Cai Bing-chu

A MEMS-Based Piezoelectric Power Generator for Low Frequency Vibration Energy Harvesting

A novel power generator has been achieved to convert vibration to electrical energy via the piezoelectric effect. The generator obtained by micro fabrication process mainly consists of silicon based frame and composite cantilever. The prototype tested at resonant vibration generates 1.15 μW of effective power to a 20.4-kΩ resistance load. The potential of this work is to offer miniaturization solutions for power generators, and with the proposed method the ambient ubiquitous vibration can be harvested effectively as endless energy source to form an integrated self-powering system.

Multiple-State Storage Capability of Stacked Chalcogenide Films (Si16Sb33Te51/Si4Sb45Te51/Si11Sb39Te50) for Phase Change Memory

The multiple-state storage capability of phase change memory (PCM) is confirmed by using stacked chalcogenide films as the storage medium. The current–voltage characteristics and the resistance–current characteristics of the PCM clearly indicate that four states can be stored in this stacked film structure. Qualitative analysis indicates that the multiple-state storage capability of this stacked film structure is due to successive crystallizations in different Si–Sb–Te layers triggered by different amplitude currents.

Nitrogen and Silicon Co-Doping of Ge2Sb2Te5 Thin Films for Improving Phase Change Memory Performance

Electrical properties and phase structures of (Si+N)-codoped Ge2Sb2Te5 (GST) for phase change memory are investigated to improve the memory performance. Compared to the films with N or Si dopants only in previous reports, the (Si+N)-doped GST has a remarkable improvement of crystalline resistivity of about 104mΩcm. The Fourier-transform infrared spectroscopy spectrum reveals the Si–N bonds formation in the film. X-ray diffraction patterns show that the grain size is reduced due to the crystallization inhibition of the amorphous GST by SiNx, which results in higher crystalline resistivity. This is very useful to reduce writing current for phase change memory applications.

Improvement of Electrical Properties of the Ge2Sb2Te5 Film by Doping Si for Phase-Change Random Access Memory

Si-doped Ge2Sb2Te5 films have been prepared by dc magnetron co-sputtering with Ge2Sb2Te5 and Si targets. The addition of Si in the Ge2Sb2Te5 film results in the increase of both crystallization temperature and phase-transition temperature from face-centred-cubic (fcc) phase to hexagonal (hex) phase. The resistivity of the Ge2Sb2Te5 film shows a significant increase with the Si doping. When doping 11.8 at.% of Si in the film, the resistivity after 460°C annealing increases from 1 to 11 mΩ.cm and dynamic resistance increase from 64 to 99Ω compared to the undoped Ge2Sb2Te5 film. This is very helpful to writing current reduction of phase-change random access memory.

CONSTRAINTS AND RESOLUTION FOR PHASE CHANGE MATERIALS AND MEMORY DEVICE SCALING

ABSTRACT The electrical properties, especially the resistance of GST resistor for PRAM (Phase-change RAM) application, are investigated when its size downscales to 10 or 20 nm. It is shown the downscaling of the phase-change materials to nanometer leads to increasing resistance. However, for PRAM arrays, process variation and increasing sub-threshold leakage current of access transistor (AT) together with other factors such as complex peripheral circuits come unsolved before PRAM can be widely used. Herein experimental and theoretical results show that there is no limit to downscaling before 45 nm node with many solutions being able to extend this trend.

Experimental study of noncontact ultrasonic motor with non-symmetrical electrode

We have proposed a novel noncontact ultrasonic motor based on non-symmetrical electrode driving. The configuration of this electrode and the fabrication process of rotors are presented. Its vibration characteristics are computed and analysed by using the finite element method and studied experimentally. Good agreement between them is obtained. Moreover, it is also shown that this noncontact ultrasonic motor is operated in antisymmetric radial vibration mode of B21 mode. The maximum revolution speed for three-blade and six-blade rotors are 5100 and 3700 r/min at an input voltage of 20V, respectively. Also, the noncontact high-speed revolution of the rotors can be realized by the parts of I, III of the electrode or II, IV of the electrode. The levitation distance between the stator and rotor is about 140μm according to the theoretical calculation and the experimental measurement.