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A novel rectangular shape differential CMOS split-drain Hall Effect magnetic field-effect transistor (MAGFET) was designed and fabricated employing a CMOS 0.5 μm process. The detection and monitoring of single 2.8 μm diameter magnetic beads was successfully performed using this MAGFET design. Based on the device modeling, simulation and the signal to noise ratio analysis, it was found that the optimal sensitivity can be achieved when the MAGFET channel width to length ratio is equal to 1.3. Further, it is shown through that when the MAGFET is scaled down, its SNR performance can sustain its peak, while being more sensitive to the geometry variations.

A novel circular CMOS MAGFET (Magnetic Field Effect Transistor) design is introduced and a novel device geometry design methodology is proposed to optimize the magnetic particle detection sensitivity of such devices. In order to optimize the signal to noise ratio, it was determined that the geometry of the MAGFET is required to have specific ratios, where its sector angle θ and its inner and outer radii r1 and r2 are optimized when θ/ln(r2/r1) = 1.3 . Compared to the more traditional rectangular MAGFET, the circular MAGFET has compatible SNR peak performance with rectangular MAGET. However, when the size of the MAGFET is scaled down in order to detect smaller magnetic particles, the proposed circular MAGFET has more robust SNR performance, design flexibility and tolerance to processing variations.

A new model to semiconductor device electronic noise is presented in the framework of semiclassical transport theory. The salient feature of this model is that it connects the current noise characteristics directly to the physics of scattering of the semiclassical transport theory and makes no additional assumption regarding the nature of noise. Employing this approach, this work investigates the spatial origin of the current noise across two semiconductor structures. In this approach the terminal current noise is directly related to carrier scattering inside the device, which is accounted for in the Boltzmann transport equation (BTE), without the need to add Langevin noise terms to the calculations. Accordingly, it utilizes the well-established spherical harmonics expansion (SHE) technique to solve the BTE, and it combines analytical and numerical methods, in contrast with the Monte Carlo (MC) approach that employs ensemble averages of randomly generated events. The model leads to the solution of a time-dependent transient solution of the BTE with special initial and Ohmic boundary conditions that is solved in the frequency domain to directly compute the terminal current noise spectral density. It is also shown that with this approach the Nyquist theorem under thermal equilibrium conditions is recovered.

A special measurement system is developed to measure the combined noise and reliability of a three-axis micro-accelerometer. Three parametric tests are provided: gravitational, thermal and acoustical. The measurements were performed on both the in-plane and the out-of-plane axes. The temperature-dependence and acceleration-dependence of the noise was found, in agreement and contrast to the theories. The device is found to be very reliable when subjected to individual tests, but exhibits slight deviations during the combined tests.

Noise measurements of micro-accelerometers were performed using a special measurement system. A common spectral behavior of noise is found, with 1/f noise dominating at low frequencies and white thermal noise being the limiting factor at higher frequencies. Unexpected resonances are also observed in the commercial devices. Most importantly, an acceleration dependent of the noise is found in analog devices and freescale accelerometers, in contrast to prevailing theory.

The operation of a nonlinear binary detector with hysteresis is investigated. Prior models developed for continuous time inputs are extended for the computationally more efficient discrete-time inputs. The input to the rectangular hysteresis detector is modeled to be a binary signal in the presence of additive independent identically distributed noise. The rectangular hysteresis loop models one of a number of rate independent repeaters in an optical communication link. The link is terminated by a binary discriminator that is tuned to a particular bit duration. The study shows that key calculations to compute the bit error probability can be performed by employing the formalism of discrete Markov chains.

Processes of origin and relaxation of fluctuations of the conduction electrons’ distribution function in space-homogenous and non-degenerate thermal equilibrium semiconductors are discussed. It is shown that in low-frequency region the Fourier-component of the long-wavelength electrons and phonons distribution function's fluctuating component is directly proportional to ω - 1 / 2 . It is shown that electron energy and/or quasi-momentum fluctuations may contain the Schonfeld pulse and that the Schonfeld model can directly be incorporated into physical model describing 1 / f -type noise formation in semiconductors. It is suggested that the concept of “Thermal Equilibrium Semiconductor” can be reconsidered when one studies fluctuation phenomena, in particular 1 / f -noise. It is demonstrated that the electron–phonon system always stays in non-equilibrium condition from point of view of the fluctuation theory.

Microelectromechanical systems (MEMS) are devices that have static or movable components with dimensions on the scale of a micrometer. One particular device that is widely used commercially is the MEMS accelerometer. Such accelerometers typically contain some movable micro beams that measure acceleration in one or two orthogonal directions. Major markets for MEMS accelerometers are automobile airbag triggers, earthquake detection circuits and health care. MEMS accelerometers have advantages over conventional accelerometers because they are smaller, lighter and cheaper. Since MEMS accelerometers are used in many systems, the noise characteristics of these devices are very important. The noise characteristics will influence the performance of the accelerometers especially when operating at lower g conditions. In this work, we report on the noise characteristics and special measurement techniques for Analog Devices ADXL202, ADXL 105 and ADXL 190 accelerometers.

A nonlinear filter with hysteresis is presented to detect binary signals. It is shown that key calculations for the bit error rate are reduced to the “exit problem” of stochastic differential equation theory. Employing this formalism, closed form expressions are derived in the transform domain for the probability density function of the filter output in the presence of additive white Gaussian noise. By taking inverse transformations, such expressions can be used to compute several performance measures of binary detectors with hysteresis nonlinearity.

Preisach-based aftereffect models are employed to define the ground state of a magnetic system. Four different types of processes due to thermal perturbations, AC demagnetization, Curie point demagnetization and DC demagnetization are reviewed and compared with each other. By modeling the time evolution of the magnetization and magnetic field on the Preisach plane, it is shown that the asymptotic state of the system due to thermal perturbations is the true magnetic ground state.

The sigmoidal decay of the magnetization in log time, which is geometrically similar to the major loop, starts at the major loop and decays to the anhysteretic magnetization for a given holding field. The linear displacement of these curves after normalization with holding field can be used to compute the fluctuation field. This paper discusses the errors in computing this field.

The article reviews a novel approach to the modeling of after-effect phenomena in hysteretic systems. The after-effect model is based on Preisach-type models driven by stochastic inputs. Random thermal perturbations which result in the gradual loss of memory in hysteretic systems are modeled by discrete and continuous-time stochastic processes. The important properties of the after-effect model are summarized and compared with the traditional thermal activation-type models and with some known experimental facts.

This review article summarizes our work during the past five years on a new approach to the modeling of aftereffect phenomena in hysteretic systems, This approach is based on Preisach type models driven by stochastic inputs. Both the classical and nonlinear Preisach models are employed in this approach. Thermal perturbations which result in the gradual loss of memory in hysteretic systems are modeled by discrete and continuous time stochastic inputs. The important properties of the aftereffect model are highlighted and compared with the traditional thermal activation type models and with some known experimental facts.

Our implementation of a fixed-point iteration technique for the three-dimensional (3D) steady-state simulation of MOSFET devices is presented. The simulation program is employed to investigate narrow channel effects on the device current-voltage characteristics. Particularly, the effects of impact ionization and the effects of variations in channel width and the field oxide bird's beak angle are evaluated. The degree to which various field oxide configurations isolate the device from the gate contact over the oxide transition region is determined by comparing the current-voltage characteristics with those of an idealized device with perfect isolation. Perfect isolation is simulated by setting the normal component of the electric field to zero at the semiconductor-field oxide interface. Simulation results show that the 3D computations are essential to account for rapidly varying charge densities and generation rates near the channel edge. Moreover, it is observed that the isolation effects of field oxides increase for larger bird's beak angles.

This paper presents a new approach to model hysteresis and aftereffect phenomena. A dynamic approximation of rectangular hysteresis loops is employed that leads to the representation of the input-output relationship as a first-order dynamical system driven by white noise. Closed-form expressions are derived for the output of rectangular loops in terms of convolution-type integrals. The formalism allows one to circumvent some of the mathematical challenges associated with history-dependent switching of rectangular hysteresis loops driven by stochastic processes.

We present a numerical technique which employs a local-in-time initial guess for the transient simulation of SOI MOSFETs. Specifically, the goal of this work is to compute the transient drain current which exhibits overshoot. A critical factor in such computations is the choice of the initial guess at each time point after the gate ramp. Our numerical simulations have shown that the use of the previous time point solution as an initial guess in the Gummel iterations fails to predict the decay in the drain current from its maximum overshoot value. This difficulty is circumvented when the steady-state solution is used as a local-in-time initial guess. We use the diagonally implicit Runge-Kutta method for the time domain discretization. A fixed-point iteration technique is employed for the space domain iterations. To demonstrate the usefulness of the local-in-time method, numerical results of the transient drain current for various device parameters, such as the silicon film doping, silicon film thickness and back-gate bias are presented.

Preisach models driven by stochastic inputs are employed to model magnetic aftereffect in the presence of demagnetizing fields. As a result of thermal relaxation, the magnetization and, consequently, the demagnetizing field vary in time. The new model generalizes earlier work and self-consistently accounts for the effect of time varying demagnetizing fields on the relaxation process. Three practical numerical techniques are proposed to compute the time variation in the magnetic field and the state of the Preisach plane.

Simulation results are presented for a MOSFET with position- and energy- (potential-) dependent interface trap distributions that may be typical for devices subjected to interface-trap-producing processes such as hot-electron degradation. The interface-trap distribution is modeled as a Gaussian peak at a given position along the channel, and the energy dependence is derived from C-V measurements from an MOS capacitor exposed to ionizing radiation. A novel fixed-point technique is used to solve the two-dimensional boundary-value problem. The technique is shown to be globally convergent for arbitrary distributions of interface traps. A comparison of the convergence properties of the Newton and fixed-point methods is presented, and it is shown that for some important cases the Newton technique fails to converge while the fixed-point technique converges with a geometric convergence rate. >

Recently, several aftereffect models were proposed in which Preisach type hysteresis transducers are driven by stochastic inputs. Such inputs represent random thermal perturbations which are the source of the aftereffect phenomenon. According to these models, aftereffect is completely characterized by the magnetization history, the Preisach function and noise parameters. In this article, we present an identification of model parameters in which temperature-dependence is incorporated into the aftereffect model. The temperature variation of the noise parameters are investigated in order to predict the aftereffect decay coefficient. Comparison of numerical results with experimental ones observed in metal particle tape (MPT) magnetic recording media show a good agreement. As a result, based on the magnetization history, the Preisach function and noise parameters, it is shown that the model can be used to predict aftereffect characteristics of magnetic recording media of arbitrary magnetization history and temperature.

Previously, several aftereffect models were proposed in which Preisach type hysteresis transducers are driven by stochastic inputs. Such inputs model random thermal perturbations which are the source of aftereffect phenomena. In this article, we compare experimental and numerical simulation results for the first time in order to verify the proposed models, and present an identification procedure to determine aftereffect model parameters. Numerical simulations of the aftereffect model show the well known log t-type decay in magnetization whose rate reaches a maximum near the coercive field. Comparison of these with experimental results from /spl gamma/-Fe/sub 2/O/sub 3/ recording media show excellent agreement. Based on this comparison, we propose a practical procedure to identify the stochastic parameters of the aftereffect model.

The switching characteristics of ultra-thin SOI CMOS inverters with hot-carrier-induced degradations are examined by using device simulations. The simulator employs a robust fixed-point iteration method to avoid conventional matrix solutions. Potential-dependent interface traps and oxide trapped charges are used to model the degradations. The effects of front and back channel degradations in an nMOS device of a CMOS inverter are investigated in steady-state and transient regimes. The nonlinear variation of interface charges cannot be simulated by using a single nMOS device alone since the transition of the inverter is also determined by the pMOS transistor. It is found that the stagnant holes generated by impact ionization have a much greater effect on the rate of the pull-down transient than that of interface charges.

Previously, it has been shown that Preisach type models driven by stochastic inputs can be employed to model aftereffect. In this model, the machinery of the "exit problem" is instrumental in computing the time evolutions of the expected value and the distributions of switching times. Here, for the first time, we present numerical simulation results of the aforementioned viscosity models and demonstrate that these models can be employed to compute switching times and time evolutions of the expected value of magnetization.

In a previous work, it has been suggested to use the Preisach model driven by stochastic inputs as a model for aftereffect. Here, we further extend this approach by employing the more accurate nonlinear input dependent Preisach model. The time evolution of the expected value of the output (magnetization) is derived in terms of the stochastic description of the input. It is shown that the mathematical machinery of the "exit problem" is instrumental for calculations of time evolutions of the expected value of the output of the nonlinear input dependent Preisach model. >

The authors had previously proposed the use of the classical Preisach model driven by stochastic inputs as a model of viscosity in hysteretic systems. Here, this approach is extended by utilizing the nonlinear (input dependent) Preisach model of hysteresis. This model is more general than the classical Preisach model, but its treatment encounters some technical difficulties. As a useful by-product, the authors investigate the viscosity phenomenon in Stoner-Wohlfarth-type particles. >