite phase and decrease the residual strss of total cantilever structures successfully. In the case of 1D scanner beams with the size of 750×230 µm2, the optical scanning angle was 41.2 deg with respect to actuation with AC 5 V at 2706 Hz. Under the applied bias of 10 V, the bimorph beam bended upward and the deflection angle of 34.3 deg was measured. A 2D scanning micromirror supported by four suspended double layered PZT actuators was designed to rotate around two orthogonal axes by the operation at different resonant frequencies. While resonating with AC 7.5 V at 3750 Hz and 5350 Hz, the maximum scanning area of 24°×26° was obtained.

Investigation of TMAH for front-side bulk micromachining process from manufacturing aspect

Abstract An investigation on the influence of etchant concentration, dissolving silicon content and additives during silicon anisotropic etching in tetramethyl ammonium hydroxide (TMAH) has been carried out. Based on the Taguchi method, the etch rates of Si, Al, and SiO 2 were measured via under-etch experiments using the wagon-wheel mask pattern. The improvement on the surface quality was observed by agitating the solution under ultrasonic vibration in TMAH solutions with additives. Furthermore, a new approach is developed to reduce wet etching time and to control etched gap depth between the released micromembrane and the silicon substrate. This method employs a polysilicon or an amorphous silicon thin layer embedded between the micromembrane and silicon substrate as a sacrificial layer, then this layer would be fast isotropically etched away by TMAH solution.

2D micro scanner actuated by sol-gel derived double layered PZT

2D micro scanners actuated by sol-gel derived double layered PZT actuators were designed and fabricated. In our previous work, the better scanning capability of double layered PZT structures has been investigated. The purpose of this paper is to determine 1D and 2D scanning characteristics of 2D micro scanners with respect to resonant actuations. While resonating with 7.5 V at 3750 Hz and 5350 Hz, the scanning angle of 26/spl plusmn/2 degrees and 24/spl plusmn/2 degrees were obtained. Furthermore, the new fabrication process greatly improved the residual stress of suspended structures due to the compensation effect of double layered PZT. Wet etching process for PZT not only amended the uniformity, but also increased the device yield economically.

Fabrication and performance of a flat piezoelectric cantilever obtained using a sol–gel derived PZT thick film deposited on a SOI wafer

The present paper reports on the fabrication and performance of flat piezoelectric cantilevers obtained using a sol–gel derived PZT thick film deposited on a SOI (semiconductor-on-insulator) wafer. Highly (100) oriented PZT thick films (2.7 µm) have been deposited onto the SOI wafer with a Pt/Ti layer and an SiO2 layer (Pt/Ti/SiO2/Si/SiO2/Si multi-layered structure hereafter) by the sol–gel technique. The upper SiO2 layer between the Pt/Ti bottom electrode and upper Si layer was found to play an important role in avoiding breaking the Pt/Ti bottom electrode. The dielectric constant and the remanant polarization of the deposited PZT films were measured as 1250 and 17 µC cm−2 respectively. The transverse piezoelectric constant (−d31) estimated from these data is 117 pC N−1. After coating the Pt/Ti top electrode on the PZT layer, microfabrication techniques were used on the Pt/Ti/PZT/Pt/Ti/SiO2/Si/SiO2/Si multi-layered structures to form piezoelectric cantilevers. The resulting cantilevers composed of Pt/Ti/PZT/Pt/Ti/SiO2/Si multi-layered structures were found to be flat. The transverse piezoelectric constant (−d31) of the PZT thick films calculated from the measured displacement of the cantilevers is 84–132 pC N−1. The present data are 4–5 times larger than our previous data. This may be due to low stress in the PZT thick film achieved by using the Si layer of the Pt/Ti/SiO2/Si/SiO2/Si multi-layered structure as a structural material.

Residual Stress Study of SiO2/Pt/Pb(Zr,Ti)O3/Pt Multilayer Structure for Micro Electro Mechanical System Applications.

Stresses in micro electro mechanical system (MEMS) multilayer structures with SiO2/Pt/Pb(Zr,Ti)O3/Pt thin-film stacks on Si substrates were investigated by measuring the radius of wafer curvature for each film. The SiO2 film and Pt electrodes were under compressive stress and Pb(Zr,Ti)O3 film was under tensile stress prior to subsequent depositions. However, the stresses in each film after the last coating were tensile, except in the Pt top electrode. The interactions between different films in the multilayer were also studied by measuring the radius of curvature as each film was wet-etched layer by layer. Furthermore, the beams were fabricated using a microfabrication process to investigate the curving state of a multilayer structure released from the Si substrate. The curving states of beams are related to not only the stresses in each film but also the balance of flexural rigidity among films. A beam without any curvature was successfully obtained by adjusting the thickness of each film.

Preparation and characterization of PZT thin films deposited by pulsed laser deposition on template layer

Abstract Pb(Zr x Ti 1− x )O 3 thin films were prepared by pulsed laser deposition using the target of Pb(Zr 0.45 Ti 0.55 )O 3 with excess PbO (20 wt.%) on Pt/Ti/SiO 2 /Si(100) substrates with and without a template layer derived by the sol-gel process. Crystalline phases and microstructure of the PZT films were investigated using X-ray diffraction analysis and scanning electron microscopy, respectively. The electrical properties of the PZT films were evaluated by measuring the polarization versus electric field hysteresis loop and the dielectric constant. In comparison with the experimental results, it was found that the template layer derived by the sol-gel process could effect the crystallographic orientation, and improve the electrical properties of the PZT films. It is clear that 1–3 μm thick films with good electrical properties can be fabricated by the pulsed laser deposition process on the template layer in a shorter time.

Development of 1D Optical Micro Scanner Driven by Piezoelectric Actuators

1D optical micro scanners driven by piezoelectric actuators have designed, simulated, fabricated and tested. The newly designed micro scanners have a structure that rotation bars, hinges and PZT cantilevers support a square mirror (1mm × 1mm). Flat-structured micro scanners have been fabricated from Pt/PZT/Pt/Ti/SiO2 /SOI(Si/SiO2 /Si) multi-layered structure through conventional MEMS micro fabrication technologies. The micro scanner driven at 10 V showed an optical scan angle of 1.5 degree for the static actuation (60 Hz) and of 13 degree for the resonant actuation (4825 Hz), respectively.Copyright

Sol-gel deposition of PZT thick film on Pt/Ti/SOI substrate and application to 2D micro scanning mirror

The present study reports the sol-gel deposition of PZT thick films on Pt/Ti/SOI substrate and its application to the micro cantilevers and 2D micro optical scanning mirrors. Crack-free PZT thick films (2.7 µm) have fabricated on Pt/Ti/SOI substrate. Thin SiO2 layer on the top of the SOI substrate was found to play important role as a burrier layer to avoid breaking the Pt/Ti bottom electrode layer. The micro cantilevers and 2D micro scanning mirrors fabricated by MEMS technologies are flat suggesting the advantage of using SOI substrate instead of Si substrate. The deflection of the tip of the 800 µm-long x 250 µm-width micro cantilever was measured to be 5.9 µm at 5 V. The absolute value of the transverse piezoelectric constant |d31| of the PZT thick film calculated from the deflection is as high as 84 pC/N. The scan angle of the cantilever via resonant actuation at 2387 Hz is as high as 40 degree with only 6 V (peak-to-peak). The response time of micro cantilevers were measured to be within 0.3-1 ms. These data indicate the potential application of the present 2D micro scanning mirrors to wavelength division multiplexing (WDM) systems driven at several voltage.