Hong-Shick Min

An extended proof of the Ramo-Shockley theorem

Abstract An introduction of a new functional form of Greens theorem for inhomogeneous media has enabled us to show that the Ramo-Shockley theorem derived for inhomogeneous media with electrodes maintained at constant potentials is still valid even when the electrode potentials are time-varying. Our proof, which is based on this modified Greens theorem, is an extension of Ramos original proof and is different from the energy balance method which is the existing method of proof of the theorem for inhomogeneous media at constant electrode potentials. Our proof provides a basis for calculations of the instantaneous currents in semiconductor devices using particle simulations such as the Monte-Carlo method since it differentiates clearly the current induced in the electrodes due to the moving charges from the current caused by the time-varying potentials of the electrodes through capacitive couplings among the electrodes.

Electron mobility behavior in extremely thin SOI MOSFET's

Extremely thin-film SOI MOSFETs with silicon film thickness down to 8 nm have been fabricated without inducing serious source/drain series resistance by employing a gate recessed structure. The influence of extremely thin silicon film on the electron mobility has been experimentally studied. The results show an abrupt mobility decrease in the device with less than 10 nm silicon film thickness. The measured mobility versus effective field below 10 nm silicon film thickness shows that a different scattering mechanism is involved in carrier conduction in 10 nm t/sub si/ region. The reasons for the mobility decrease have been examined from a device simulation and measurements. >

Modeling the substrate effect in interconnect line characteristics of high-speed VLSI circuits

A new analytic model for interconnect characteristics is proposed. The model includes the frequency-dependent distribution of the current on the interconnect lines and the substrate as the current path. The validity of the proposed model has been checked by a comparison with the measurement data and the numerical simulation. Through this work, it is found that the substrate return path must be considered for the accurate prediction of the high-frequency characteristics of interconnects.

A time dependent hydrodynamic device simulator SNU-2D with new discretization scheme and algorithm

A two-dimensional device simulator SNU-2D based on the hydrodynamic model is developed for the simulation and analysis of submicron devices. The simulator has the capacity for both self-consistent steady-state and transient-state simulation. To obtain better convergence and numerical stability, we adopt an improved discretization scheme for the carrier energy flux equation and a new strategy for the transient simulation. In steady-state simulation the new discretization scheme shows a considerable improvement in convergence rate and numerical accuracy compared with the existing schemes. A transient simulation study is carried out on a deep submicron n-MOSFET used in the sense amplifier of SRAM cells to investigate the gate-switching characteristic. It is found that the behavior of carrier temperature is quasi-static during the switching time even for very fast switching speed, while the behavior of impact ionization under transient mode deviates from that under dc mode as the switching speed increases. >

Impact ionization modeling using simulation of high energy tail distributions

A new model for the impact ionization using the tail electron density is proposed. A new hydrodynamic model is used to compute the tail carrier quantities. The discretization method and numerical procedures are explained. The model parameters are extracted from the space-dependent Monte Carlo simulations. The simulated results for an n/sup +/-n/sup -/-n/sup +/ diode and a DILDD n-MOSFET are shown and give good agreement with Monte Carlo simulations and measurements, respectively.<<ETX>>

Channel length independent subthreshold characteristics in submicron MOSFETs

This work reports an anomalous subthreshold characteristic of the MOSFET for the first time. It is observed that the subthreshold characteristic does not change as the channel length decreases. The cause of channel length independent subthreshold characteristics is identified as the localized pileup of channel dopants near the source and drain ends of the channel. The low surface potential of this pileup region limits the subthreshold current of MOSFET. As a result, the ratio of on-current to off-current for this MOSFET increases as the channel length is reduced, which is an important parameter for low-voltage operation. It is found that a MOSFET with channel length independent subthreshold characteristic is more suitable for low-voltage operation.

Drain current enhancement due to velocity overshoot effects and its analytic modeling

The drain current enhancement due to the velocity overshoot effects is found to be due to the electron velocity enhancement at the source end. Based on this observation, a new analytic model is proposed and verified by two-dimensional (2-D) simulations and experiments. From the results of the verifications, we conclude that our model predicts the drain current enhancement due to the velocity overshoot effects reasonably well. The effects of the device parameters, such as gate oxide thickness and channel doping concentration, on the drain current enhancement ran be readily found in our model.

A unified theory of noise in nondegenerate semiconductors

Explicit forms of the Langevin noise sources due to both intraband and interband scattering are given for the Boltzmann transport equations with the relaxation‐time approximation in nondegenerate semiconductors. A generalized formula for the short‐circuited noise currents, which holds in both homogeneous and nonhomogeneous one‐dimensional nondegenerate semiconductors, is derived in a unified manner by solving the Langevin‐type Boltzmann transport equations. From this generalized noise formula the short‐circuited noise currents for thermal noise, generation‐recombination noise, and 1/f noise in a homogeneous nondegenerate semiconductor bar are calculated. It is shown that for homogeneous nondegenerate semiconductors, Nyquist’s theorem always holds both at thermal equilibrium and under an applied dc electric field with either intraband scattering or interband scattering dominant. Generation‐recombination noise is shown to be caused by the electrons or holes whose scattering mechanism is dominated by intraba...

Langevin noise sources for the Boltzmann transport equations with the relaxation‐time approximation in nondegenerate semiconductors

An analytic and useful form of the noise sources due to intraband scattering for the Boltzmann transport equations in the relaxation‐time approximation is obtained for nondegenerate semiconductors. It is shown that the derived noise source gives the Nyquist’s theorem.

A novel bipolar imaging device - BASIC (BAse stored imager in CMOS Process)

A new pixel structure named base stored imager in CMOS process (BASIC), is proposed and realized with a conventional 1.5 /spl mu/m CMOS process. The BASIC cell comprises three pMOSFETs and a new photosensor, which has the gate-body tied nMOSFET structure. The BASIC cell achieves high responsivity because the photosensor amplifies the photogenerated electron-hole pairs. Dynamic range is improved by using the reset of the base through the pMOSFET and correlated double sampling operation. The structure and operation principles of the BASIC cell are presented together with measurement results from the fabricated samples. It is shown that the BASIC cell can be scaled down for large arrays and it is adequate for low voltage operation.