Amitabh Chatterjee

High-speed light Modulation in avalanche breakdown mode for Si diodes

The light emission process from a p-n junction in the forward-bias region is slow to respond to modulation signals due to the indirect band structure of silicon. Experimental results for a reverse-bias region showing light modulation in the range of tens of gigahertz are observed for the first time. For such a light emitter, the limiting speed of light modulation is shown to be determined by the transit time of the minority carriers across the junction during the filament formation of breakdown currents, which has been demonstrated by simulation of the propagation of a shockwave-like pattern in the breakdown field.

All Si-based optical interconnect for interchip signal transmission

Barriers to the commercial implementation of optical interconnects between integrated circuits (ICs) center around the fabrication of optical elements on wafers through conventional Si processes. Most other approaches for optical interconnects use direct bandgap emitters that require drastic changes in conventional fabrication processes. In this work, we demonstrate the ability to transmit electrical signals using Si-based components, i.e., the light was generated by biasing a p-n junction at avalanche breakdown voltage, light was coupled through a fiber cable made of SiO/sub 2/, and detected by an Si-based avalanche photodiode. Results presented demonstrate the switching behavior of the light emitter, transmission of the signal across the fiber, and measurement of the signal limited by the bandwidth of the receiver amplifier.

Accelerated stressing and degradation mechanisms for Si-based photoemitters

A silicon p-n junction biased in avalanche breakdown mode emits visible light. Such a diode offers the potential for very large scale integration (VLSI)-compatible light emitters for on/off chip signal transmission and contactless functional testing of wafers. The reliability of such emitters must be evaluated before widespread use is possible. Si light emitters were stressed with ac excitation, dc excitation, and increased temperature to accelerate the aging. The results clearly show that the effects of ac and temperature stressing are negligible on light emission. DC stressing results in light coalescence for low values of current (less than 25 mA) with total light emission coming out of the junction remaining constant. However, dc stressing with large current values (larger than 40 mA) does not show light coalescence. The light coalescence phenomenon can be reversed when emitters are subjected to higher levels of currents. The difference in light coalescence behavior for large and small values of dc excitation and the reversibility of the phenomenon is consistent with the hydrogen migration model.

An Insight into the High Current ESD Behavior of Drain Extended NMOS (DENMOS) Devices in Nanometer Scale CMOS Technologies

Second breakdown phenomenon (It2) in drain extended NMOS (DENMOS) which is associated with complex triggering of the parasitic BJT is relatively less understood. We present experiments and models to understand the physics of snapback in DENMOS in nanometer scale technologies. Avalanche injection phenomenon at the drain contact has been analyzed for a 90 nm DENMOS transistor under high current stressing

An Insight Into the ESD Behavior of the Nanometer-Scale Drain-Extended NMOS Device—Part I: Turn-On Behavior of the Parasitic Bipolar

A second-breakdown phenomenon (It2) in a drain-extended n-type metal-oxide-semiconductor (DENMOS) is associated with complex triggering of a parasitic bipolar transistor. Full comprehension of the problem requires 3-D modeling; however, there is even deficiency in the understanding of the phenomenon occurring in the 2-D cross-sectional plane. We present experiments and models to understand the physics of bipolar turn-on and its impact on the onset of space-charge modulation in a DENMOS device. We present a detailed analysis of the current paths involved during the bipolar turn-on. We show that a strong snapback is triggered due to coupling of the parasitic bipolar turn-on in a deeper region of the p-body and avalanche injection at the drain junction. Furthermore, we show that the ballast resistor formed in the drain region due to current crowding of electrons under high-current conditions can be modeled through a simplified 1-D analysis of the n+/n- resistive structure.

Studies of charge carrier trapping and recombination processes in Si∕SiO2∕MgO structures using second-harmonic generation

Effects of MgO deposition on Si∕SiO2 system and charge carrier trapping and recombination in Si∕SiO2∕MgO structures are studied using second-harmonic generation (SHG). An ultrafast 800nm laser was used both for multi-photon induced electron injection through the SiO2 into a potential well in the MgO, and for monitoring the time-dependent SHG signal, which is sensitive to the electric field at the Si∕SiO2 interface. Our results indicate that the MgO deposition introduces new trap states, and electrons trapped in the MgO transport more readily through the SiO2 than those in traps on the surface of SiO2. We attribute this to differences in trap energy levels and/or differences in process damage-induced defect densities in the SiO2.

New physical insight and modeling of second breakdown (It/sub 2/) phenomenon in advanced esd protection devices

Second breakdown phenomenon in advanced NMOS ESD protection devices has remained an enigma due to the complex electrical and thermal effects that are responsible for its triggering. For the first time, we present a critical study of the high current phenomenon in ultra short-time scale to understand the physics of instability in protection devices around the second breakdown region. It is demonstrated that for advanced protection devices, carrier heating in the high field drain region causes a fall in the saturation drift velocity, which increases the transit time of carriers through the depletion region. This in turn, causes greater impact ionization due to higher accumulation of avalanche-generated carriers; leading to the formation of a propagating ionizing wave front, which culminates in a regenerative avalanche injection induced second breakdown failure

A Microscopic Understanding of Nanometer Scale DENMOS Failure Mechanism under ESD Conditions

We present for the first time, analysis of irreversible snapback caused due to the regenerative n-p-n turn-on in a DENMOS through a critical understanding of thermal runaway under ESD conditions. The estimated It2 value from transient simulations has been correlated with the quasi-steady TLP data. A new regenerative bipolar turn-on induced failure model has been proposed and corroborated with experimental observations and failure analysis. We have also investigated the current crowding mechanism to understand the improvement in It2 value under gate and substrate biasing.

Mechanisms leading to erratic snapback behavior in bipolar junction transistors with base emitter shorted

This paper discusses two different modes of breakdown in the reverse-biased I–V characteristics observed generically in bipolar junction transistors (BJTs) with the base emitter shorted, showing an erratic behavior, in the presence of large displacement currents. Experimental observations related to reverse-biased collector junctions of BJTs, that exhibit two different states of breakdown when a fast voltage ramp is applied are presented. Numerical simulations of the transient behavior of avalanche injection in p∕n−∕n+ structures show that two very close breakdown states coexist. The mechanisms leading to the erratic behavior of the second breakdown are discussed. The jittery nature of the breakdown is attributed to the delay associated with the buildup of the electric field across the n−∕n+ junction.

Robust high current ESD performance of nano-meter scale DeNMOS by source ballasting

“Strong Snapback” in DeNMOS transistors leads to weak ESD performance which is often represented by low It2 and strong die to die dependence. We report here the first experimental evidence that this can be controlled with introduction of source-resistance Rs. A new microscopic model has been analyzed to understand the physics of strong snapback and explain the experimental observations. Impact of current crowding phenomenon and role of adding a resistor across the source and ground has been broadly addressed in this paper. Also the current crowding phenomenon has been macroscopically modeled and a circuit model has been established.