Ning-Xin Zhang

MICRO ACOUSTIC DEVICES USING PIEZOELECTRIC FILMS

ABSTRACT A novel PZT based micro acoustic device with the diaphragms clamped on all four edges has been studied. It can be used both as microphone and microspeaker. Compared with other piezoelectric micro acoustic devices, PZT based device has higher sensitivity for microphone and larger output acoustic pressure for microspeaker. The microfabrication process flow of this device is simple, and the transducer has excellent performance, miniature size and high reliability. The micro acoustic devices could be widely used in various practical audio frequencies and ultrasonic systems.

Novel ferroelectrics-based micro-acoustic devices and their ultrasonic applications

Novel ferroelectric thin film based micro-acoustic devices have been designed and fabricated using silicon based micro-machining process. These devices have excellent performance, miniature size and high reliability, and could be compatible with conventional integrated circuit process. And more important, they can be both used as microphone and microspeaker. The micro-acoustic devices could find wide and novel application in practical ultrasonic systems.

PMUTs for Handwriting Recognition

ABSTRACT Piezoelectric micromachined ultrasonic transducers based on PZT-coated membrane structures has been fabricated, packaged and tested. A handwriting recognition system composed of three fabricated transducers is proposed. Due to its small size and low cost, this PMUTs handwriting recognition system is extraordinary promising in portable computer, cellular phone and many other minitype digital devices.

UNIFORMITY IMPROVEMENT OF PZT BASED ULTRASONIC TRANSDUCER

ABSTRACT A PZT based micromachined ultrasonic transducer is proposed. This transducer can be used both for microphone and microspeaker. By using the temporary boron-doped silicon layer, high uniformity of the resonance frequency of transducers can be realized. Besides, choosing an appropriate thickness of the support silicon dioxide layer can minimize the residual stress of the multilayer membrane structure. These PZT based transducers with high sensitivity and high uniformity could be widely used in various practical ultrasonic systems.

DIRECTIVITY OPTIMIZATION OF PZT BASED MICROSPEAKER ARRAY

ABSTRACT In this paper, the directivity is optimized for a PZT based microspeaker array. The SiO2/Pt/Pb(Zr,Ti)O3/Pt/Ti/SiO2 multimorph structure has been designed and fabricated to be the microspeaker cell using silicon based micro-machining process. The membrane size of the single transducer cell is 1000× 1000× 2.5 μ m3, and the main resonance frequency is located near 68 kHz (λ = 5 mm). Directivity is a very important parameter for microspeaker array. Dissimilar arrangement of the cells in transducer array could cause different directivity performance. After comparison, when achieving a good transmitting directivity, the square combined plane array has the smallest area.

EFFECT OF ANNEALING TEMPERATURE ON PROPERTIES OF SPUTTERED PZT THIN FILMS

ABSTRACT Lead zirconate titanate (PZT) thin films with a composition near the morphotropic phase boundary region were fabricated on the Pt(111)/Ti/SiO2/Si(100) multilayer substrate using sputtering method. An additional annealing treatment was carried out for one minute using a rapid thermal process (RTP) in oxygen atmosphere to improve densification and crystallization. The annealing temperature effects on crystal orientations and electric properties of PZT thin films were investigated. It has been found that the PZT thin film annealed at 650°C shows the best crystalline structure and has the best dielectric and ferroelectric properties.

FABRICATION AND CHARACTERIZATION OF IN-PLANE POLARIZED PZT FILMS WITH INTERDIGITAL ELECTRODES

ABSTRACT In this paper, Pb(Zr0.53,Ti0.47)O3 films are deposited on titania by sol-gel method, and PZT films of ∼4 μm in thickness are successfully obtained by repeating multi-coating and annealing. Based on the think film deposition processing, a laminated Pt/Ti/PZT/TiO2/SiO2/Si structure is proposed, and the PZT films are in-plane polarized by top InterDigital Electrodes (IDE). The capacitance-voltage curves of the PZT thick films are measured in a range of −40 V to 40 V, and the symmetric butterfly shapes of the curves indicate good ferroelectric properties of the films. The capacitance is found dependent on the parameters of the electrode configuration, and a simple equation for predicting the IDE capacitance is deduced.

Directivity Analysis of a Novel Piezoelectric Film Based Ultrasonic Microspeaker Array

In this paper, a novel piezoelectric film based ultrasonic microspeaker array is proposed. The SiO2/Pt/Pb(Zr,Ti)O3 /Pt/Ti/SiO2 multimorph structure has been designed and fabricated using silicon based micro-machining process. The membrane size of the single transducer cell is 1000times1000times2.5 mum 3, and the main resonance frequency is located near 68kHz. The performance of directivity is a very important parameter in microspeaker array. Especially in ultrasonic applications, a good transmitting directivity of microspeaker array is indispensable. Dissimilar arrangement of the cells in transducer array could cause different directivity performance. After comparison, when achieving a good transmitting directivity, the square combined plane array has the smallest array area. In addition, the directivity patterns of different planes vertical to the microspeaker array plane are also discussed

Nondestructive evaluation of MEMS devices by laser confocal measurements

This paper proposes an innovative nondestructive evaluation (NDE) setup for MEMS mechanical deformation measurements. The setup is based on an active laser confocal displacement meter, and a computer controlled motor-driven 3-dimension (3D) stage. The out-of-plane measurement resolution of the scanning confocal setup is 0.1 /spl mu/m. The maximum measurement range is 0.3 mm out-of-plane and 60 mm/spl times/60 mm in plane, respectively. The principle of the measurement method is introduced briefly. A multilayer piezoelectric acoustic MEMS membrane was fabricated and measured by using this setup. The profile of membrane was estimated. Nonlinear response feature of the membrane to direct current bias voltage was observed. The residual stresses of individual layer of the membrane were estimated according to Stoneys theory. The test results gave quantificational description of MEMS membrane deformation, which can guide the optimal design of the acoustic devices. The laser confocal technique proved to be a valuable micro-NDE characterization tool.

Influence of Stress on the Performance of PZT Thin Films for Microphone Application

ABSTRACT A series of microphone cells based on integrated PZT thin films were fabricated by typical MEMS process. The thickness of back silicon as a load of the vibrating diaphragm was controlled by changing ICP (Inductive Coupling Plasma) etching time and power. Concaved diaphragms with different radius were formed due to the balanced tensile stress among the multi-layer films structure. The remnent and saturated polarization strength of microphone cells decreased with the increased deformation of diaphragm. The phenomenon was explained as the weakening of mechanical-electrical coupling in piezoelectric thin films in stressed state.