Wang Zujun

Degradation of CMOS APS Image Sensors Induced by Total Ionizing Dose Radiation at Different Dose Rates and Biased Conditions

The experiments of total ionizing dose radiation effects on CMOS APS image sensors at the dose rates of 50.0 and 0.2 rad(Si)/s were presented. The CMOS APS image sensors were manufactured using the standard 0.35 - μm CMOS technology that had a typical gate-oxide thickness of 7.0 nm. The samples were divided into two groups, with one group biased and the other unbiased during 60Coγ irradiation. When the samples were exposed to the total dose of 200 krad(Si), only one investigated device was still exposed up to the highest total dose of 800 krad(Si), and functional failure was observed. The dark signal ( KD), dark signal non-uniformity (DSNU), noise ( VN), saturation output signal voltage ( VS), and dynamic range (DR) versus the total doses were investigated. The tendency for KD, DSNU, and VN to increase at 50.0 rad(Si)/s is larger than that at 0.2 rad(Si)/s. The degradation mechanisms of CMOS APS image sensors were analyzed. The room temperature annealing tests were performed at 24 h, 48 h, and 168 h with different biased conditions after irradiation.

Different Dose Rate Radiation Effects on Linear CCDs

Charge coupled devices (CCD) have been tested at widely differing dose rates to examine the radiation tolerance dependence on the dose rates. The test results show a maximum tolerance of CCDs at 10.2 rad(Si)/sec, a slight reduction in tolerance at 34.8 rad(Si)/sec and a quite precipitous roll off when moving down to 1 rad(Si)/sec and 0.1 rad(Si)/sec. The degradation of the dummy output voltages and the dark signal voltages are compared at the dose rates of 0.1,1.0,10.2 and 34.8 rad(Si)/sec, respectively. It shows that the degradation levels depend on the dose rates. The CCDs are divided into two groups during 60Co γ irradiation. Either the output amplifiers or the photo sensing and the shift register areas are shielded with Pb during the irradiation tests.

The research status and challenge of space radiation physics and application

Space radiation physics and application include the theory and the key technologies of studying radiation effects in spacecraft electronics systems and improving the on-orbit survival probability of spacecrafts. It is an interdisciplinary science involving nuclear science and astronautics electronics. The research work mainly covers simulation of radiation environment, interaction between radiation and materials, radiation hardening, as well as radiation measurement and diagnosis. In recent years, new challenges and problems to the research of space radiation physics have arisen along with the rapid development in microelectronics and space technology. Radiation effects, including single event effects, total ionizing dose effects, displacement damage, charging and discharging effects, are one kind of main threats for space applications. The study of space radiation physics and application plays a fundamental role in maintaining the robustness against radiation of the spacecraft electronics systems. Countries like America and Russia have devoted a lot in this field, now they have a whole set of facilities, guidelines and principles to guarantee the fabrication, evaluation, and utilization of the radiation-hardened electronic devices and systems. However, there are still some problems left unsolved. Furthermore, as the fast development of the electronics, new problems emerge quickly. Space radiation environments mainly include the Van Allen trapped belt, Solar cosmic rays, galactic particles. The fluence of the related protons, electrons, and heavy ions are strongly dependent on solar activity and geomagnetic activity. The distribution of particle fluence is highly no uniform. Spacecraft working in different orbits may face diverse radiation environments. To describe the radiation environments, series of models have been developed for describing the distribution of trapped protons and electrons. Although continued being modified, the errors between predicted values and measured ones are still quite large. It is essential to keep working on this area and increase the accuracy. To measure the parameters like categories, fluence, energy and flux of the radiation environments, many types of detectors have been developed. Along with the emergence of new types of material, it is always meaningful to keep improving the performance and efficiency of detectors. Exploring the underlying mechanisms of radiation effects is extremely important for carrying out the research on radiation hardening by design. In the past 50 years, more and more work has been devoted to studying the physical mechanisms and gained valuable results. However, we still do not get the clear whole physical pictures of some well-known effects. Meanwhile, more and more electronic devices with new material and new structures bring new challenge to the mechanism study. To make sure that an electronic system is robust enough to radiation environments, it is necessary to quantify the radiation vulnerability of every electronic device in the system. Through circuit or system simulation, the radiation vulnerability of the whole system can be estimated. At present, it is still difficult to perform this kind of simulation accurately. This paper discusses the present status and developments tendency in simulating the space radiation environment, developing laboratory simulation equipments, measuring radiation field, researching radiation effects and mechanism, estimating and testing radiation effects, hardening electronics devices, etc. Furthermore, the key and basic problems in this field were discussed. The corresponding advices of space radiation physics and application were proposed.

Study of the dose rate effect of 180 nm nMOSFETs

Radiation induced offstate leakage in the shallow trench isolation regions of SIMC 0.18 ?m nMOSFETs is studied as a function of dose rate. A ?true? dose rate effect (TDRE) is observed. Increased damage is observed at low dose rate (LDR) than at high dose rate (HDR) when annealing is taken into account. A new method of simulating radiation induced degradation in shallow trench isolation (STI) is presented. A comparison of radiation induced offstate leakage current in test nMOSFETs between total dose irradiation experiments and simulation results exhibits excellent agreement. The investigation results imply that the enhancement of the leakage current may be worse for the dose rate encountered in the environment of space.

Total ionizing dose radiation effects on NMOS parasitic transistors in advanced bulk CMOS technology devices

In this paper, total ionizing dose effect of NMOS transistors in advanced CMOS technology are examined. The radiation tests are performed at 60 Co sources at the dose rate of 50 rad (Si)/s. The investigations results show that the radiation-induced charge buildup in the gate oxide can be ignored, and the field oxide isolation structure is the main total dose problem. The total ionizing dose (TID) radiation effects of field oxide parasitic transistors are studied in detail. An analytical model of radiation defect charge induced by TID damage in field oxide is established. The I- V characteristics of the NMOS parasitic transistors at different doses are modeled by using a surface potential method. The modeling method is verified by the experimental I- V characteristics of 180 nm commercial NMOS device induced by TID radiation at different doses. The model results are in good agreement with the radiation experimental results, which shows the analytical model can accurately predict the radiation response characteristics of advanced bulk CMOS technology device.

Dose Rate and Bias Effects on COTS Array CCDs Induce Dark Signals Increase

The experiments of dose rate and bias effects on commercial-off-the-shelf array charge-coupled devices (CCDs) are presented. The dark signal ( VD) is calculated with the output signal voltages measured at different integration times when no light is incident on the CCDs. The dark signal voltages ( VD) versus the total dose at the dose rates of 0.01, 0.1, 1.0, 10.0, and 50 rad(Si)/s are compared. Annealing tests are performed to eliminate the time-dependent effects. Degradation levels were found to depend on the dose rates. The CCDs are divided into two groups-with one group biased and the other unbiased during 60Coγ irradiation. The biased CCDs are shown to degrade more severely than the unbiased CCDs.

Research progress of radiation effects mechanisms and experimental techniques in nano-devices

Radiation damage in electronic devices is one of the key factors determining the survival probability of on-orbit spacecraft. Thus, it has remained an important topic in the field of radiation-hardening technology. High reliability, high integration, high performance, low power consumption, and low cost are the important requirements for the development of next-generation electronic systems. For space electronic systems, the use of radiation-hardened high-performance nano-devices will continue to be an important trend. Based on thorough reviewing of the research status at home and abroad, this paper analyzes new problems faced by nano-devices due to radiation. Nano-device technology is different from that for macroscopic devices. For example, the channel length in nano-devices is reduced to ten nanometers, and the equivalent thickness of their gate oxide is less than one nanometer. In order to reduce the gate-induced drain leakage effect, either vertical inverse doping or transverse halo ring doping is applied to the process. To reduce power consumption, multiple semiconductor materials, such as strained silicon, GeSi, high k gate dielectric, metal gate, etc., have been introduced. To enhance control over the gate, the structure incorporates 3D FinFETs. This process approaches the physical limit, and the adoption of new materials and structures have created new radiation effects and mechanisms. Thus, the experimental techniques become more complex, which brings new challenges to research on radiation-hardening technology. This paper analyzes the present status of domestic and foreign research into radiation effects in nano-devices. Key scientific issues and technologies will be presented, which are needed to study radiation effects and simulation experiments of nano-devices with a feature size of less than 28 nm. Research on photon and heavy ion radiation mechanisms, as well as experimental techniques in nano-devices, should continue receiving focus. In addition, radiation damage mechanisms in nanometer devices should be studied. Heavy-ion micro-beam simulations for the distribution of nano-devices and circuit sensitive areas should be established in order to analyze weak links. A new nano-device and circuit radiation-resistant design method should be proposed. The current survey provides a reference for anti-radiation reinforcement and applications of nano-devices in space.

Simulation for signal charge transfer of charge coupled devices

Physical device models and numerical processing methods are presented to simulate a linear buried channel charge coupled devices (CCDs). The dynamic transfer process of CCD is carried out by a three-phase clock pulse driver. By using the semiconductor device simulation software MEDICI, dynamic transfer pictures of signal charges cells, electron concentration and electrostatic potential are presented. The key parameters of CCD such as charge transfer efficiency (CTE) and dark electrons are numerically simulated. The simulation results agree with the theoretic and experimental results.