Fan Ruyu

Worst-case total dose radiation effect in deep-submicron SRAM circuits

The worst-case radiation effect in deep-submicron SRAM (static random access memory) circuits is studied through theoretical analysis and experimental validation. Detailed analysis about the radiation effect in different parts of circuitry is presented. For SRAM cells and a sense amplifier which includes flip-flop structures, their failure level against ionizing radiation will have a connection with the storage state during irradiation. They are inclined to store or read the same state as the one stored during irradiation. Worst-case test scheme for an SRAM circuit is presented, which contains a write operation that changes the storage states into the opposite ones after irradiation and then a read operation with opposite storage states. An irradiation experiment is designed for one 0.25 μm SRAM circuit which has a capacity of 1 k × 8 bits. The failure level against ionizing radiation concluded from this test scheme (150 krad(Si)) is much lower than the one from the simplest test scheme (1 Mrad(Si)). It is obvious that the failure level will be overestimated if the simplest test scheme is chosen as the test standard for SRAM circuits against ionizing radiation.

Study of radiation-induced leakage current between adjacent devices in a CMOS integrated circuit

Radiation-induced inter-device leakage is studied using an analytical model and TCAD simulation. There were some different opinions in understanding the process of defect build-up in trench oxide and parasitic leakage path turning on from earlier studies. To reanalyze this problem and make it beyond argument, every possible variable is considered using theoretical analysis, not just the change of electric field or oxide thickness independently. Among all possible inter-device leakage paths, parasitic structures with N-well as both drain and source are comparatively more sensitive to the total dose effect when a voltage discrepancy exists between the drain and source region. Since N-well regions are commonly connected to the same power supply, these kinds of structures will not be a problem in a real CMOS integrated circuit. Generally speaking, conduction paths of inter-device leakage existing in a real integrated circuit and under real electrical circumstances are not very sensitive to the total ionizing dose effect.

A CVD diamond film detector for pulsed proton detection

A chemical vapour deposition (CVD) diamond film detector was prepared and the main characteristics for pulsed proton detection were studied at Beijing Tandem Accelerator. The result shows that the charge collection efficiency of the detector increases with increasing electric field intensity and reaches to 9.44% at 5 V/μm with the charge collection distance of 15.9 μm. The relationship between the sensitivity of the detector and proton energy is consistent with the Monte Carlo (MC) simulation result. Its plasma time for a pulse with 4.85×105 protons is 11.2ns. The dose threshold for onset of damage under 9MeV proton irradiation in the detector is about 1013 cm−2. All of the results show that a CVD diamond detector has fast time response and high radiation hardness, and can be used in pulsed proton detection.

Numerical studies on resonant and enhancement effects for coupling of microwave pulses into narrow slots

In this paper, modifications to the finite-difference time-domain(FD-TD) method for modeling microwave pulse coupling into a slot, which is much narrower than one conventional FD-TD cell, are discussed. The coupling process of microwave pulse into a slot is studied by using the modified FD-TD method, and the dependence of microwave coupling on slot sizes, the carrier frequencies and the polarization directions of the incident waves is analysed. Resonant and enhancement effects which occur in this process are observed. The condition at which the resonant effect takes place is also presented.

First principles simulation technique for characterizing single event effects

This paper develops a new simulation technique to characterize single event effects on semiconductor devices. The technique used to calculate the single event effects is developed according to the physical interaction mechanism of a single event effect. An application of the first principles simulation technique is performed to predict the ground-test single event upset effect on field-programmable gate arrays based on 0.25 μm advanced complementary metal—oxide—semiconductor technology. The agreement between the single event upset cross section accessed from a broad-beam heavy ion experiment and simulation shows that the simulation technique could be used to characterize the single event effects induced by heavy ions on a semiconductor device.

Synergistic effects of neutron and gamma ray irradiation of a commercial CHMOS microcontroller

This paper presents the experimental results of a combined irradiation environment of neutron and gamma rays on 80C196KC20, which is a 16-bit high performance member of the MCS96 microcontroller family. The electrical and functional tests were made in three irradiation environments: neutron, gamma rays, combined irradiation of neutron and gamma rays. The experimental results show that the neutron irradiation can affect the total ionizing dose behaviour. Compared with the single radiation environment, the microcontroller exhibits considerably more severe degradation in neutron and gamma ray synergistic irradiation. This phenomenon may cause a significant hardness assurance problem.

Scaling effects of single-event gate rupture in thin oxides

The dynamics of the excess carriers generated by incident heavy ions are considered in both SiO2 and Si substrate. Influences of the initial radius of the charge track, surface potential decrease, external electric field, and the LET value of the incident ion on internal electric field buildup are analyzed separately. Considering the mechanisms of recombination, impact ionization, and bandgap tunneling, models are verified by using published experimental data. Moreover, the scaling effects of single-event gate rupture in thin gate oxides are studied, with the feature size of the MOS device down to 90 nm. The value of the total electric field decreases rapidly along with the decrease of oxide thickness in the first period (12 nm to 3.3 nm), and then increases a little when the gate oxide becomes thinner and thinner (3.3 nm to 1.8 nm).

Influence of the work function on the electric field at the cathode surface in a diode

The cathode plays an important role in high power microwave devices, the paper studies the time-dependence laws of the electric field at the cathode surface in a planar vacuum diode with a field emission cathode. The influence of the work function on the electric field at the cathode surface has been investigated. To analyze the effects of the space charge of emitted electrons on the electric field at the cathode surface, Poissons equation was solved numerically for different parameters of applied electric field in a finite-difference time-domain particle in cell simulation. It has been shown that the self-consistent electric field at the cathode surface oscillates initially and finally yields a steady state, the increase in the value of work function results not only in an decrease in the absolute steady value of the electric field at the cathode surface, but also in an shorter time which is cost to reach the steady state for it.

Time-domain volume integral equation for transient scattering from inhomogeneous objects—2D TE case

This letter proposes a time-domain volume integral equation based method for analyzing the transient scattering from a 2D inhomogeneous cylinder by involking the volume equivalence principle for the transverse electric case. This integral equation is solved by using an MOT scheme. Numerical results obtained using this method agree very well with those obtained using the FDTD method.