Zhi-Jian Li

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.

Design of a new PZT based microphone and microspeaker

Abstract A new Pb(Zr0.53Ti0.47)O3 (PZT) based cantilever structure composed of Pt/Ti/PZT/Pt/Ti/SiO2/Si3N4 multilayer is designed for integrated microphone and mirospeaker. The cantilever structure is theoretically studied and designed using a multimorph model. The properties of the PZT-based and ZnO-based cantilevers are compared.

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.

Study of a Ferroelectrics-Silicon Integrated Microspeaker and Microspeaker Array

ABSTRACT A novel ferroelectrics-silicon integrated microspeaker and microspeaker array is proposed. The Al/SiO2/Pt/Pb(Zr,Ti)O3/Pt/Ti/SiO2 multimorph structure is designed and fabricated. The microspeaker based on this multimorph structure has high output acoustic pressure, and the displacement at the center of membrane is very high. This structure designed in the single microspeaker can also be used in microspeaker array. After optimization of the position of the electroacoustical transducer cells, the realized microspeaker array can reach the high output acoustic power and good transducing directivity. This integrated microspeaker and microspeaker array will be widely used for audio frequency and ultrasonic frequency devices.

An improved behavioral model of ferroelectric capacitors

Abstract An improved behavioral model for ferroelectric capacitors is proposed successfully. This model gives accurate simulation results for FeRAM writing and reading process, which helps to the optimization of FeRAM circuit design. The model can also be adapted to express the P-V characteristic of a FE capacitor imposed by nonsymmetrical voltage.

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.

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

Study of Bi2TI2O7-based metal-ferroelectric-semiconductor (MFS) FET

Abstract P-channel metal-ferroelectric-semiconductor field-effect-transistors (MFSFETs) and MFS capacitors using Bi2Ti2O7(BTO)/Si(100) structures were fabricated. The film stoichiometry and structure lattice are verified using X-ray energy dispersion analysis (EDAX) and X-ray diffraction (XRD). The C-V and other characteristics the devices showed good hysteresis loops with memory window as large as 4V under ±5V sweeping.