Total Dose Radiation Hardness Research Articles

Programming mechanism and characteristics of Sense-Switch pFlash cells

Sense-Switch pFlash is a common floating gate switching cell with the advantages of high integration, natural field-edge total dose radiation hardness, and high reliability. It is the core configuration cell of the field-programmable gate array (FPGA), and it can be used to realize radiation-hardened flash-based FPGA circuits. This study investigates the programming mechanism of the Sense-Switch pFlash device with dumbbell structure based on 0.13 μm eFlash technology and analyzes the influences of the device's programming and erasing methods on the threshold characteristics, on/off-state characteristics, and retention characteristics of Sense-Switch pFlash cells. It is found that there are multiple mechanisms in the programming process. Additionally, under certain programming and erasing voltage conditions, the threshold voltage and driving current of programming/erasing state depend on the pulse width, meaning that a fixed pulse width leads to specific threshold voltage and driving current values in the programming and erasing modes, which is called the pulse width modulation effect (PWME). Multi-level storage can be well obtained to expand the application of the Sense-Switch pFlash in the field of computing-in-memory and brain-inspired computing.

Enhanced Radiation Hardness in SOI MOSFET with Embedded Tunnel Diode Layer

This paper presents an improved body tie structure for partially depleted silicon-on-insulator (SOI) MOSFETs. Inspired by tunneling current of degenerated p-n-junction at low forward bias, a tunnel diode layer is inserted at back channel forming a new type of body tie. The tunnel diode layer can be prepared either by ion implantation or in situ silicon deposition, which is fully compatible with present commercial SOI processes. The introduced body contact serves as an additional current flowing path for accumulated majority carriers generated by impact ionization or heavy-ion radiation, reducing critical floating body effects. The heavily doped tunnel diode layer extending from source to drain improves total dose radiation hardness and suppresses front-back channel coupling of SOI MOSFET for increasing back-gate threshold voltage and reduced width of space charge region. Experimental and simulation results validate the usefulness of the introduced body tie in enhancing radiation hardness of SOI transistor comparing with the conventional floating body devices. Therefore, SOI device with embedded tunnel diode layer can be considered as a promising candidate in spaceborne applications.

The radiation hardness of the nitrogen-fluorine implanted buried oxide layer in silicon-on-insulator materials against higher total dose irradiation

Nitrogen (N) and fluorine (F) ions were sequentially implanted into the buried oxide (BOX) to improve the total dose radiation hardness of the BOX layer in silicon-oninsulator (SOI) materials. The radiation response of the BOX layers modified by the ion implantation was characterized by flat-band voltage shifts and trapped charge changes in the BOX, based on the capacitance-voltage (C-V) measurements on the polysilicon-BOX-semiconductor (PBS) structures fabricated on the SOI materials, before and after irradiation using Co-60 γ rays with various doses range from 0.7 to 1.7 Mrad(Si). The experimental results show that a considerably enhanced hardness for the BOX layer can be achieved by this co-implantation of nitrogen and fluorine on proper process conditions, and the radiation responses of the BOX layers are directly associated with the anneal times after nitrogen implantation. In particular, the rebound and fluctuation phenomena of the BOX radiation response were observed with increasing dose, according to the changes in the flat-band voltages, which cannot be explained in terms of the increase in radiation induced interface state density, and the related mechanisms were analyzed and discussed.

Effect of co-implantation of nitrogen and fluorine on the fixed positive charge density of the buried oxide layer in SIMOX SOI materials

Nitrogen ions implanted into the buried oxide layer can increase the total dose radiation hardness of silicon on insulator (SOI) materials. However, the obvious increase in positive charge density in the buried layer with high dose of nitrogen implantation leads to a negative effect on the technology of nitrogen implantation into buried oxide. In order to suppress the increase in positive charge density in the nitrogen-implanted buried layer, co-implantation of nitrogen and fluorine is used to implant fluorine into the nitrogen-implanted buried layer. High-frequency voltage-capacitance (C-V) technique is used to characterize the positive charge density in the buried layer. Results show that, in most cases, using the co-implantation of nitrogen and fluorine can significantly reduce the positive charge density in the nitrogen-implanted buried layer. At the same time, it is also found that further increase of the positive charge density induced by fluorine implantation in the nitrogen-implanted buried layer can occur in particular cases. It is proposed that the decrease in the positive charge density in the fluorine and nitrogen-implanted buried layer is due to the introduction of electron traps into the buried layer through fluorine implantation.

Influence of nitrogen implantation into the buried oxide on the radiation hardness of silicon-on-insulator wafers

In order to improve the total-dose radiation hardness of the buried oxide of separation by implanted oxygen silicon-on-insulator wafers, nitrogen ions were implanted into the buried oxide with a dose of 1016 cm−2, and subsequent annealing was performed at 1100 °C. The effect of annealing time on the radiation hardness of the nitrogen implanted wafers has been studied by the high frequency capacitance-voltage technique. The results suggest that the improvement of the radiation hardness of the wafers can be achieved through a shorter time annealing after nitrogen implantation. The nitrogen-implanted sample with the shortest annealing time 0.5 h shows the highest tolerance to total-dose radiation. In particular, for the 1.0 and 1.5 h annealing samples, both total dose responses were unusual. After 300-krad(Si) irradiation, both the shifts of capacitance-voltage curve reached a maximum, respectively, and then decreased with increasing total dose. In addition, the wafers were analysed by the Fourier transform infrared spectroscopy technique, and some useful results have been obtained.

Gamma-ray irradiation effects on the interface states of MIS structures

Gamma-ray irradiation effects on the interface states of Au/SiO 2/n-Si (MIS) structures have been determined from capacitance–voltage ( C– V) and conductance–voltage ( G/ ω– V) measurements. The MIS structures were irradiated with gamma-rays at doses up to 100 kGy. The C–V and G/ ω– V characteristics were measured at high frequency (1 MHz) and room temperature before and after 60Co γ-ray irradiation. The obtained results showed that the barrier height ( Φ b) decreases with increasing radiation dose, while the interface states ( N ss) and depletion layer width ( W D) increase with the increase in radiation dose obtained from reverse bias C– V measurements. After γ irradiation, the decrease in capacitance and conductance of MIS structure result in the increase in the semiconductor depletion width. In addition, the voltage dependency of the series resistance ( R s) profile for various radiation doses was obtained from admittance-based measurement method. In addition, the high frequency (1 MHz) capacitance and conductance values measured under both reverse and forward bias have been corrected for the effect of R s to obtain the real capacitance of MIS structure. Experimental results indicate that the total dose radiation hardness of MIS structures may be limited by the decisive properties of the SiO 2/Si interface to radiation-induced damage.

Effects of γ-ray irradiation on the C–V and G/ω–V characteristics of Al/SiO2/p-Si (MIS) structures

The effect of the 60Co (γ-ray) exposure on the electrical characteristics of Al/SiO2/p-Si (MIS) structures has been investigated using capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements. The MIS structures were stressed with a bias of 0V during 60Coγ-sources irradiation with the total dose range from 0 to 25kGy. The C–V and G/ω–V characteristics were measured at 500kHz and room temperature before and after 60Coγ-ray irradiation. The results indicated that γ-irradiation caused an increase in the barrier height ΦB, interface states Nss and depletion layer width WD obtained from reverse bias C–V measurements. The series resistance Rs profile for various radiation doses was obtained from forward and reverse bias C–V and G/ω–V measurements. Both C–V and G/ω–V characteristics indicate that the total dose radiation hardness of MIS structures may be limited by the decisive properties of the SiO2/Si interface to radiation-induced damage. After γ-irradiation, the decrease in capacitance of MIS structure results in the increase in the semiconductor depletion width.

Effect of nanoclusters induced by Si implantation on total dose radiation response of a SOI wafer

Si ion implantation with subsequent annealing was used to improve the irradiation hardness of SOI wafers. The reduced negative shifts in the threshold voltage of the n-channel transistors showed that the total dose radiation hardness was remarkably enhanced by this modification process, and the pseudo-MOS method was used to test the Id–VG characteristics of the SOI samples before and after irradiation. Photoluminescence (PL) spectra demonstrated that Si nanoclusters were formed during annealing in the buried oxide of the implanted samples, which were possibly the main candidates for charge compensation. X-ray photoelectron spectroscopy (XPS) results also suggested that reduction of the threshold voltage shifts was accompanied with the formation of Si nanoclusters near the peak of the implants. Furthermore, the effect of positive charge buildup can be partly reduced as a result of the improvement on proton trapping in the bulk of the oxide due to the implantation induced nanoclusters.

Effects of illumination and 60Co γ-ray irradiation on the electrical characteristics of porous silicon solar cells

A new approach for hybrid metal–insulator–semiconductor (MIS) Si solar cells is adopted by Institute of Fundamental Problems for High Technology, Ukrainian Academy of Sciences. In order to interpret the effect of illumination and 60Co γ-ray radiation dose on the electrical characteristics of solar cells are studied at room temperature. Before the solar cells are subjected to stressed irradiation six different illumination levels of forward and reverse bias I– V measurements are carried out at room temperature. The solar cells are irradiated with 60Co γ-ray source irradiation, with a dose rate of 2.12 kGy/h and an over dose range from 0 to 500 kGy. Experimental results shows that both the values of capacitance and conductance increase with increasing illumination levels and give the peaks at high illumination levels. γ-ray irradiation induces an increase in the barrier heights Φ b( C– V) which are obtained from reverse-bias C– V measurements, whereas barrier heights Φ b( I– V) which are deducted from forward-bias I– V measurements remain essentially constant. This negligible change of Φ b( I– V) is attributed to the low barrier height (BH) in regions associated with the surface termination of dislocations. Both the I– V and C– V characteristics indicate that the total-dose radiation hardness of the Si solar cells cannot be neglected according to illumination levels.

Effects of beta-ray irradiation on the C–V and G/ω–V characteristics of Au/SiO2/n-Si (MOS) structures

The effects of β-ray irradiation on the electrical characteristics of Au/SiO2/n-Si (MOS) structures have been investigated using capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements. The MOS structures were irradiated with beta rays at doses up to 30kGy. The C–V and G/ω–V characteristics were measured at high frequency (1MHz) and room temperature before and after β-ray irradiation. The obtained results showed that β-irradiation resulted in an increase in the barrier height ΦB, interface states Nss and depletion layer width WD obtained from reverse bias C–V measurements. In addition, the voltage dependency of the series resistance Rs profile for various radiation doses was obtained from admittance-based measurement method of (C–V and G/ω–V). Both C–V and G/ω–V characteristics indicate that the total dose radiation hardness of MOS structures may be limited by the decisive properties of the SiO2/Si interface to radiation-induced damage.

A study on the total-dose response for modified silicon-on-insulator materials with the pseudo-MOS method

In this work, silicon-on-insulator wafers fabricated by the separation-by-implantation-of-oxygen method were modified by Si ion implantation to improve their total-dose radiation hardness. The chemical bonds of Si in the buried oxide layer were investigated using x-ray photoelectron spectroscopy. The results of Si 2p were presented to demonstrate the mechanism of radiation hardness with the formation of Si nanocrystals by ion implantation with the post anneal process. The pseudo-MOS method was used to test the ID–VG characteristics of the wafers before and after irradiation. The results showed that the processes of the buried oxide affected the character of the I–V curves of the pseudo-MOS, and a proper modification technology could improve the radiation hardness of the material remarkably.

Effects of 60Co γ-ray irradiation on the electrical characteristics of Au/n-GaAs (MS) structures

In order to interpret the effect of 60Co γ-ray radiation dose on the electrical characteristics of metal–semiconductor (Au/n-GaAs) Schottky barrier diodes (SBDs), these devices were stressed with a zero bias during 60Co γ-ray source irradiation with the dose rate 2.12 kGy h −1 and the total dose range was 0–500 kGy at room temperature. Experimental results show that γ-irradiation induces an increase in the barrier height Φ b( C–V) obtained from reverse-bias C–V measurements, whereas barrier height Φ b( I–V) obtained from forward-bias I–V measurements remained essentially constant. This negligible change of Φ b( I–V) is attributed to the low barrier height in regions associated with the surface termination of dislocations. The experimental I–V and C–V characteristics prove that there is a reaction for extra recombination centers in case of SBDs exposed to γ-ray radiation. Also, the ideality factor n and donor concentration decrease with increasing dose rate. Both I–V and C–V characteristics of the Schottky diode indicate that the total dose radiation hardness of GaAs devices may be limited by the susceptibility of the Au–GaAs interface to radiation-induced damage. The density of interface states N SS distribution profiles as a function E CC– E SS for each dose rate was extracted from the forward-bias I–V characteristics taking into account the bias dependence of the effective barrier height Φ e at room temperature. N SS decreases with increasing dose rate and above 250 kGy it remains constant. Such a behavior of N SS is attributed to the existence of the native insulator layer between the metal and semiconductor that passivates the surface of semiconductor, and thus the increase of the N SS.

Improvement of the radiation hardness of SIMOX buried layers using nitrogen implantation

An investigation of hardening the buried oxides (BOX) in separation by implanted oxygen (SIMOX) silicon-on-insulator (SOI) wafers to total-dose irradiation has been made by implanting nitrogen into the BOX layers with a constant dose at different implantation energies. The total-dose radiation hardness of the BOX layers is characterized by the high frequency capacitance–voltage (C–V) technique. The experimental results show that the implantation of nitrogen into the BOX layers can increase the BOX hardness to total-dose irradiation. Particularly, the implantation energy of nitrogen ions plays an important role in improving the radiation hardness of the BOX layers. The optimized implantation energy being used for a nitrogen dose, the hardness of BOX can be considerably improved. In addition, the C–V results show that there are differences between the BOX capacitances due to the different nitrogen implantation energies.

Noise performance of 0.35-/spl mu/m SOI CMOS devices and micropower preamplifier following 63-MeV, 1-mrad (Si) proton irradiation

Total dose and single-event radiation hardness, and operation over extreme temperatures make silicon-on-insulator (SOI) complementary metal oxide semiconductor (CMOS) processes leading contenders for space applications. This paper reports noise degradation of 0.35-/spl mu/m partially-depleted SOI CMOS devices and a micropower, low-noise preamplifier following 63-MeV proton irradiation to 1Mrad (Si). Proton irradiation, relevant for space mission environments, was considered since it induces both ionizing and displacement damage. Preamplifier input-referred white-noise voltage was minimized at low power consumption by operating input devices in moderate inversion for high transconductance efficiency. Flicker-noise, important for gyros and other mission sensors having low-frequency outputs, was minimized by large-area pMOS input devices and careful management of noninput devices. Measured 1-Hz gate-referred, flicker-noise voltage density increased 24 and 32% for pMOS and nMOS test devices respectively following 1 Mrad (Si) irradiation. Measured 1-Hz input-referred noise voltage density increased 22% between a nonirradiated and radiated preamplifier sample, which agrees closely with the 24% increase expected since noise is dominated by pMOS input devices. Device small-signal transconductance and white-noise were largely unchanged while output conductance appeared to increase over a factor-of-three. This suggests a modest design margin is required to maintain flicker noise performance, while substantial design margin may be required to maintain open-loop voltage gain.

Identification of radiation-induced parasitic leakage paths using light emission microscopy

Eliminating radiation-induced parasitic leakage paths in integrated circuits (ICs) is key to improving their total dose hardness. Semiconductor manufacturers can use a combination of design and/or process techniques to eliminate known radiation-induced parasitic leakage paths. However, unknown or critical radiation-induced parasitic leakage may still exist on fully processed ICs and it is extremely difficult (if not impossible) to identify these leakage paths based on radiation induced parametric degradation. We show that light emission microscopy can be used to identify the location of radiation-induced parasitic leakage paths in ICs. This is illustrated by using light emission microscopy to find radiation-induced parasitic leakage paths in partially-depleted silicon on insulator static random-access memories (SRAMs). Once leakage paths were identified, modifications were made to the SRAM design to improve the total dose radiation hardness of the SRAMs. Light emission microscopy should prove to be an important tool for the development of future radiation hardened technologies and devices.

/sup 60/Co gamma irradiation effects on n-GaN Schottky diodes

The effect of /spl gamma/-ray exposure on the electrical characteristics of nickel/n-GaN Schottky barrier diodes has been investigated using current-voltage (I-V), capacitance-voltage (C-V), and deep-level transient spectroscopy (DLTS) measurements. The results indicate that /spl gamma/-irradiation induces an increase in the effective Schottky barrier height extracted from C-V measurements. Increasing radiation dose was found to degrade the reverse leakage current, whereas its effect on the forward I-V characteristics was negligible. Low temperature (/spl les/50) post-irradiation annealing after a cumulative irradiation dose of 21 Mrad(Si) was found to restore the reverse I-V characteristics to pre-irradiation levels without significantly affecting the radiation-induced changes in C-V and forward I-V characteristics. Three shallow radiation-induced defect centers with thermal activation energies of 88 104 and 144 meV were detected by DLTS with a combined production rate of 2.12 /spl times/ 10/sup -3/ cm/sup -1/. These centers are likely to be related to nitrogen-vacancies. The effect of high-energy radiation exposure on device characteristics is discussed taking into account possible contact inhomogeneities arising from dislocations and interfacial defects. The DLTS results indicate that GaN has an intrinsically low susceptibility to radiation-induced material degradation, yet the effects observed in the Schottky diode I-V and C-V characteristics indicate that the total-dose radiation hardness of GaN devices may be limited by susceptibility of the metal-GaN interface to radiation-induced damage.

Total-dose radiation hardness assurance

Total-dose radiation hardness assurance is reviewed for MOS and bipolar devices and integrated circuits (ICs), with an emphasis on issues addressed by recent revisions to military and commercial standard test methods. Hardness assurance typically depends upon sample tests of a subgroup of devices or circuits to determine whether the full group meets its performance and functionality requirements to a desired confidence level. The dose rates of many standard test methods match neither the very high dose rates of some military environments nor the very low dose rates of most space environments. So, one must ensure that hardness assurance test plans address device response in the radiation environment of interest. An increasing emphasis has been placed over the last few decades on standardized test procedures to qualify devices for use in the natural space radiation environment. Challenging issues for defining test methods for space environments are nMOS transistor threshold-voltage rebound and enhanced low-dose-rate sensitivity for linear bipolar devices and ICs. Effects of preirradiation elevated temperature stress on MOS radiation response are also a significant concern. Trends are identified for future radiation hardness tests on advanced microelectronics technologies.

Use of COTS microelectronics in radiation environments

This paper addresses key issues for the cost-effective use of COTS (Commercially available Off The Shelf) microelectronics in radiation environments that enable circuit or system designers to manage risks and ensure mission success. We review several factors and tradeoffs affecting the successful application of COTS parts including (1) hardness assurance and qualification issues; (2) system hardening techniques, and (3) life-cycle costs. The paper also describes several experimental studies that address trends in total-dose, transient, and single-event radiation hardness as COTS technology scales to smaller feature sizes. As an example, the level at which dose-rate upset occurs in Samsung SRAMs increases from 1.4/spl times/10/sup 8/ rad(Si)/s for a 256 K SRAM to 7.7/spl times/10/sup 9/ rad(Si)/s for a 4 M SRAM, indicating unintentional hardening improvements in the design or process of a commercial technology. Additional experiments were performed to quantify variations in radiation hardness for COTS parts. In one study, only small (10-15%) variations were found in the dose-rate upset and latchup thresholds for Samsung 4 M SRAMs from three different date codes. In another study, irradiations of 4 M SRAMs from Samsung, Hitachi, and Toshiba indicate large differences in total-dose radiation hardness. The paper attempts to carefully define terms and clear up misunderstandings about the definitions of "COTS" and "radiation-hardened (RH)" technology.

Challenges in hardening technologies using shallow-trench isolation

Challenges related to radiation hardening CMOS technologies with shallow-trench isolation are explored. It is shown that developing a radiation-hardened CMOS technology with shallow trench isolation is more complex than using a traditional hardened field oxide as the trench insulator. We illustrate the use of device simulations in concert with measurements on test structures to provide detailed physical insight into methods for improving total-dose radiation response. Mechanisms that can limit the total-dose radiation hardness of shallow trench isolation such as high electric fields and ion implantation damage are explored. We demonstrate the successful conversion of a non-radiation hardened technology with LOCOS isolation (Sandia's CMOS6) into a greater than 1 Mrad(SiO/sub 2/) radiation-hardened shallow-trench isolated technology (Sandia's CMOS6r).

Electrical properties and radiation hardness of SOI systems with multilayer buried dielectric

In this work SOI structures with buried SiO/sub 2/-Si/sub 3/N/sub 4/-SiO/sub 2/ layers have been fabricated by the ZMR-technique with the aim of improving the total dose radiation hardness of the buried dielectric layer. To optimize the fabrication process, buried layers were investigated by secondary ion mass spectrometry before and after the ZMR process, and the obtained results were compared with electrical measurements. It is shown that optimization of the preparation processes of the initial buried dielectric layers provides ZMR SOI structures with multilayer buried isolation, which are of high quality for both Si film interfaces. Particular attention is paid to the investigation of radiation-induced charge trapping in buried insulators. Buried isolation structures with a nitride layer exhibit significant reduction of radiation-induced positive charge as compared to classical buried SiO/sub 2/ layers produced by either the ZMR or the SIMOX technique.