Thermal noise in buried-channel MOSFET

A new model for the thermal noise in long buried-channel MOS transistors is presented. The model calculates the dependence of the transistor noise performance on both device fabrication parameters and the four terminal voltages. The noise calculations are based on the gradual channel approximation, using simple charge-voltage relations. Analytic models are obtained for the different regions of operation of the transistor. Noise measurements are presented and compared with results predicted by the model     

Impact of transport noise enhancement in scaled-down MOSFET

This paper describes a theoretical approach to understanding the impact of carrier-density-fluctuation-induced high-frequency transport noise in scaled-down MOSFETs. A theoretical expression is formulated on the basis of the charge-density conservation equation and current continuity condition. The relation between drain current noise and carrier-density fluctuation is also discussed. As scaling level is increased, the high-frequency component of normalized carrier-density fluctuation power is enhanced because the averaging effect of fluctuation power is suppressed. It is shown that the high-frequency component of drain current noise in a 0.1-μm-channel device is more significant than that in a 1-μm-channel device.     

EMI-induced failures in crystal oscillators

An electromagnetic interference (EMI) induced failure mode pertaining to crystal-based voltage-controlled oscillators (VCO) has been studied. The failure consists of a transition to a frequency of oscillation that differs from the crystal's fundamental resonant frequency, when the circuit is temporarily exposed to continuous or pulsed radio-frequency electromagnetic fields. The new state persists even after the EMI source is removed and leads to hang-up in digital systems. This mode transition has been observed experimentally. Its essential properties have been predicted theoretically and simulated numerically, using simplified oscillator models. The likelihood of observing such a failure in a noisy electromagnetic environment is assessed with respect to the radiated susceptibility levels given in MIL-STD-461B     

Investigation of MOSFET failure in soft-switching conditions

Thanks to an ad-hoc experimental test equipment, the reliability of MOSFET devices in soft-switching operations has been investigated aimed to discovering the role of the freewheeling phase in the device reliability reduction. Extensive tests at several temperatures, on-state currents, reverse current peaks, dc-voltages and gate timings have been done, showing that specific devices for soft-switching are needed to improve the overall converter reliability. Standard commercial MOSFETs are more prone to failures descending from huge power dissipation at the gate turn-off, related to preceding body diode usage.     

Influence of noise intensity on the spectrum of an oscillator

This paper investigates the influence of high-intensity noise on the correlation spectrum of a two-dimensional (2-D) nonlinear oscillator. An exact analytical solution for the correlation spectrum of this 2-D oscillator is provided. The analytical derivations are well suited for oscillators with white noise of any intensity, but computational constraints on the solution of the partial differential equation may make it impractical for cases where the number of state variables exceeds three. The spectral results predicted by our analytical method are verified by numerical simulations of the noisy oscillator in the time domain. We find that the peak of the oscillator spectrum shifts toward higher frequencies as the noise intensity is increased, as opposed to the fixed oscillation frequency predicted in the existing literature. This phenomenon does not appear to have been reported previously in the context of phase noise in oscillators.     

Investigation of MOSFET operation in bipolar mode

The work is concerned with the properties of conventional MOSFET in bipolar mode of operation. It is shown that the base current can provide useful information about interface trap density at the Si–SiO₂ interface. The new device characteristics are found promising for use in low-voltage low-power logic circuits.     

A physical thermal noise model for SOI MOSFET

The recent progress in SOI technology necessitates an accurate thermal noise model for wide-band SOI analog IC design. In this paper a physical-based thermal noise model is proposed for floating-body SOI MOSFET operated in strong inversion regime and verified by the experimental data. In the model, both the lattice temperature (unique to SOI due to the buried oxide) and the carrier temperature (significant for short-channel device in saturation region) are considered. The model agrees well with the experimental data     

Direct parameter-extraction method for MOSFET noise model from microwave noise figure measurement

A new method for the determination of the four noise parameters of the metal oxide semiconductor field effect transistors (MOSFETs) based on the noise figure measurement system without microwave tuner is presented. The noise parameters are determined based on a set of analytical expressions of noise parameters by fitting the measured noise figure of the active device. These expressions are derived from an accurate small signal and noise equivalent circuit model, which takes into account the substrate parasitics, pad capacitances, and series inductances. On-wafer experimental verification is presented and a comparison with tuner based method is given. Good agreement is obtained between simulated and measured results for 0.5 × 5 × 16 μm, 0.35 × 5 × 16 μm and 0.18 × 5 × 16 μm (gate length × number of gate fingers × unit gate width) MOSFETs.     

Comments on circuit models for MOSFET thermal noise

It is shown that some current and proposed SPICE models for MOS thermal noise are inconsistent, either when moving from one operating region to another or when changing model levels. A different model is shown to be consistent with theory in all regions and with all SPICE model levels. The reasons for the inconsistency are explored     

MOSFET thermal noise modeling for analog integrated circuits

The effects of device geometry, oxide thickness, and bias condition on the thermal noise of MOSFET's are investigated. The experimental results show that the conventional MOSFET thermal noise models do not accurately predict the thermal noise of MOSFET's. A model that is capable of predicting the thermal noise of both long and short channel devices in both the triode and saturation regions is presented. This model, which can be easily implemented into existing circuit simulators such as SPICE, has been verified by a wide variety of measurements     

A physics-based MOSFET noise model for circuit simulators

Discussed is a physics-based MOSFET noise model that can accurately predict the noise characteristics over the linear, saturation, and subthreshold operating regions but which is simple enough to be implemented in any general-purpose circuit simulator. Expressions for the flicker noise power are derived on the basis of a theory that incorporates both the oxide-trap-induced carrier number and correlated surface mobility fluctuation mechanisms. The model is applicable to long-channel, as well as submicron n- and p-channel MOSFETs fabricated by different technologies, and all the model parameters can be easily extracted from routine I-V and noise measurements     

Effect of hot-electron stress on low frequency MOSFET noise

Hot-electron reliability problems are of great importance in small geometry n-channel field-effect transistors. Accumulation of negative charge within the gate insulator and creation of interface states represent the two dominant degradation mechanisms. Since MOSFET noise is ascribed to Si-SiO2interface states, one might reasonably expect this noise to increase after hot-electron stress. We verify this expectation and show how the noise increase depends on gate voltage during stress. MOSFET noise is important for analog circuit performance and, hence, consideration of the long-term stability of noise, as well as threshold voltage and transconductance, should be included in analog circuit/process design.     

The quantization noise spectrum of a sinusoid in colored noise

The power density spectrum (PDS) of analog-to-digital (A/D) quantization noise is obtained for an input signal consisting of sinusoid and colored noise. While this type of quantization noise is often assumed to be uncorrelated or white, it may not be when the input signal occupies a relatively small number of quantization levels. Equations describing the PDS are derived and presented for combinations of deterministic and random A/D converter inputs     

Dependence of MOSFET noise parameters in n-channel MOSFETs on oxide thickness

The expression for the $\text{1}\text{f}$ noise resistance R_n of a MOSFET at low drain bias contains the factor I_d²/[g_m(V_g-V_T)]², which is unity in the elementary MOSFET theory but can be considerably larger than unity in practical units. The number fluctuation model characterizes R_n further by the parameter [N_T(E_f)]_eff/? and the mobility flucuation model introduces Hooge's parameter α. Measurements show that [N_T(E_f)]_eff/? varies as t^?2, α as t^?1 and the mobility μ varies as t, where t is the oxide thickness. The dependence of R_n upon T is chiefly determined by the t-dependence of the factor I_d²/[g_m(V_g-V_T)]². Since the drain noise spectrum S_Id(f) is practically independent of t, it is a very useful parameter for characterizing the noise. All data are now mutually consistent.     

Statistical BSIM model for MOSFET 1/f noise

A statistical model for MOSFET 1/f noise implemented as an extension to BSIM and integrated into a process design kit is presented. Excellent model to hardware correlation is shown on measured noise statistics from over 200 devices. The statistical model enables circuit designers to run Monte Carlo and corner noise simulations, and captures the device area and bias dependence of noise variance.     

Improved low frequency noise model for MOSFET operated in non-linear region

An improved LF noise model with correlated mobility fluctuations is proposed for MOSFET operated in non-linear region. This model well explains the decrease of the input gate voltage S_Vg with drain voltage, unlike the standard carrier number fluctuations model.     

Investigation of a multigigahertz MOSFET amplifier with an on-chipinductor fabricated on a SIMOX wafer

This paper describes a technology that can be used to integrate multigigahertz RF circuits into large-scale digital circuits. Spiral inductors and a MOSFET amplifier with an inductive load were fabricated on a SIMOX wafer in order to demonstrate the feasibility of SOI technology. With a 1-V supply voltage, peaking of the amplifier gain was observed, as expected from circuit simulations, at 1-4 GHz. These results show that RF circuits with inductors can be implemented on a SIMOX wafer by using the conventional digital CMOS LSI process