Bert Vermeire

Mechanisms of Enhanced Radiation-Induced Degradation Due to Excess Molecular Hydrogen in Bipolar Oxides

Bipolar junction test structures packaged in hermetically sealed packages with excess molecular hydrogen (H2) showed enhanced degradation after radiation exposure. Using chemical kinetics, we propose a model that quantitatively establishes the relationship between excess H2 and radiation-induced interface trap formation. Using environments with different molecular hydrogen concentrations, radiation experiments were performed and the experimental data showed excellent agreement with the proposed model. The results, both experimentally and theoretically, showed increased radiation induced degradation with H2 concentration, and device degradation saturate at both high and low ends of H2 concentrations.

Band-to-Band Tunneling (BBT) Induced Leakage Current Enhancement in Irradiated Fully Depleted SOI Devices

We propose a model, validated with simulations, describing how band-to-band tunneling (BBT) affects the leakage current degradation in some irradiated fully-depleted SOI devices. It is demonstrated that the drain current dependence on total ionizing dose at negative gate bias can result from the combination of BBT and charge buildup in the BOX, including the transition to the high current state. The role of impact ionization is examined.

A Comparative Electrochemical Study of Copper Deposition onto Silicon from Dilute and Buffered Hydrofluoric Acids

An electrochemical direct current polarization method was used to investigate characteristics of copper deposition onto silicon from dilute and buffered hydrofluoric acid solutions. The corrosion current density and corrosion potential of silicon were not very sensitive to the Cu 2+ concentration, up to 1000 parts per billion, in buffered hydrofluoric acid. However, the extent of copper deposition, as measured by total reflection X-ray fluorescence, increased as the Cu 2+ concentration in solution increased. In dilute hydrofluoric acid, Cu 3+ addition had a significant and systematic effect on the corrosion potential and corrosion current density of silicon. However, in both types of solution, the cathodic current calculated from the measured copper deposition was found to be only a small fraction of the corrosion current (less than 1%). This indicates that the primary cathodic reaction is not copper ion reduction but hydrogen ion reduction. Illumination affected the electrochemical behavior of both p- and n-type silicon in Cu 2+ spiked dilute hydrofluoric acid, but only that of p-type silicon in buffered hydrofluoric acid.

The effect of copper contamination on field overlap edges and perimeter junction leakage current

This work demonstrates that copper contamination present on pre gate-oxidation silicon surfaces results in yield and reliability problems particularly at field overlap edges. Similarly, the junction leakage current associated with the junction perimeter dominates the total leakage current. These detrimental device effects are shown to be caused by copper that is present close to the silicon surface even after thermal processing. Because field overlap and junction perimeter defects become relatively more important when the critical dimensions of circuits are scaled to smaller sizes, they dominate yield loss of high-density circuits, magnifying their importance for future technology generations.

Analysis of Single Events Effects on Monolithic PLL Frequency Synthesizers

Frequency synthesizers are fundamental building blocks in radio frequency, communications, and analog signal processing for generating high accuracy oscillatory signals. In general, the frequency synthesizer is the most sensitive block in the system since many of the signal processing elements such as clock, filters, and up/down converters depend on the synthesizer generating a clean sinusoidal signal at the given frequency. For radiation environments, the response and the sensitivity of the phase-lock loop (PLL) and the synthesizer block is very critical. This paper examines the effect of single events (SEE) radiation on the PLL locking and steady state response. The PLL circuits operating at 2.4 GHZ were designed and fabricated using a 0.13mum CMOS process This paper presents the experimental and simulations results on the SEE radiation effects on the PLL

Electrochemical Impedance Spectroscopy of Copper Deposition on Silicon from Dilute Hydrofluoric Acid Solutions

Electrochemical impedance spectroscopy was used to probe the mechanism of copper deposition on silicon from dilute hydrofluoric acid solutions. Reaction parameters such as polarization resistance and space-charge capacitance were evaluated using an equivalent circuit model. The electrochemical impedance technique was found to be sensitive to parts per billion levels of Cu 2+ ion in dilute hydrofluoric acid solutions. An inductive loop appeared in Nyquist plots only when Cu 2+ ions were present in hydrofluoric acid solutions. Both the polarization resistance and inductance decreased significantly as the solution Cu 2+ concentration increased. Addition of a nonionic surfactant to hydrofluoric acid solutions significantly altered impedance characteristics of the silicon/solution interface. Total reflection X-ray fluorescence results showed that illumination enhanced deposition of copper on silicon nearly an order of magnitude.

SET tolerant CMOS comparator

A novel way to mitigate single event transients (SETs) in a comparator by using auto-zeroing techniques is presented. Two comparators, a folded cascode comparator and a novel auto-zeroed comparator, are simulated using a current pulse model for a single event strike. These simulations show that the novel auto-zeroed comparator transients are never longer in duration than a single auto-zero clock period. This compares favorably to a folded cascode comparator sample circuit, whose maximum transient duration is strongly dependent on the differential input voltage and can be four times as long. The use of the presented auto zero comparator can practically eliminate the comparator contribution to single event errors in many mixed signal circuits, such as analog-to-digital converters (ADCs).

A digitally controlled DC-DC buck converter with lossless load-current sensing and BIST functionality

Lossless load current sensing ability is one of the most desirable features of contemporary current- or voltage-mode-controlled DC-DC converters. Current sensing can be used for short circuit detection, multi-stage converter load balancing, thermal control, and load-independent control of DC-DC converters [1]. Recently, current sensing techniques using the existing inductor series DC resistance (DCR) are gaining attention due to their reduced complexity and minimized loss [2][4]. These techniques increase the need for inductor build-in self-test (BIST) ability to measure DCR. Inductor BIST is also critical for high-reliability applications such as automotive and aerospace systems where component variation and drift need to be closely monitored. An analog inductor characterization and current sensing technique utilizing Gm-C filtering is proposed in [2], where the gain errors and sensing offset are cancelled in analog domain. The DC-DC buck converter presented here uses an offset-independent inductor characterization enabling a digital continuous lossless load-current-sensing scheme. The proposed inductor BIST and current-sensing techniques can be extended to current-mode-controlled converters and multi-stage parallel converters as well.

Estimation and verification of radiation induced N/sub ot/ and N/sub it/ energy distribution using combined bipolar and MOS characterization methods in gated bipolar devices

Complementary bipolar and MOS characterization techniques, specifically the gate sweep (GS) and sub-threshold sweep (SS), are used to estimate the radiation induced oxide charge (N/sub ot/) and interface trap (N/sub it/) buildup in gated bipolar test devices. The gate sweep and sub-threshold sweep data from recent TID testing of gated lateral PNP devices suggests an asymmetric energy distribution of interface traps after ionizing radiation exposure. Charge pumping (CP) experiments were done on the test devices to estimate the energy distribution of interface traps induced by radiation. The CP results are used in this paper to confirm the analytical findings from the GS and SS techniques and solidify the use of the complementary method as a simple way of determining radiation induced interface trap distribution in gated bipolar devices.

Modeling the Dose Rate Response and the Effects of Hydrogen in Bipolar Technologies

A physical model describing the dose rate response and the effect of hydrogen in bipolar technologies is presented. The model uses electron-hole pair recombination and competing hydrogen reactions to explain the behaviors of bipolar devices and circuits at different dose rates. Dose-rate-dependent computer simulations based on the model were performed, and the results provide excellent qualitative agreement with the dose rate data taken on both gated lateral pnp bipolar test transistors and LM193 bipolar dual-voltage comparators. The model presented in this paper can be used to explain a variety of factors that can influence device dose rate response in bipolar technologies.