Chen Pei-Yi

High-Density Stacked Ru Nanocrystals for Nonvolatile Memory Application

Stacked ruthenium (Ru) nanocrystals (NCs) are formed by rapid thermal annealing for the whole gate stacks and embedded in memory structure, which is compatible with conventional CMOS technology. Ru NCs with high density (3 × 1012 cm−2), small size (2–4 nm) and good uniformity both in aerial distribution and morphology are formed. Attributed to the higher surface trap density, a memory window of 5.2 V is obtained with stacked Ru NCs in comparison to that of 3.5 V with single-layer samples. The stacked Ru NCs device also exhibits much better retention performance because of Coulomb blockade and vertical uniformity between stacked Ru NCs.

Nonvolatile Memory Characteristics with Embedded High Density Ruthenium Nanocrystals

Ruthenium (Ru) nanocrystals (NCs) embedded in SiO2 gate stacks are formed by rapid thermal annealing for the whole gate stacks and embedded in the memory structure, which is compatible with conventional CMOS technology. The devices exhibit a substantial and clockwise hysteresis in capacitance-voltage measurement. The Ru NCs exhibit high density (2 × 1012 cm−2), small size (2–4nm) and good uniformity both in spatial distribution and morphology. The charging and long-term retention performances are explained by the Coulomb Blockade phenomena and the asymmetric electron tunnel barrier between the Ru NCs and the Si substrate, respectively.

Ge quantum dot infrared photo-detector

In our experiments, vertical aligned superlattices of multiple self-assembled Ge island layers separated by Si spacer layers on Si(100) substrates have been grown by ultra high vacuum chemical vapor deposition system (UHV/CVD). The photoluminescence of material was excited with 500nm laser and measured at 10 K, the PL peaks representing Ge islands and Si wetting layers were observed at 825 and 1010 mev respectively. Based on this material, samples of quantum dot infrared photo-detectors (QDIP), with p-i-n junctions, were fabricated. The responsivity of the detectors was measured with various semiconductor light-emitting diodes and semiconductor lasers. At room temperature and at -3V applied bias, for samples with 245 /spl times/ 245 /spl mu/m/sup 2/ large window and dark current I/sub d//spl sim/10/sup -9/A, the maximum photocurrent responsivity of 0.52 A/W at 774 nm was found, and 0.043mA/W at 1.31 /spl mu/m. Higher responsivities can be obtained with a waveguide geometry and optimization of the whole structure, such as thickness of layers and type of doping.

Manufacture of SiGe HMOSFET

The advances in the growth of pseudomorphic silicon-germanium epitaxial layers combined with the strong need for high-speed devices have led to increased interest in silicon-based heterojunction field-effect transistors. Here we present a kind of strained SiGe-channel P-MOSFET which can offer better performance compared to the Si device. When applying to the sample with W/L value of 14/7, a 30% improvement can be achieved in transconductance.

Spin Injection from Ferromagnetic Metal Directly into Non-Magnetic Semiconductor under Different Injection Currents

For ferromagnetic metal (FM)/semiconductor (SC) structure with ohmic contact, the effect of carrier polarization in the semiconductor combined with drift part of injection current on current polarization is investigated. Based on the general model we established here, spin injection efficiency under different injection current levels is calculated. Under a reasonable high injection current, current polarization in the semiconductor is actually much larger than that predicted by the conductivity mismatch model because the effect of carrier polarization is enhanced by the increasing drift current. An appreciable current polarization of 1% could be achieved for the FM/SC structure via ohmic contact, which means that efficient spin injection from FM into SC via ohmic contact is possible. The reported dependence of current polarization on temperature is verified quantitatively. To achieve even larger spin injection efficiency, a gradient doping semiconductor is suggested to enhance the drift current effect.

Formation of stacked ruthenium nanocrystals embedded in SiO2 for nonvolatile memory applications

Two methods are proposed to fabricate stacked ruthenium (Ru) nanocrystals (NCs): rapid thermal annealing (RTA) for the whole gate stacks, and RTA before each SiO2 layer deposition. The size and aerial density of Ru NCs are 2–4 nm and 3 × 1012 cm−2 for the former method, compared to 3–7 nm and 2 ×1012 cm−2 for the latter. Because of the higher surface trap density and more uniform electron tunneling path between upper and lower Ru NCs, a 5.2 V memory window and 1 V after a period of 10 years are observed in metal oxide semiconductor (MOS) capacitors fabricated by the former method, which are much better than 4.6 V and no window remaining after one year observed in the latter. The former method is compatible with conventional CMOS technology.

Dependences of spin polarization on the control parameters in the spin-polarized injection through the magnetic p-n junction

Effective spin-polarized injection from magnetic semiconductor (MS) to nonmagnetic semiconductor (NMS) has been highlighted in recent years. In this paper we study theoretically the dependence of nonequilibrium spin polarization (NESP) in NMS during spin-polarized injection through the magnetic p-n junction. Based on the theory in semiconductor physics, a model is established and the boundary conditions are determined in the case of no external spin-polarized injection and low bias. The control parameters that may influence the NESP in NMS are indicated by calculating the distribution of spin polarization. They are the doping concentrations, the equilibrium spin polarization in MS and the bias. The effective spin-polarized injection can be realized more easily by optimizing the above parameters.

Simulation study of new 3-terminal devices for high speed STT-RAM

To improve the performance of spin transfer torque random access memory (STT-RAM), especially writing speed, we propose three modified 3-terminal STT-RAM cells. A magnetic dynamic process in the new structures was investigated through micro-magnetic simulation. The best switching speed of the new structures is 120% faster than that of the rectangular 3-terminal device. The optimized 3-terminal device offers high speed while maintaining the high reliability of the 3-terminal structure.

Investigation of Composition in Nano-Scaled Self-Assembled SiGe Islands

A modified model is proposed to explain the influence of Si concentration on shape transition of self-assembled SiGe islands on Si substrates. The experimental results show that the critical sizes for shape transition from pyramids to domes (44, 50 and 60 nm) increase with the increasing Si concentration (0.032, 0.09 and 0.17) from sample A to C. Based on the proposed model, the quantitative relation between the Si concentration and the critical size is established. Then the composition exactly in nano-scaled self-assembled SiGe islands is calculated from the measured critical size. The result shows that the Si concentration deduced from Raman spectrum is much larger than the actual values. It is demonstrated that the quantitative relation we obtained can be used to investigate the composition in nano-scaled SiGe islands.

SiGe HV/CVD epitaxy growth on patterned Si substrate

This letter investigates the SiGe epitaxy growth on patterned Si substrate (patterned SiO/sub 2/ on Si substrate), and shows that the crystal quality of the SiGe/Si interface is excellent and that the SiGe epitaxial thin film on Si substrate in the patterned window is a single crystal.