Hugh J. Barnaby

Enhanced TID Susceptibility in Sub-100 nm Bulk CMOS I/O Transistors and Circuits

This paper evaluates the radiation responses of 2.5 V I/O transistors and regular-threshold MOSFETs from a 90 nm commercial bulk CMOS technology. The data obtained from Co ionizing radiation experiments indicate enhanced TID susceptibility in I/O devices and circuits, which is attributed to the p-type body doping. A quantitative model is used to analyze the effects of doping and oxide trapped charge buildup along the sidewall of the shallow trench isolation oxide. These effects are captured in the general electrostatic equation for surface potential, which can be correlated to off-state leakage current. Device simulations are used in concert with experimental measurements and the analytical model to provide physical insight into the radiation response of each device type.

Total ionizing dose effects in shallow trench isolation oxides

The peaked evolution of leakage current with total ionizing dose observed in transistors in 130 nm generation technologies is studied with field oxide field effect transistors (FOXFETs) that use the shallow trench isolation as gate oxide. The overall radiation response of these structures is determined by the balance between positive charge trapped in the bulk of the oxide and negative charge in defect centers at its interface with the silicon substrate. That these are mostly interface traps and not border traps is demonstrated through dynamic transconductance and variable-frequency charge-pumping measurements. These interface traps, whose formation is only marginally sensitive to the bias polarity across the oxide, have been observed to anneal at temperatures as low as 80 °C. At moderate or low dose rate, the buildup of interface traps more than offsets the increase in field oxide leakage due to oxide-trap charge. Consequences of these observations for circuit reliability are discussed.

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.

The Effects of Hydrogen on the Enhanced Low Dose Rate Sensitivity (ELDRS) of Bipolar Linear Circuits

It is experimentally demonstrated with test transistors and circuits that hydrogen is correlated with enhanced low dose rate sensitivity (ELDRS) in bipolar linear circuits. These experiments show that the amount of hydrogen determines the total dose response versus dose rate, both the saturation at low dose rate and the transition dose rate between the high and low dose rate responses. The experimental results are supported with modeling calculations using REOS (radiation effects in oxides and semiconductors).

Gate-Length and Drain-Bias Dependence of Band-to-Band Tunneling-Induced Drain Leakage in Irradiated Fully Depleted SOI Devices

The effects of gate length and drain bias on the off-state drain leakage current of irradiated fully-depleted SOI n-channel MOSFETs are reported. The experimental results are interpreted using a model based on the combined effects of band-to-band tunneling (BBT) and the trapped charge in the buried oxide. For negative gate-source voltages, the drain leakage current increases with the drain voltage because the electric field in the gate-to-drain overlap region is increasing. The off-state current in these devices increases with total ionizing dose due to oxide trapped charge build up in the buried oxide, enhanced by the BBT mechanism. The experimental data show that these effects are more significant for devices with shorter gate-lengths. Simulation results suggest that the BBT-generated holes are more likely to drift all the way from the drain to the source in shorter devices, enhancing the drain leakage current, while they tend to tunnel across the gate oxide in longer devices.

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.

Impact of Alpha Particles on the Electrical Characteristics of TiO

Titanium-oxide (TiO2 ) memristors exposed to 1-MeV alpha particles exhibit only minor changes in the electrical response for ion fluencies up to 1014 cm - 2. At higher fluence levels, virgin and off-state devices exhibit measurable increases in current conduction between the two platinum (Pt) electrodes. Analysis, supported by radiation transport and numerical device simulations, suggests that radiation-induced displacement damage in the TiO2 film increases the density of oxygen vacancies, thereby altering both resistivity in the bulk of the transition-metal oxide and the junction characteristics of Pt-TiO2 interface. Nevertheless, the experimental results indicate continued switching functionality of the memristors even after exposure to 1015 cm- 2 alpha particles. The high intrinsic vacancy density in the devices prior to radiation exposure is identified as the primary feature contributing to apparent radiation hardness.

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It is demonstrated with test transistors and circuits that a small amount of hydrogen trapped in hermetically sealed packages can significantly degrade the total dose and dose rate response of bipolar linear microelectronics. In addition, we show that when exposed to an atmosphere of 100% molecular hydrogen dies with silicon nitride passivation are unaffected, whereas dies with silicon carbide or deposited oxides become very soft at high and low dose rate.

Memristors

The total ionizing dose (TID) effect of gamma-ray (γ-ray) irradiation on HfOx based resistive random access memory was investigated by electrical and material characterizations. The memory states can sustain TID level ∼5.2 Mrad (HfO2) without significant change in the functionality or the switching characteristics under pulse cycling. However, the stability of the filament is weakened after irradiation as memory states are more vulnerable to flipping under the electrical stress. X-ray photoelectron spectroscopy was performed to ascertain the physical mechanism of the stability degradation, which is attributed to the Hf-O bond breaking by the high-energy γ-ray exposure.

The Effects of Hydrogen in Hermetically Sealed Packages on the Total Dose and Dose Rate Response of Bipolar Linear Circuits

Programmable metallization cells (PMCs) are emerging ReRAM devices exhibiting resistance switching due to cation transport in a solid-state electrolyte and redox reactions at the electrodes. Their non-volatility and low power requirements have led to increased interest in their development for non-volatile memory applications. Investigation of the total dose response of PMCs will contribute to our understanding of radiation induced effects in these novel memory devices as well as assess their suitability for use in ionizing radiation environments. This work investigates the impact of total ionizing dose on the switching characteristic of silver doped Ge30Se70 PMC memory devices. The results obtained show that the resistance switching characteristic of these cells which use a solid state electrolyte based on Ge30Se70 is not affected by a total dose exposure of up to 10 Mrad( Ge30Se70).