Mishel Matloubian

Single-transistor latch in SOI MOSFETs

A single-transistor latch phenomenon observed in silicon-on-insulator (SOI) MOSFETs is reported. This latch effect, which occurs at high drain biases, is an extreme case of floating-body effects which are present in SOI MOSFETs. The floating body results in positive feedback between the impact ionization current, body-to-source diode forward bias, and transistor currents. At large drain voltages, this positive feedback can maintain a high-drain-to-source current even when the MOS gate is biased well below its threshold voltage.<<ETX>>

Anomalous subthreshold current&#8212;Voltage characteristics of n-channel SOI MOSFET's

The abnormally high slopes of the subthreshold current-voltage characteristics exhibited by n-channel silicon-on-insulator (SOI) MOSFETs are experimentally related to defect density (off-state leakage current) as well as drain voltage and channel length, and a theoretical physical description of the measured relations is presented and supported. The anomalous subthreshold behavior is attributed analytically to the (floating) body effect due to charging (biasing) by impact ionization at the drain.

On the high-frequency characteristics of substrate resistance in RF MOSFETs

The high-frequency (HF) behavior of substrate components in MOSFETs is studied at different bias conditions for a 0.35 /spl mu/m BICMOS technology in the frequency range up to 10 GHz. It was found that the observed strong bias dependence of the real part of admittance y/sub 22/, Re{y/sub 22/}, is mainly contributed by the channel conductance. A very weak bias dependence of substrate resistance was found after deembedding the measured y/sub 22/ to remove the influence of channel resistance R/sub ds/ and gate-to-drain capacitance C/sub gd/. The results are key to the understanding and modeling of the HF behavior of MOSFET substrate components for RF IC design.

A broad-band lumped element analytic model incorporating skin effect and substrate loss for inductors and inductor like components for silicon technology performance assessment and RFIC design

We present a broad-band lumped element planar inductor model that is suitable for RFIC design in silicon technologies. We provide extensions of the modeling methodology to similar components such as differential inductors, baluns, and solenoid inductors. The analytic computation of the physics-based model components, incorporating both metal skin effect and substrate loss, is described. The model is validated using measured data from over 200 inductors made with five different silicon back-end process technologies. The physics-based implementation of the model allows its use for determining the optimum process technology characteristics for specific radio frequency integrated circuit (RFIC) designs. The analytical based implementation with lumped elements enables effective integration into a robust CAD system for efficient design of RFIC circuits.

Modeling of the subthreshold characteristics of SOI MOSFETs with floating body

n-channel SOI MOSFETs with floating bodies show a threshold voltage shift and an improvement in subthreshold slope at high drain biases. The magnitude of this effect depends on the device parameters and the starting SOI substrate. A simple device model is presented that explains the observed characteristics to be due to MOS back-bias effects resulting from the positively charged floating body. The improvement in the subthreshold slope is the outcome of positive feedback between the body potential and the transistor channel current. >

Parameter extraction of accurate and scaleable substrate resistance components in RF MOSFETs

Parameter extraction of the substrate resistance, which becomes important in radio frequency (RF) and mixed signal integrated circuit (IC) design, is discussed based on a simple substrate network of lumped components. By using the measured HF s-parameter data from a set of devices with different geometries, the scaleable parameters for substrate resistances components can be obtained. The simple substrate model with extracted scaleable parameters is accurate for devices with different widths and fingers in a frequency range up to 10 GHz.

Total Dose Characterizations of CMOS Devices in Oxygen Implanted Silicon-on-Insulator

The total dose characteristics of CMOS devices fabricated in oxygen implanted buried oxide silicon-on-insulator (SOI) substrates with different post-implant annealing processes are studied. The threshold voltage shift, subthreshold slope degradation and mobility degradation of front channel SOI/CMOS devices are measured to be the same as those of bulk devices processed identically. Negative substrate bias lowers the threshold voltage shift of back channel SOI transistors, while not affecting the front channel characteristics. Under present processing conditions, the radiation characteristics of front channel devices are independent of the postoxygen-implant annealing temperature. Oxygen precipitates at the silicon/buried oxide interface enhance interface state generation of the back channel devices during irradiation.

Measurement and modeling of the sidewall threshold voltage of mesa-isolated SOI MOSFETs

Five-terminal silicon-on-insulator (SOI) MOSFETs have been characterized to determine the threshold voltage at the front, back, and sidewall as a function of the body bias. The threshold voltage shift with the body bias at the front and back interfaces can be explained by the standard bulk body effect equation. However, the threshold voltage shift at the sidewall is smaller than predicted by this equation and saturates at large body biases. This anomalous behavior is explained by two-dimensional charge sharing between the sidewall and the front and back interfaces. An analytical model that accounts for this charge sharing by a simple trapezoidal approximation of the depletion regions and correctly predicts the sidewall threshold voltage shift and its saturation is discussed. The model makes it possible to measure the sidewall threshold even when it is larger than the front threshold voltage. >

Rapid-Thermal Nitridation of SiO2 for Radiation-Hardened MOS Gate Dielectrics

Nitridation of thin SiO2 layers has been achieved by a rapid thermal process in the presence of ammonia. The pre-and post-radiation performances of transistors with nitridated gate insulators have been presented. Nitridation causes a lowering of threshold voltage and channel mobility. Total dose testing indicates that nitridated gate oxides, under certain conditions, produce lower threshold voltage shift as well as less interface state generation than control (oxide) samples.

Frequency-dependent resistive and capacitive components in RF MOSFETs

It is found from measured high frequency (HF) S-parameter data that the extracted effective gate sheet resistance (R/sub gsh/), effective gate unit-area capacitance (C/sub gg, unit/), and transconductance (G/sub m/) in radio-frequency (RF) MOSFETs show strong frequency dependency when the device operates at frequencies higher than some critical frequency. As frequency increases, R/sub gsh/ increases but C/sub gg, unit/ and G/sub m/ decrease. This behavior is different from what we have observed at low or medium frequencies, at which these components are constant over a frequency range. This phenomenon has been observed in MOSFETs with L/sub f/ longer than 0.35 /spl mu/m at frequencies higher than 1 GHz, and becomes more serious as L/sub f/ becomes longer and the frequency higher. This behavior can be explained by a MOSFET model considering the Non-Quasi-Static (NQS) effect. Simulation results show that an RF model based on BSIM3v3 with the NQS effect describes well the behaviors of both real and imaginary parts of Y/sub 21/ of the device with strong NQS effect even though its fitting to Y/sub 11/ needs to be improved further.