Radiation-induced Leakage Current Research Articles

Characterisation of gamma-irradiated MCz-silicon detectors with a high-K negative oxide as field insulator

Abstract The high-luminosity operation of the Tracker in the Compact Muon Solenid (CMS) detector at the Large Hadron Collider (LHC) experiment calls for the development of silicon-based sensors. This involves implementation of AC-coupling to micro-scale pixel sensor areas to provide enhanced isolation of radiation-induced leakage currents. The motivation of this study is the development of AC-pixel sensors with negative oxides (such as aluminium oxide — Al2O3 and hafnium oxide — HfO2) as field insulators that possess good dielectric strength and provide radiation hardness. Thin films of Al2O3 and HfO2 grown by atomic layer deposition (ALD) method were used as dielectrics for capacitive coupling. A comparison study based on dielectric material used in MOS capacitors indicate HfO2 as a better candidate since it provides higher sensitivity (where, the term sensitivity is defined as the ratio of the change in flat-band voltage to dose) to negative charge accumulation with gamma irradiation. Further, space charge sign inversion was observed for sensors processed on high resistivity p-type Magnetic Czochralski silicon (MCz-Si) substrates that were irradiated with gamma rays up to a dose of 1 MGy. The inter-pixel resistance values of heavily gamma irradiated AC-coupled pixel sensors suggest that high-K negative oxides as field insulators provide a good electrical isolation between the pixels.

A Novel S-Gate-Assisted SOI n-MOSFET for Total Ionizing Dose Radiation Reinforcement

In this article, a novel S-gate-assisted silicon-on-insulator n-channel metal–oxide–semiconductor field-effect transistor (SGA SOI n-MOSFET) structure is proposed in order to suppress the total ionizing dose (TID) effect. The new structure settles the radiation-induced leakage current by isolating both the source and drain from the shallow trench isolation (STI) oxides and introducing two auxiliary gates. This work simulates the TID irradiation of three SOI n-MOSFET devices by Sentaurus TCAD and verifies the anti-TID irradiation characteristics of the proposed SGA SOI n-MOSFET. After the novel SGA SOI n-MOSFET was irradiated with 500 krad(Si), the OFF-state leakage current is only marginally increased, the ON-state leakage current is almost unchanged, the threshold voltage drift is 9.423%, and the transconductance degradation is only 7.453%. The simulation results demonstrated the proposed SGA SOI n-MOSFET resisted TID radiation doses up to 500 krad(Si). Meanwhile, the SGA SOI n-MOSFET is much more compact and saves tremendous cost compared with the H-gate-assisted (HGA) SOI n-MOSFET during very large scale integration (VLSI) fabrication and mass production. Moreover, the SGA SOI n-MOSFET solves the disadvantages of the ring-gate-assisted (RGA) SOI n-MOSFET complex aspect ratio <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${W}/{L}$ </tex-math></inline-formula> design. The SGA SOI n-MOSFET offers a better alternative for nonultrahigh radiation dose environments.

Characterization of Heavily Irradiated Dielectrics for Pixel Sensors Coupling Insulator Applications

An increase in the radiation levels during the high-luminosity operation of the Large Hadron Collider calls for the development of silicon-based pixel detectors that are used for particle tracking and vertex reconstruction. Unlike the conventionally used conductively coupled (DC-coupled) detectors that are prone to an increment in leakage currents due to radiation, capacitively coupled (AC-coupled) detectors are anticipated to be in operation in future collider experiments suitable for tracking purposes. The implementation of AC-coupling to micro-scale pixel sensor areas enables one to provide an enhanced isolation of radiation-induced leakage currents. The motivation of this study is the development of new generation capacitively coupled (AC-coupled) pixel sensors with coupling insulators having good dielectric strength and radiation hardness simultaneously. The AC-coupling insulator thin films were aluminum oxide (Al2O3) and hafnium oxide (HfO2) grown by the atomic layer deposition (ALD) method. A comparison study was performed based on the dielectric material used in MOS, MOSFET, and AC-coupled pixel prototypes processed on high resistivity p-type Magnetic Czochralski silicon (MCz-Si) substrates. Post-irradiation studies with 10 MeV protons up to a fluence of 1015 protons/cm2 suggest HfO2 to be a better candidate as it provides higher sensitivity with negative charge accumulation on irradiation. Furthermore, even though the nature of the dielectric does not affect the electric field within the AC-coupled pixel sensor, samples with HfO2 are comparatively less susceptible to undergo an early breakdown due to irradiation. Edge-transient current technique (e-TCT) measurements show a prominent double-junction effect as expected in heavily irradiated p-type detectors, in accordance with the simulation studies.

L Style n-MOSFET Layout For Mitigating TID Effects

This paper proposes a new rad hard layout L style of nmos metal oxide semiconductor field effect transistor (n-MOSFET), which is evaluated to show that its efficacy at reducing radiation-induced leakage currents, thus improving the total ionization dose(TID) tolerance with very less area and parasitic capacitance as compared to enclosed layout transistor(ELT). This proposed layout structure is fully compatible to present commercial fabrication technology without any additional mask requirement as compared to conventional n MOSFET fabrication and can be used as radiation tolerant by design technique. The simulated ID - VG characteristics of the rad hard L n-MOSFET layout demonstrated the effectiveness of eliminating radiation-induced leakage current paths. The leakage current in proposed rad hard L n-MOSFET has been reduced by factor of 108 at 300Krad dose as compared to conventional layout n-MOSFET.

Total-Ionizing-Dose Radiation-Induced Dual-Channel Leakage Current at Unclosed Edge Termination for High Voltage SOI LDMOS

Total-ionizing-dose (TID) radiation response on unclosed edge termination is investigated for high voltage silicon-on-insulator (SOI) laterally diffused metal-oxide-semiconductor (LDMOS) in this article. Radiation-induced dual-channel leakage current model is proposed to reveal the mechanism of leakage current generation at OFF-state. Radiation causes a mass of positive oxide trapped charges generated in field oxide (FOX) layer and buried oxide layer. Owing to the P-SOI layer with significantly low doping concentration, two inversion channels are formed at the surface and bottom in the edge termination region, which provides parallel conduction paths. Electrons from the source N+ are pulled down and flow along the bottom channel while punchthrough occurring. The radiation-induced leakage current could be suppressed by thinning FOX layer, increasing the doping concentration of the P-SOI layer, and thickening the SOI layer.

New Radiation-Hardened Design of a CMOS Instrumentation Amplifier and its Tolerant Characteristic Analysis

A radiation-hardened instrumentation amplifier (IA) that allows precise measurement in radiation environments, including nuclear power plants, space environments, and radiation therapy rooms, was designed and manufactured, and its characteristics were verified. Most electronic systems are currently designed using silicon-based complementary metal-oxide semiconductor (CMOS) integrated circuits (ICs) to achieve a highly integrated low-power design. However, fixed charges induced in silicon by ionization radiation cause various negative effects, resulting in, for example, the generation of leakage current in circuits, performance degradation, and malfunction. Given that such problems in radiation environments may directly lead to a loss of life or environmental contamination, it is critical to implement radiation-hardened CMOS IC technology. In this study, an IA used to amplify fine signals of the sensors was designed and fabricated in the 0.18 μm CMOS bulk process. The IA contained sub-circuits that ensured the stable voltage supply needed to implement system-on-chip (SoC) solutions. It was also equipped with special radiation-hardening technology by applying an I-gate n-MOSFET that blocks the radiation-induced leakage currents. Its ICs were verified to provide the intended performance following a total cumulative dose of up to 25 kGy(Si), ensuring its safety in radiation environments.

Observation of Radiation-Induced Leakage Current Defects in MOS Oxides With Multifrequency Electrically Detected Magnetic Resonance and Near-Zero-Field Magnetoresistance

We report high and low-frequency electrically detected magnetic resonance measurements and near-zero-field magnetoresistance measurements on radiation-induced leakage currents in irradiated Si/SiO2 metal-oxide-silicon (MOS) structures. This study identifies the chemical and physical nature of atomic-scale defects involved in radiation-induced leakage currents in SiO2 using an analytical technique. Our results suggest that trap-assisted tunneling through these Si/SiO2 structures involves Pb centers (silicon dangling bonds at the Si/SiO2 interface), rather than only ${E}$ ’ centers (oxygen vacancies in the SiO2 film). We utilize simulations of the defects’ resonance spectra to provide further evidence for the involvement of interface Pb centers in the radiation-induced leakage currents. These simulations also explore the possibility of additional ${E}$ ’ center involvement in the radiation-induced leakage currents.

Total-Ionizing-Dose Effects and Low-Frequency Noise in 30-nm Gate-Length Bulk and SOI FinFETs With SiO2/HfO2Gate Dielectrics

Total-ionizing-dose (TID) effects and low-frequency noise are evaluated in 30-nm gate-length bulk and silicon-on-insulator (SOI) FinFETs for devices with fin widths of 10–40 nm. Minimal threshold voltage shifts are observed at 2 Mrad(SiO2), but large increases in low-frequency noise are found, and significant changes in defect-energy distributions are inferred. Radiation-induced leakage current is enhanced for narrow- and short-channel bulk FinFETs. Short-channel SOI FinFETs show enhanced degradation compared with longer-channel devices. Narrow- and short-channel SOI devices exhibit high radiation tolerance. Significant random telegraph noise (RTN) is observed in smaller devices due to prominent individual defects.

Investigating the latent reliability degradation of partially depleted SOI devices induced by high-energy heavy ions irradiation

Through electrical stress and annealing experiments performed on irradiated partially depleted SOI MOS devices, high-energy heavy ions induced defects in the gate oxide are shown to affect insulation character and the long time reliability of the devices. A decrease of the time-dependent dielectric breakdown (TDDB) lifetime and an increase of the radiation-induced leakage current (RILC) were observed after irradiation at the nominal operating irradiation bias. But then, the RILC was completely removable using isochronal annealing experiment, while the TDDB lifetime did not increase back to its initial value. We interpreted these results and degeneration mechanisms in terms of the neutral electrons traps and morphological oxide defects induced by high-energy heavy ions, which may be meaningful to evaluate the reliability of the devices used in the radiation environment.

The CMS ECAL Phase-2 upgrade for high precision energy and timing measurements

The CMS electromagnetic calorimeter (ECAL) is a homogeneous calorimeter made of about 75,000 lead tungstate scintillating crystals. In view of the high-luminosity phase of the LHC, the ECAL electronics must be upgraded to cope with the more stringent requirements in terms of trigger latency and rate. The new electronics will transmit the data in streaming mode from the front-end electronics to the off-detector electronics, where the trigger primitives will be formed in powerful FPGAs. The front-end electronics will feature two new radiation-hard chips: a dual gain trans-impedance amplifier (TIA) and a sampling ADC with loss-less data compression. The TIA choice preserves the fast pulse shape of signals in the lead tungstate coupled to avalanche photodiodes (APD), and it is more resilient to the noise increase due to the radiation-induced APD leakage current. An important characteristic of the new design will be the capability to provide precision timing measurements, of the order of 30ps, for photons and electrons above 50GeV. The excellent time resolution will improve the overall CMS physics performance by mitigating the high pile-up effects. First characterization results of the TIA chip will be shown, and studies of energy and timing resolution performed in beam tests with the prototype electronics will be presented.

Research for radiation-hardened high-voltage SOI LDMOS

Based on the silicon-on-insulator (SOI) technology and radiation-hardened silicon gate (RSG) process, a radiation-hardened high-voltage lateral double-diffused MOSFET (LDMOS) device is presented in this paper. With the gate supply voltage of 30 V, the LDMOS device has a gate oxide thickness of 120 nm, and the RSG process is effective in reducing the total ionizing dose (TID) radiation-induced threshold voltage shift. The p-type ion implantation process and gate-enclosed layout topology are used to prevent radiation-induced leakage current through a parasitic path under the bird's beak and at the deep trench corner, and the device is compatible with high-voltage SOI CMOS process. In the proposed LDMOS, the total ionizing dose radiation degradation for the ON bias is more sensitive than the OFF bias. The experiment results show that the SOI LDMOS has a negative threshold voltage shift of 1.12 V, breakdown voltage of 135 V, and off-state leakage current of 0.92 pA/μm at an accumulated dose level of 100 krad (Si).

Quasi-3D TCAD modeling of STI radiation-induced leakage currents in SOI MOSFET structure

Quasi-3D model for calculation of radiation leakage currents in modern submicron Silicon-on-Insulator (SOI) metal–oxide–semiconductor field-effect transistor (MOSFET) structures is proposed. The solution of a complex 3-dimensional problem is reduced to solving two tasks: 2D modeling of the traditional MOSFET cross-section and 3D modeling of the side parasitic transistor. The radiation-induced leakage current simulation in the 0.35 μm SOI MOSFET structure with taking account ionizing radiation with a dose of up to 500 krad was simulated. The results of the simulation show that in comparison with the traditional fully 3D modeling, which requires 11 hours of computer time, the computer time for the IdVg characteristic was reduced to 71 minutes (i.e. the computer time decreased by 9 times).

Radiation-tolerance analysis of I-gate n-MOSFET according to isolation oxide module in the CMOS bulk process

The n-type metal-oxide-semiconductor field-effect transistor (n-MOSFET) produced in the widely used CMOS bulk process takes radiation damage by the total ionizing dose (TID) effects in radiation environments, so the radiation-tolerant properties of semiconductor integrated-circuits (ICs) used in high-radiation environments is a critical issue. The formation method of the isolation oxide module (IOM), which induces the radiation-induced leakage currents, differs depending on the chip density of the CMOS bulk process. In this paper, we designed and fabricated I-gate n-MOSFETs for bulk process and analyzed the radiation-tolerant characteristics according to IOM. The I-gate n-MOSFET chips are fabricated using the shallow trench isolation (STI) 0.18um and local oxidation of silicon (LOCOS) 0.35um processes of the CMOS bulk process. Tests and evaluation of the TID effects on the chips are carried out by irradiating a total cumulative dose up to 2 Mrad(Si). As the results, in the standard n-MOSFET, the leakage currents of the LOCOS and STI processes are 27.7uA and 16.4uA, and in I-gate n-MOSEFT, are 1.1uA and 0.7uA. The leakage currents of standard n-MOSFET increased by about 25 times before and after irradiation, but the electric characteristics of I-gate n-MOSFET is maintained regardless of the process. Therefore, the process versatility of the I-gate n-MOSFET with the radiation-tolerant performance has been verified.

Heavy ion induced upset errors in 90-nm 64 Mb NOR-type floating-gate Flash memory**Project supported by the National Natural Science Foundation of China (Grant No. 616340084), the Youth Innovation Promotion Association of CAS (Grant No. 2014101), the International Cooperation Project of CAS, and the Austrian-Chinese Cooperative R&D Projects (Grant No. 172511KYSB20150006).

Upset errors in 90-nm 64 Mb NOR-type floating-gate Flash memory induced by accelerated 129Xe and 209Bi ions are investigated in detail. The linear energy transfer covers the range from 50 to 99.8 MeV/(mg/cm2). When the memory chips are powered off during heavy ions irradiation, single-event-latch-up and single-event-function-interruption are excluded, and only 0->1 upset errors in the memory array are observed. These error bit rates seem very difficult to achieve and cannot be simply recovered based on the power cycle. The number of error bits shows a strong dependence on the linear energy transfer (LET). Under room-temperature annealing conditions, the upset errors can be reduced by about two orders of magnitude using rewrite/reprogram operations, but they subsequently increase once again in a few minutes after the power cycle. High-temperature annealing can diminish almost all error bits, which are affected by the lower LET 129Xe ions. The percolation path between the floating-gate (FG) and the substrate contributes to the radiation-induced leakage current, and has been identified as the root cause of the upset errors of the Flash memory array in this work.

Enhanced radiation-induced narrow channel effects in 0.13- PDSOI nMOSFETs with shallow trench isolation**Project supported by the Weapon Equipment Pre-Research Foundation of China (Grant No. 9140A11020114ZK34147) and the Shanghai Municipal Natural Science Foundation, China (Grant No. 15ZR1447100).

Total ionizing dose responses of different transistor geometries after being irradiated by 60Co γ-rays, in 0.13- partially-depleted silicon-on-insulator (PD SOI) technology are investigated. The negative threshold voltage shift in an n-type metal-oxide semiconductor field effect transistor (nMOSFET) is inversely proportional to the channel width due to radiation-induced charges trapped in trench oxide, which is called the radiation-induced narrow channel effect (RINCE). The analysis based on a charge sharing model and three-dimensional technology computer aided design (TCAD) simulations demonstrate that phenomenon. The radiation-induced leakage currents under different drain biases are also discussed in detail.

Investigating the TDDB lifetime growth mechanism caused by proton irradiation in partially depleted SOI devices

We have investigated the effects of proton irradiation on the subsequent time-dependent dielectric breakdown (TDDB) lifetimes of partially depleted (PD) SOI devices. Our results show that the TDDB lifetimes of the devices increased after proton irradiation and the amplitude increased with the intensification of the total ionizing dose (TID) damage. Moreover, the radiation-induced leakage currents (RILC) and the TDDB lifetimes of the irradiated devices by protons were dependent on TID damage but independent of energy of protons. We interpreted these results and mechanisms in terms of the effects of radiation-induced traps on the stressing current during the reliability testing, which may be significant to further expand the understanding of the radiation effects of the devices used in the space radiation environment.

Effects of Channel Implant Variation on Radiation-Induced Edge Leakage Currents in n-Channel MOSFETs

The effects of radiation-induced defects and statistical variation in the dose and energy of MOSFET channel implants in a modern bulk CMOS technology are modeled using a process simulator in combination with analytical computations. The model integrates doping profiles obtained from process simulations and experimentally determined defect potentials into implicit surface potential equations. Solutions to these equations are used to model radiation-induced edge leakage currents in 90-nm bulk CMOS n-channel MOSFETs. The results indicate that slight variations in the channel implant parameters can have a significant impact on the doping profile along the shallow trench isolation sidewall and thus the radiation-induced edge leakage currents.

Total Ionizing Dose Effects on a 12-bit 40kS/s SAR ADC Designed With a Dummy Gate-Assisted n-MOSFET

A 12-bit 40kS/s successive approximation register analog-to-digital converter (ADC) designed with a dummy gate-assisted (DGA) n-MOSFET is presented for space applications requiring high resolution, low power consumption, and moderate conversion speed. Additionally, a custom-designed metal finger capacitor and a body-tied p-MOSFET protected by guard ring in a bootstrapping circuit were used to mitigate the performance degradation caused by radiation-induced leakage current. The designed ADC was fabricated in a commercial standard 0.35 $\mu {\mathrm { m}}$ CMOS process. In order to evaluate its radiation hardness, the fabricated ADC was exposed to 60Co gamma rays with a dose of up to 300krad (Si). The measured signal-to-noise-and-distortion ratio (SNDR) and spurious-free dynamic range (SFDR) were 67.9dB and 78.7dB, respectively. Although a small amount of degradation of the SNDR was observed after radiation exposure, it corresponds to only about a 0.1 effective-number-of-bit (ENOB) drop from the measured result of an unirradiated chip.

Influence of the Total Ionizing Dose Irradiation on 130 nm Floating-body PDSOI NMOSFETs

This paper investigates the impact of ionizing radiation on floating body effects for the 130 nm PDSOI NMOSFETs. It is shown that the floating body effects are restrained by the irradiation both for the core device and the input/output (I/O) device. For the core device, the second peak of the front gate transconductance which is known as the gate-induced floating body effect degrades with the incremental total dose. The decline of the second g <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> peak is ascribed to the impact of the radiation-induced leakage current, but not to the radiation-induced interface traps assisted recombination or the suppression of the electron valence band (EVB) tunneling. For the I/O device, the kink effect and the hysteresis effect in the output characteristic which are observed before irradiation become insignificant after irradiation. These phenomena are due to the fully depleted of the silicon film in the I/O device which is caused by the buried oxide charge trapping. In addition, a radiation-induced latch, which is result from the leakage current-induced impact ionization, is also observed in the I/O device.

Failure of the negative voltage regulator in medium-photon-energy X radiation fields

Negative voltage regulators were examined in the effective 60-keV and 170-keV bremsstrahlung fields, as well as in the field of 60Co gamma-radiation. Most devices irradiated in the fields of medium-dose-rate breaking radiation failed to operate after absorption of very small total doses of ionizing radiation, in the range of 37–132Gy(SiO2). However, all samples irradiated in the gamma radiation environment remained completely functional, even after deposition of a total dose of 500Gy(SiO2). Devices irradiated with higher input voltages failed after absorption of low total doses, whereas the load current increase mitigated and even prevented circuit failures in X radiation fields. The high radiation sensitivity of the LM2990T-5 voltage regulators operating in the bremsstrahlung fields was a consequence of the dose enhancement on the gold–aluminum connection between the silicon chip and ground contact. Computer model simulations indicated that the primary failure mechanisms were the generation of radiation-induced leakage currents alongside the npn transistors in the operational amplifier circuit. The difference between the voltage regulator responses in various bremsstrahlung environments was affected by the time-dependent effects, leading to the partial recovery of radiation-induced trapped charge.