Fengqi Zhang

Analysis of the TID Induced Failure Modes in NOR and NAND Flash Memories

The total ionizing radiation effects of several NOR and NAND flash memories under the read only mode are investigated. An X-ray microbeam test was also performed to help detect the radiation susceptibility of different circuits. The error distribution is mapped for the NOR flash memories, featuring significant address related signature. Relevant circuits are analyzed to address these failure modes.

Single-Event Multiple Transients in Conventional and Guard-Ring Hardened Inverter Chains Under Pulsed Laser and Heavy-Ion Irradiation

Single-event multiple transients (SEMTs) are investigated using an on-chip self-triggered circuit. Measured results for inverter chains of two layout designs, including a guard-ring design and a conventional design, are compared under pulsed laser and heavy-ion (Bi) irradiations. Pulsed laser exposures of different energies and Bi heavy-ion irradiation at different injection angles, including along the well direction and across the well direction, are found to produce SEMTs with different probabilities. The use of a guard-ring hardening technique is demonstrated to be very effective in reducing production of SEMTs for inverters without direct electrical connection. Charge sharing-induced SEMTs are found to have different pulsewidth distributions for angled ion incidence than normal ion or laser incidence.

Pattern dependence in synergistic effects of total dose on single-event upset hardness*

The pattern dependence in synergistic effects was studied in a 0.18 μm static random access memory (SRAM) circuit. Experiments were performed under two SEU test environments: 3 MeV protons and heavy ions. Measured results show different trends. In heavy ion SEU test, the degradation in the peripheral circuitry also existed because the measured SEU cross section decreased regardless of the patterns written to the SRAM array. TCAD simulation was performed. TID-induced degradation in nMOSFETs mainly induced the imprint effect in the SRAM cell, which is consistent with the measured results under the proton environment, but cannot explain the phenomena observed under heavy ion environment. A possible explanation could be the contribution from the radiation-induced GIDL in pMOSFETs.

Single-event multiple transients in guard-ring hardened inverter chains of different layout designs

Abstract Single-event multiple transients (SEMTs) measurement based on an on-chip self-triggered method is performed. Measurement results for guard-ring hardened inverter chains of two layout designs, including a source/drain sharing design and a conventional design, are compared under pulsed laser irradiation. Pulsed laser exposures with different energies show that the guard-ring hardened inverter chain with a source/drain sharing design is more sensitive to single-event double transients (SEDTs). It is found that SEDTs with small temporal differences can be merged into single-event single transients (SESTs) thanks to the pulse broadening effect. A layout-hardened design for SEDTs in the guard-ring hardened inverter chain is also suggested.

Synergistic effect of total ionizing dose on single event effect induced by pulsed laser microbeam on SiGe heterojunction bipolar transistor

The synergistic effect of total ionizing dose (TID) on single event effect (SEE) in SiGe heterojunction bipolar transistor (HBT) is investigated in a series of experiments. The SiGe HBTs after being exposed to Co-60 gamma irradiation are struck by pulsed laser to simulate SEE. The SEE transient currents and collected charges of the un-irradiated device are compared with those of the devices which are irradiated at high and low dose rate with various biases. The results show that the SEE damage to un-irradiated device is more serious than that to irradiated SiGe HBT at a low applied voltage of laser test. In addition, the gamma irradiations at forward and all-grounded bias have an obvious influence on SEE in the SiGe HBT, but the synergistic effect after cutting off the gamma irradiation is not significant. The influence of positive oxide-trap charges induced by TID on the distortion of electric field in SEE is the major factor of the synergistic effect. Moreover, the recombination of interface traps also plays a role in charge collection.

Modeling the impact of well contacts on SEE response with bias-dependent Single-Event compact model

Abstract With technology scaling, a common and efficient strategy to improve the soft error vulnerability of sensitive nodes is to place well/substrate contacts frequently. This paper reports a revised method to integrate the impact of well contacts on SEE response with the bias-dependent SE compact model for circuit simulation. After modifying the SE sub-circuit with resistors and current source placed between the n-well and p-well contacts and then calibrating the parameters by layout-level TCAD simulation results, the resulting model is able to evaluate the SEE vulnerability of devices and circuits with various well contacts. Besides, it is able to evaluate the hardness performance of well contact optimization before fabrication.

Ionizing radiation effect on single event upset sensitivity of ferroelectric random access memory

The impact of ionizing radiation effect on single event upset (SEU) sensitivity of ferroelectric random access memory (FRAM) is studied in this work. The test specimens were firstly subjected to 60Co γ-ray and then the SEU evaluation was conducted using 209Bi ions. As a result of TID-induced fatigue-like and imprint-like phenomena of the ferroelectric material, the SEU cross sections of the post-irradiated devices shift substantially. Different trends of SEU cross section with elevated dose were also found, depending on whether the same or complementary test pattern was employed during the TID exposure and the SEU measurement.