C. Hu

Bio: C. Hu is an academic researcher from University of California, Berkeley. The author has contributed to research in topics: Field-effect transistor & MOSFET. The author has an hindex of 27, co-authored 48 publications receiving 3102 citations.

Threshold voltage model for deep-submicrometer MOSFETs

Abstract: The threshold voltage, V/sub th/, of lightly doped drain (LDD) and non-LDD MOSFETs with effective channel lengths down to the deep-submicrometer range has been investigated. Experimental data show that in the very-short-channel-length range, the previously reported exponential dependence on channel length and the linear dependence on drain voltage no longer hold true. A simple quasi-two-dimensional model is used, taking into account the effects of gate oxide thickness, source/drain junction depth, and channel doping, to describe the accelerated V/sub th/ on channel length due to their lower drain-substrate junction built-in potentials. LDD devices also show less V/sub th/ dependence on drain voltage because the LDD region reduces the effective drain voltage. Based on consideration of the short-channel effects, the minimum acceptable length is determined. >

A true single-transistor oxide-nitride-oxide EEPROM device

Abstract: A novel single-transistor EEPROM device using single-polysilicon technology is described. This memory is programmed by channel hot-electron injection and the charges are stored in the oxide-nitride-oxide (ONO) gate dielectric. Erasing is accomplished in milliseconds by applying a positive voltage to the drain plus an optional negative voltage to the gate causing electron tunneling and/or hot-hole injection due to the deep-depletion-mode drain breakdown. Since the injection and storage of electrons and holes are confined to a short region near the drain, the part of the channel near the source maintains the original positive threshold voltage even after repeated erase operation. Therefore a select transistor, separate or integral, is not needed. Because oxide layers with a thickness larger than 60 A are used, this device has much better data retention characteristics than conventional MNOS memory cells. This device has been successfully tested for WRITE/ERASE endurance to 10000 cycles.

Subbreakdown drain leakage current in MOSFET

Abstract: Significant drain leakage current can be detected at drain voltages much lower than the breakdown voltage. This subbreakdown leakage can dominate the drain leakage current at zero V G in thin-oxide MOSFET's. The mechanism is shown to be band-to-band tunneling in Si in the drain/gate overlap region. In order to limit the leakage current to 0.1 pA/µm, the oxide field in the gate-to-drain overlap region must be limited to 2.2 MV/cm. This may set another constraint for oxide thickness or power supply voltage.

Alpha-particle-induced field and enhanced collection of carriers

Abstract: A simple physical model explains all the characteristics of the newly discovered funnelling phenomenon. An alpha strike results in significant field in the quasi-neutral regions to a depth that is equal to 1 + µ _{n} /µ _{p} times the depletion region width of an n+/p junction. This and the predicted current waveform agree with experiments and simulation results. The model also predicts the effects of the angle of alpha incidence, and that p+/n junctions should exhibit weaker funnelling phenomenon.

A capacitorless double-gate DRAM cell

Abstract: A capacitorless double-gate DRAM (DG-DRAM) cell is proposed in this study. Its dual gates and thin body reduce off state leakage and. disturb problems. Dopant fluctuations, which can be particularly important in high-density arrays, are avoided by using a thin, lightly doped body. The cell's large body coefficient ((dV/sub T/)/(dV/sub BD/) transforms small gains of body potential into increased drain current. MEDICI simulations for 85/spl deg/C show that a DG-DRAM cell may sustain a measurable change in drain current several hundred milliseconds after programming. These characteristics suggest that a thin body, double-gate cell is an interesting candidate for high density DRAM technologies.

Fundamentals of Modern VLSI Devices

Abstract: Learn the basic properties and designs of modern VLSI devices, as well as the factors affecting performance, with this thoroughly updated second edition. The first edition has been widely adopted as a standard textbook in microelectronics in many major US universities and worldwide. The internationally-renowned authors highlight the intricate interdependencies and subtle tradeoffs between various practically important device parameters, and also provide an in-depth discussion of device scaling and scaling limits of CMOS and bipolar devices. Equations and parameters provided are checked continuously against the reality of silicon data, making the book equally useful in practical transistor design and in the classroom. Every chapter has been updated to include the latest developments, such as MOSFET scale length theory, high-field transport model, and SiGe-base bipolar devices.

Device scaling limits of Si MOSFETs and their application dependencies

Abstract: This paper presents the current state of understanding of the factors that limit the continued scaling of Si complementary metal-oxide-semiconductor (CMOS) technology and provides an analysis of the ways in which application-related considerations enter into the determination of these limits. The physical origins of these limits are primarily in the tunneling currents, which leak through the various barriers in a MOS field-effect transistor (MOSFET) when it becomes very small, and in the thermally generated subthreshold currents. The dependence of these leakages on MOSFET geometry and structure is discussed along with design criteria for minimizing short-channel effects and other issues related to scaling. Scaling limits due to these leakage currents arise from application constraints related to power consumption and circuit functionality. We describe how these constraints work out for some of the most important application classes: dynamic random access memory (DRAM), static random access memory (SRAM), low-power portable devices, and moderate and high-performance CMOS logic. As a summary, we provide a table of our estimates of the scaling limits for various applications and device types. The end result is that there is no single end point for scaling, but that instead there are many end points, each optimally adapted to its particular applications.

Two bit non-volatile electrically erasable and programmable semiconductor memory cell utilizing asymmetrical charge trapping

Abstract: An electrically erasable programmable read only memory (EEPROM) having a non conducting charge trapping dielectric, such as silicon nitride, sandwiched between two silicon dioxide layers acting as electrical insulators is disclosed. The invention includes a method of programming, reading and erasing the EEPROM device. The non conducting dielectric layer functions as an electrical charge trapping medium. A conducting gate layer is placed over the upper silicon dioxide layer. The memory device is programmed in the conventional manner, using hot electron programming, by applying programming voltages to the gate and the drain while the source is grounded. Hot electrons are accelerated sufficiently to be injected into the region of the trapping dielectric layer near the drain. The device, however, is read in the opposite direction from which it was written, meaning voltages are applied to the gate and the source while the drain is grounded. Application of relatively low gate voltages combined with reading in the reverse direction greatly reduces the potential across the trapped charge region. This permits much shorter programming times by amplifying the effect of the charge trapped in the localized trapping region. In addition, the memory cell can be erased by applying suitable erase voltages to the gate and the drain so as to cause electrons to be removed from the charge trapping region of the nitride layer. Similar to programming, a narrower charge trapping region enables much faster erase cycles.

NROM: A novel localized trapping, 2-bit nonvolatile memory cell

Abstract: This paper presents a novel flash memory cell based on localized charge trapping in a dielectric layer and on a new read operation. It is based on the storage of a nominal /spl sim/400 electrons above a n/sup +//p junction. Programming is performed by channel hot electron injection and erase by tunneling enhanced hot hole injection. The new read methodology is very sensitive to the location of trapped charge above the source. This single device cell has a two physical bit storage capability. The cell shows improved erase performances, no over erase and erratic bit issues, very good retention at 250/spl deg/C, and endurance up to 1M cycles. Only four masks are added to a standard CMOS process to implement a virtual ground array. In a typical 0.35 /spl mu/m process, the area of a bit is 0.315 /spl mu/m/sup 2/ and 0.188 /spl mu/m/sup 2/ in 0.25 /spl mu/m technology. All these features and the small cell size compared to any other flash cell make this device a very attractive solution for all NVM applications.

A 1.5-V, 10-bit, 14.3-MS/s CMOS pipeline analog-to-digital converter

Abstract: A 1.5-V, 10-bit, 14.3-MS/s pipeline analog-to-digital converter was implemented in a 0.6 /spl mu/m CMOS technology. Emphasis was placed on observing device reliability constraints at low voltage. MOS switches were implemented without low-threshold devices by using a bootstrapping technique that does not subject the devices to large terminal voltages. The converter achieved a peak signal-to-noise-and-distortion ratio of 58.5 dB, maximum differential nonlinearity of 11.5 least significant bit (LSB), maximum integral nonlinearity of 0.7 LSB, and a power consumption of 36 mW.