Modeling of the tunneling current in MOS devices after proton irradiation using a nonlinear series resistance correction

Contrary to what is expected for a damaged device, the impact of 10 MeV-energy protons on a metal-oxide-semiconductor (MOS) structure can give rise to a significant reduction of the gate tunneling current, mainly in the high bias range. In order to simulate the observed deviation, a correction to the oxide field in the Fowler-Nordheim tunneling expression is considered. Since the nature and location of the device damaged region have not been clearly identified yet, the conduction problem is circumvented by introducing an effective nonlinear series resistance correction. Experimental and simulated data obtained as a function of the irradiation fluences supporting the proposed approach are presented. The possible origin of this nonlinear resistance and its implications for the reliability assessment of irradiated MOS devices are also discussed.Fil: Palumbo, Félix Roberto Mario. Comisión Nacional de Energía Atómica. Gerencia del Área de Investigaciones y Aplicaciones no Nucleares. Gerencia de Física (Centro Atómico Constituyentes); Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Miranda, Enrique. Universitat Autònoma de Barcelona; Españ

Radiation Effects in CMOS Isolation Oxides: Differences and Similarities With Thermal Oxides

Radiation effects in thick isolation oxides of modern CMOS technologies are investigated using dedicated test structures designed using two commercial foundries. Shallow Trench Isolation and Pre-Metal Dielectric are studied using electrical measurements performed after X-ray irradiations and isochronal annealing cycles. This paper shows that trapping properties of such isolation oxides can strongly differ from those of traditional thermal oxides usually used to process the gate oxide of Metal Oxide Semiconductor Field Effect Transistors. Buildup and annealing of both radiation-induced oxide-trap charge and radiation-induced interface traps are discussed as a function of the oxide type, foundry and bias condition during irradiation. Radiation-induced interface traps in such isolation oxides are shown to anneal below 100°C contrary to what is usually observed in thermal oxides. Implications for design hardening and radiation tests of CMOS Integrated Circuits are discussed

Gamma and proton irradiation effects and thermal stability of electrical characteristics of metal-oxide-silicon capacitors with atomic layer deposited Al<inf>2</inf>O<inf>3</inf> dielectric

The radiation hardness and thermal stability of the electrical characteristics of atomic layer deposited Al2O3 layers to be used as passivation films for silicon radiation detectors with slim edges are investigated. To directly measure the interface charge and to evaluate its change with the ionizing dose, metal-oxide-silicon (MOS) capacitors implementing differently processed Al2O3 layers were fabricated on p-type silicon substrates. Qualitatively similar results are obtained for degradation of capacitance-voltage and current-voltage characteristics under gamma and proton irradiations up to equivalent doses of 30 Mrad and 21.07 Mrad, respectively. While similar negative charge densities are initially extracted for all non-irradiated capacitors, superior radiation hardness is obtained for MOS structures with alumina layers grown with H2O instead of O3 as oxidant precursor. Competing effects between radiation-induced positive charge trapping and hydrogen release from the H2O-grown Al2O3 layers may explain their higher radiation resistance. Finally, irradiated and non-irradiated MOS capacitors with differently processed Al2O3 layers have been subjected to thermal treatments in air at temperatures ranging between 100 °C and 200 °C and the thermal stability of their electrical characteristics has been evaluated. Partial recovery of the gamma-induced degradation has been noticed for O3-grown MOS structures. This can be explained by a trapped holes emission process, for which an activation energy of 1.38 ± 0.15 eV has been extracted.Peer reviewe

Ionizing radiation e\ufb00ects in nanoscale CMOS technologies exposed to ultra-high doses

This thesis studies the e\ufb00ects of radiation in nanoscale CMOS technologies exposed to ultra-high total ionizing doses (TID), up to 1 Grad(SiO2). These extreme radiation levels are orders of magnitude higher that those typically experienced by space applications (where radiation e\ufb00ects in electronic are of concern). However, they can be found in some speci\ufb01c applications like the large-hadron-collider (LHC) of CERN, and, in particular, in its future upgrade, the high-luminosity LHC (HL-LHC). The study at such high doses has both revealed new phenomena, and has contributed to a better understanding of some of the already known radiation-induced e\ufb00ects. The radiation response of four di\ufb00erent CMOS technology nodes, i.e., 130, 65, 40 and 28 nm, coming from di\ufb00erent manufacturers, has been investigated in di\ufb00erent conditions of temperature, bias, dose-rate and for di\ufb00erent transistor\u2019s sizes, providing an unique and comprehensive set of data about the ultra-high TID-induced phenomena in modern CMOS technologies. This study has con\ufb01rmed that the thin gate oxide of nanoscale technologies is extremely robust to radiation, even at ultra-high doses. The main cause of performance degradation has been identi\ufb01ed in the presence of auxiliary oxides such as shallow trench insulation oxides (STI) and spacers. Both radiation-induced drain-to-source leakage current increase and radiation-induced narrow channel e\ufb00ect (RINCE) are caused by positive charge trapped in the STI. In this work, thanks to exposures to very high TID levels and to measurements performed in di\ufb00erent conditions of temperature and bias, we show that the two e\ufb00ects are provoked by charge trapped in di\ufb00erent locations along the trench oxide. Moreover, a new unexpected ultra-high-dose drain current increase (UCLI) e\ufb00ect, a\ufb00ecting narrow and long nMOS transistors, has been observed. In-depth studies of the radiation-induced short channel e\ufb00ect (RISCE), related to the presence of the spacers, have shown that, at ultra-high doses, the degradation mechanism consists of two phases. A \ufb01rst increase of the series resistance, caused by the radiation-induced charge trapping in the spacers, is followed by a threshold voltage shift provoked by the transport of hydrogen ions from the spacers to the gate oxide. This model has been validated by several static measurements, TCAD simulations and charge pumping measurements. The dependencies of these e\ufb00ects on bias, temperature and size of the transistors have also been studied in detail. Moreover, an unexpected true dose-rate sensitivity has been measured in both nMOS and pMOS transistors in 65 and 130 nm technologies, although the radiation response of MOS devices is considered insensitive to true dose-rate e\ufb00ects. The current degradation in samples irradiated at a dose-rate comparable to that expected in the HL-LHC is larger by a factor of 3c2 than that measured in the typical quali\ufb01cation test, usually carried out with a much higher dose-rate. This is clearly of serious concern for the quali\ufb01cation of circuits designed for the particle detectors of the HL-LHC

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 10(15) protons/cm(2) 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.Peer reviewe

Proton Damage Effects on Carbon Nanotube Field-Effect Transistors

This research investigated the effects of proton damage on single-walled carbon nanotube (SWCNT) transistors. The transistors were irradiated by 1.8 MeV protons to determine the damage induced in the SWCNTs and the device substrate using Raman spectroscopy, and to observe the effect on transistor functionality by measuring current-voltage characteristics. Irradiation of the SWCNT transistors to a fluence of 1x1013 protons/cm2 resulted in 67% increase in the Raman D/G peak intensity ratio, while at a fluence of 2x1013 protons/cm2 the increase in the D/G ratio was only 18%, likely due to radiation annealing. Current-voltage measurements indicated an increasingly negative threshold voltage shift in SWCNT transistors as a function of proton fluence: -1.3 V after a fluence of 1x1012 protons/cm2 and -1.9 V after a fluence of 2x1013 protons/cm2. The drain current decreased 33% after a fluence of 1x1012 protons/cm2 and 58% after a fluence of 2x1013 protons/cm2. Charge pumping of the SWCNT transistors revealed a significant error attributed to the combination of the non-uniform distribution of SWCNTs across the gate region, adsorbates on the exposed SWCNT and gate oxide surfaces, and inconsistency in transistor performance. The transistor hysteresis also increased as a function of the proton fluence due to interface and bulk charge trapping. This research provided insight into the effect on SWCNT transistors due to proton irradiations up to a fluence of 2x1013 protons/cm2 demonstrating both interface and bulk damage effects

대면적 단분자층 이황화 몰리브덴 박막 합성 및 전계효과 트랜지스터에의 응용

학위논문 (박사)-- 서울대학교 대학원 자연과학대학 물리·천문학부, 2017. 8. 이탁희.Two-dimensional (2D) transition-metal dichalcogenides (TMDCs) have gained considerable attention as an emerging semiconductor due to their promising atomically thin film characteristics with good field-effect mobility and a tunable bandgap energy. Among TMDC materials, molybdenum disulfide (MoS2) has gained significant attention due to its direct bandgap of 1.8 eV as a single layer. Herein, numerous studies have explored the application of MoS2 in nanoelectronic devices. To make full use of its unique optical and electrical merits in practical applications, however, synthesis of large and uniform monolayer MoS2 is highly necessary. In this regard, a chemical vapor deposition (CVD) technique has been intensively used to produce large and uniform monolayer MoS2. Meanwhile, their electronic applications have been generally realized with conventional inorganic electrodes and dielectrics implemented using conventional photolithography or transferring processes that are not compatible with large-area and flexible device applications. To facilitate the advantages of 2D TMDCs in practical applications, novel strategies for realizing flexible and transparent 2D electronics using low-temperature, large-area, and low-cost processes should be developed. Here, in this dissertation, the study on the atomically thin MoS2 synthesis and its application to FETs will be discussed. First, the effect of irradiation on MoS2 FETs with 10 MeV high energy proton beams will be discussed. The electrical characteristics of the devices were measured before and after proton irradiation with different fluence conditions. The electrical changes were explained by the proton-irradiation-induced traps, including positive oxide-charge traps in the SiO2 layer and trap states at the interface between the MoS2 channel and the SiO2 layer. Second, the CVD synthesis of large and monolayer MoS2 film will be discussed. The predominantly monolayer character of the CVD-grown MoS2 film was verified by atomic force microscopy (AFM), Raman, and photoluminescence (PL) spectroscopy measurements. Third, the electrical properties of synthesized large-area monolayer MoS2 field-effect transistors with low-cost inkjet-printed Ag electrodes will be discussed. The monolayer MoS2 film was grown by CVD method, and the top-contact Ag source/drain electrodes (S/D) were deposited onto the films using a low-cost drop-on-demand inkjet-printing process without any masks and surface treatments. The electrical characteristics of FETs were comparable to those fabricated by conventional deposition methods such as photo or electron beam lithography. Last, the fully printed transparent CVD-synthesized monolayer MoS2 phototransistor arrays on flexible polymer substrates will be discussed. All the electronic components, including dielectric and electrodes, were directly deposited with mechanically tolerable organic materials by inkjet-printing technology onto transferred monolayer MoS2. By integrating the soft organic components with ultra-thin MoS2, the fully printed MoS2 phototransistors exhibits excellent transparency and mechanically stable operation.1. Introduction 1 1.1. Graphene and 2D materials 1 1.2. Molybdenum disulfide (MoS2) 1 References 2 2. Proton beam irradiation effect on atomically thin MoS2 field-effect transistors 3 2.1. Introduction 3 2.2. Experiments 4 2.2.1. Device fabrication process 4 2.2.2. Proton beam irradiation experiment 6 2.2.3. Electrical characteristics measurements 6 2.3. Results and discussions 6 2.3.1. Electrical characteristics 6 2.3.2. Dose-dependence and Raman spectra 9 2.3.3. Time-dependence 11 2.3.4. Stopping and Range of Ions in Matter 12 2.3.5. Energy band diagram 14 2.4. Conclusion 15 References 16 3. Chemical vapor deposition of monolayer MoS2 film 20 3.1. Introduction 20 3.1.1. Limit of mechanical exfoliation 20 3.1.2. Many synthesis methods 20 3.2. CVD system setup . 21 3.3. Material characterization 22 3.3.1. Atomic force microscopy 22 3.3.2. Raman and photoluminescence 23 3.3.3. Electrical characteristics of triangular islands 24 3.4. Conclusion 25 References 26 4. Inkjet-printed contact electrodes on CVD-synthesized MoS2 film 29 4.1. Introduction 29 4.2. Experiments 31 4.2.1. Inkjet-printing process 32 4.3. Results and discussions 32 4.3.1. Electrical characteristics 32 4.3.2. Y-function method and contact resistances 33 4.3.3. Electrical instability and gate-bias stress effect 35 4.4. Conclusion 37 References 38 5. Fully flexible and transparent MoS2 phototransistor with inkjet-printed components 43 5.1. Introduction 43 5.2. Experiments 44 5.2.1. Device fabrication process 44 5.2.2. Light illumination setup 45 5.2.3. Optical transmittance of the device 47 5.3. Results and discussions 48 5.3.1. Fully-printed MoS2 phototransistors 48 5.3.2. Characteristics of CVD-grown monolayer MoS2 film 49 5.3.3. Electrical characteristics under bent conditions 52 5.3.4. Photo-characteristics 53 5.4. Conclusion 56 References 57 6. Summary 60 Abstract (In Korean) 61 Curriculum Vitae 63Docto

Electrical correlation of double-diffused metaloxidesemiconductor transistors exposed to gamma photons, protons, and hot carriers

Double-diffused metaloxidesemiconductor n-channel power transistor devices were subjected to a high electric-field stress, gamma photons 60Co, and 10-MeV proton radiation, and were comparatively analyzed. The direct-current currentvoltage and high-frequency capacitancevoltage techniques were used to characterize the two different regions under the gate oxide in this kind of devices. The SiSiO2 interfaces at the channel side and at the drain side are characterized after thermal annealing. The correlation of the interface states with the trapped charge is a good quantitative tool to compare the effects from different degradation mechanisms. It is shown that, under given conditions, each kind of stress exhibits its own signature in the interface states versus the oxide charge plot.Fil: Palumbo, Félix Roberto Mario. Comisión Nacional de Energía Atómica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Faigon, Adrián Néstor. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires; ArgentinaFil: Curro, Giuseppe. No especifíca

2 MeV electron irradiation effects on the electrical characteristics of metal-oxide-silicon capacitors with atomic layer deposited Al<inf>2</inf>O <inf>3</inf>, HfO<inf>2</inf> and nanolaminated dielectrics

The effects of 2 MeV electron irradiation on the electrical characteristics of atomic layer deposited (ALD) high permittivity (high-k) layers of Al 2O3, HfO2 and a nanolaminate of them are evaluated. Metal-oxide-semiconductor capacitors with a nominal dielectric physical thickness of 10 nm were fabricated on different p-type and n-type silicon substrates. The capacitance-voltage (C-V) and current-voltage (I-V) characteristics of the different structures are analyzed as a function of electron irradiation. A progressive negative shift of the C-V characteristics is observed with increasing electron irradiation, indicating the generation of effective positive charges. Similar generation rates for effective trapped charges and interface states are obtained for all the different high-k dielectric layers studied. The hysteresis of the C-V curves after irradiation increases in the case of Al2O3 samples, for HfO 2 decreases while the irradiation has little impact on the hysteresis of the nanolaminate stack. A progressive increase of the leakage current with electron irradiation dose is observed for all the studied dielectrics. The analysis of the current-voltage characteristics measured at different temperatures point to Poole-Frenkel as the dominant conduction mechanism. Under the studied conditions, no impact of electron irradiation fluence on dielectric breakdown voltage has been appreciated. © 2012 Elsevier Ltd. All rights reserved.Peer reviewe