Total Ionizing Dose Response of High-k Dielectrics on MOS Devices

As advanced Metal Oxide Semiconductor Field Effect Transistors (MOSFETs) technology continues to minimize the gate oxide thickness, the exponential increase in gate leakage current poses a major challenge for silicon dioxide (SiO2) based devices. In order to reduce the gate leakage current while maintaining the same gate capacitance, alternative gate insulator materials with higher dielectric constant (high-k) became the preferred replacement of SiO2 gate dielectrics. Germanium (Ge) MOSFETs have been regarded as promising candidates for future high-speed applications because they possess higher carrier mobility when compared to silicon based devices. At present, advanced microelectronics devices and circuits are used in aerospace engineering, nuclear industry, and radiotherapy equipment. These applications are unavoidably exposed to space-like radiation, which has a relative low radiation dose rate at 10-2-10-6 rad(Si)/s. For these reasons, it is necessary to understand the low-dose-rate radiation response of high-k materials based on Si and Ge MOS devices. The radiation response of high-k materials such as radiation-induced oxide and interface trap density have been typically examined by carrying out off-site capacitance-voltage (CV) measurements. However, the conventional and off-site radiation response measurements may underestimate the degradation of MOS devices. In this study, a semi-automated laboratory-scale real-time and on-site radiation response testing system was developed to evaluate the radiationresponse. The system is capable of estimating the radiation response of MOS devices whilst the devices are continuously irradiated by -rays raysrays. Moreover, the complete CV characteristics of MOS capacitors were measured in a relatively short time. The pulse CV measurement reduces the impact of charge trapping behavior on the measurement results, when compared to conventional techniques. The total ionizing dose radiation effect on HfO2 dielectric thin films prepared by atomic layer deposition (ALD) has been investigated by the proposed measurement system. The large bidirectional ΔVFB of the irradiated HfO2 capacitor was mainly attributed to the radiation-induced oxide trapped charges, which were not readily compensated by bias-induced charges produced over the measurement timescales of less than 5 ms. Radiation response of Ge MOS capacitors with HfO2 and HfxZr1-xOy gate dielectrics was also investigated. It was found that radiation-induced interface traps were the dominant factor for Flat-band Voltage shift (ΔVFB) in HfO2 thin films, whereas the radiation response for Zr-containing dielectrics under positive bias was mainly affected by oxide traps. Under positive biased irradiation, the Zr-doped HfxZr1-xOy exhibited smaller ΔVFB than that of HfO2. This is attributed to the de-passivation of Ge-S bonds in capacitors incorporating HfO2 thin films, resulting in the build-up of interface traps. Under negative biased irradiation, ΔVFB was attributed to the combined effect of the net oxide trapped charges and the passivation of Ge dangling bonds at the Ge/high-k interface

Defect Induced Aging and Breakdown in High-k Dielectrics

abstract: High-k dielectrics have been employed in the metal-oxide semiconductor field effect transistors (MOSFETs) since 45 nm technology node. In this MOSFET industry, Moore’s law projects the feature size of MOSFET scales half within every 18 months. Such scaling down theory has not only led to the physical limit of manufacturing but also raised the reliability issues in MOSFETs. After the incorporation of HfO2 based high-k dielectrics, the stacked oxides based gate insulator is facing rather challenging reliability issues due to the vulnerable HfO2 layer, ultra-thin interfacial SiO2 layer, and even messy interface between SiO2 and HfO2. Bias temperature instabilities (BTI), hot channel electrons injections (HCI), stress-induced leakage current (SILC), and time dependent dielectric breakdown (TDDB) are the four most prominent reliability challenges impacting the lifetime of the chips under use. In order to fully understand the origins that could potentially challenge the reliability of the MOSFETs the defects induced aging and breakdown of the high-k dielectrics have been profoundly investigated here. BTI aging has been investigated to be related to charging effects from the bulk oxide traps and generations of Si-H bonds related interface traps. CVS and RVS induced dielectric breakdown studies have been performed and investigated. The breakdown process is regarded to be related to oxygen vacancies generations triggered by hot hole injections from anode. Post breakdown conduction study in the RRAM devices have shown irreversible characteristics of the dielectrics, although the resistance could be switched into high resistance state.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

Sigma-Delta control of charge trapping in heterogeneous devices

Dielectric charging represents a major reliability issue in a variety of semiconductor devices. The accumulation of charge in dielectric layers of a device often alters its performance, affecting its circuital features and even reducing its effective lifetime. Although several contributions have been made in order to mitigate the undesired effects of charge trapping on circuit performance, dielectric charge trapping still remains an open reliability issue in several applications. The research work underlying this Thesis mainly focuses on the design, analysis and experimental validation of control strategies to compensate dielectric charging in heterogeneous devices. These control methods are based on the application of specifically designed voltage waveforms that produce complementary effects on the charge dynamics. Using sigma-delta loops, these controls allow to set and maintain, within some limits, the net trapped charge in the dielectric to desired levels that can be changed with time. This allows mitigating long-term reliability issues such as capacitance-voltage (C-V) shifts in MOS and MIM capacitors. Additionally, the bit streams generated by the control loops provide real-time information on the evolution of the trapped charge. The proposed controls also allow compensating the effects of the charge trapping due to external disturbances such as radiation. This has been demonstrated experimentally with MOS capacitors subjected to various types of ionizing radiation (X-rays and gamma rays) while a charge control is being applied. This approach opens up the possibility of establishing techniques for active compensation of radiation-induced charge in MOS structures as well as a new strategy for radiation sensing. A modeling strategy to characterize the dynamics of the dielectric charge in MOS capacitors is also presented. The diffusive nature of the charge trapping phenomena allows their behavioral characterization using Diffusive Representation tools. The experiments carried out demonstrate a very good matching between the predictions of the model and the experimental results obtained. The time variations in the charge dynamics due to changes in the volatges applied and/or due to external disturbances have been also investigated and modeled. Moreover, the charge dynamics of MOS capacitors under sigma-delta control is analyzed using the tools of Sliding Mode Controllers for an infinite sampling frequency approximation. A phenomenological analytical model is obtained which allows to predict and analyze the sequence of control signals. This model has been successfully validated with experimental data. Finally, the above control strategies are extended to other devices such as eMIM capacitors and perovskite solar cells. Preliminary results including open loop and closed loop control experiments are presented. These results demonstrate that the application of the controls allows to set and stabilize both the C-V characteristic of an eMIM capacitor and the current-voltage characteristic (J-V) of a perovskite solar cell.La carga atrapada en dieléctricos suele implicar un problema importante de fiabilidad en muchos dispositivos semiconductores. La acumulación de dicha carga, normalmente provocada por las tensiones aplicadas durante el uso del dispositivo, suele alterar el rendimiento de éste con el tiempo, afectar sus prestaciones a nivel de circuital e, incluso, reducir su vida útil. Aunque durante años se han realizado muchos trabajos para mitigar sus efectos no deseados, sobre todo a nivel circuital, la carga atrapada en dieléctricos sigue siendo un problema abierto que frena la aplicabilidad práctica de algunos dispositivos. El trabajo de investigación realizado en esta Tesis se centra principalmente en el diseño, análisis y validación experimental de estrategias de control para compensar la carga atrapada en dieléctricos de diversos tipos de dispositivos, incluyendo condensadores MOS, condensadores MIM fabricados con nanotecnología y dispositivos basados en perovskitas. Los controles propuestos se basan en utilizar formas de onda de tensión, específicamente diseñadas, que producen efectos complementarios en la dinámica de la carga. Mediante el uso de lazos sigma-delta, estos controles permiten establecer y mantener, dentro de unos límites, la carga neta atrapada en el dieléctrico a valores prefijados, que pueden cambiarse con el tiempo. Esto permite mitigar problemas de fiabilidad a largo plazo como por ejemplo las derivas de la curva capacidad-tensión (C-V) en condensadores MOS y MIM. Adicionalmente, las tramas de bits generadas por los lazos de control proporcionan información en tiempo real sobre la evolución de la carga. Los controles propuestos permiten también compensar los efectos de la carga atrapada en dieléctricos debida a perturbaciones externas como la radiación. Esto se ha demostrado experimentalmente con condesadores MOS sometidos a diversos tipos de radiación ionizante (rayos X y gamma) mientras se les aplicaba un control de carga. Este resultado abre la posibilidad tanto de establecer técnicas de compensación activa de carga inducida por radiación en estructuras MOS, como una nueva estrategia de sensado de radiación. Se presenta también una estrategia de modelado para caracterizar la dinámica de la carga dieléctrica en condensadores MOS. La naturaleza difusiva de los fenómenos de captura y eliminación de carga en dieléctricos permite caracterizar dichos fenómenos empleando herramientas de Representación Difusiva. Los experimentos realizados demuestran una muy buena correspondencia entre las predicciones del modelo y los resultados experimentales obtenidos. Se muestra también como las variaciones temporales de los modelos son debidas a cambios en las formas de onda de actuación del dispositivo y/o a perturbaciones externas. Además, la dinámica de carga en condensadores MOS bajo control sigma-delta se analiza utilizando herramientas de control en modo deslizante (SMC), considerando la aproximación de frecuencia de muestreo infinita. Con ello se obtiene un modelo analítico simplificado que permite predecir y analizar con éxito la secuencia de señales de control. Este modelo se ha validado satisfactoriamente con datos experimentales. Finalmente, las estrategias de control anteriores se han extendido a otros dispositivos susceptibles de sufrir efectos de carga atrapada que pueden afectar su fiabilidad. Así, se han llevado a cabo experimentos preliminares cuyos resultados demuestran que la aplicación de controles de carga permite controlar y estabilizar la característica C-V de un condensador eMIM y la característica corriente-tensión (J-V) de una célula solar basada en perovskitas

Sigma-Delta control of charge trapping in heterogeneous devices

Dielectric charging represents a major reliability issue in a variety of semiconductor devices. The accumulation of charge in dielectric layers of a device often alters its performance, affecting its circuital features and even reducing its effective lifetime. Although several contributions have been made in order to mitigate the undesired effects of charge trapping on circuit performance, dielectric charge trapping still remains an open reliability issue in several applications. The research work underlying this Thesis mainly focuses on the design, analysis and experimental validation of control strategies to compensate dielectric charging in heterogeneous devices. These control methods are based on the application of specifically designed voltage waveforms that produce complementary effects on the charge dynamics. Using sigma-delta loops, these controls allow to set and maintain, within some limits, the net trapped charge in the dielectric to desired levels that can be changed with time. This allows mitigating long-term reliability issues such as capacitance-voltage (C-V) shifts in MOS and MIM capacitors. Additionally, the bit streams generated by the control loops provide real-time information on the evolution of the trapped charge. The proposed controls also allow compensating the effects of the charge trapping due to external disturbances such as radiation. This has been demonstrated experimentally with MOS capacitors subjected to various types of ionizing radiation (X-rays and gamma rays) while a charge control is being applied. This approach opens up the possibility of establishing techniques for active compensation of radiation-induced charge in MOS structures as well as a new strategy for radiation sensing. A modeling strategy to characterize the dynamics of the dielectric charge in MOS capacitors is also presented. The diffusive nature of the charge trapping phenomena allows their behavioral characterization using Diffusive Representation tools. The experiments carried out demonstrate a very good matching between the predictions of the model and the experimental results obtained. The time variations in the charge dynamics due to changes in the volatges applied and/or due to external disturbances have been also investigated and modeled. Moreover, the charge dynamics of MOS capacitors under sigma-delta control is analyzed using the tools of Sliding Mode Controllers for an infinite sampling frequency approximation. A phenomenological analytical model is obtained which allows to predict and analyze the sequence of control signals. This model has been successfully validated with experimental data. Finally, the above control strategies are extended to other devices such as eMIM capacitors and perovskite solar cells. Preliminary results including open loop and closed loop control experiments are presented. These results demonstrate that the application of the controls allows to set and stabilize both the C-V characteristic of an eMIM capacitor and the current-voltage characteristic (J-V) of a perovskite solar cell.La carga atrapada en dieléctricos suele implicar un problema importante de fiabilidad en muchos dispositivos semiconductores. La acumulación de dicha carga, normalmente provocada por las tensiones aplicadas durante el uso del dispositivo, suele alterar el rendimiento de éste con el tiempo, afectar sus prestaciones a nivel de circuital e, incluso, reducir su vida útil. Aunque durante años se han realizado muchos trabajos para mitigar sus efectos no deseados, sobre todo a nivel circuital, la carga atrapada en dieléctricos sigue siendo un problema abierto que frena la aplicabilidad práctica de algunos dispositivos. El trabajo de investigación realizado en esta Tesis se centra principalmente en el diseño, análisis y validación experimental de estrategias de control para compensar la carga atrapada en dieléctricos de diversos tipos de dispositivos, incluyendo condensadores MOS, condensadores MIM fabricados con nanotecnología y dispositivos basados en perovskitas. Los controles propuestos se basan en utilizar formas de onda de tensión, específicamente diseñadas, que producen efectos complementarios en la dinámica de la carga. Mediante el uso de lazos sigma-delta, estos controles permiten establecer y mantener, dentro de unos límites, la carga neta atrapada en el dieléctrico a valores prefijados, que pueden cambiarse con el tiempo. Esto permite mitigar problemas de fiabilidad a largo plazo como por ejemplo las derivas de la curva capacidad-tensión (C-V) en condensadores MOS y MIM. Adicionalmente, las tramas de bits generadas por los lazos de control proporcionan información en tiempo real sobre la evolución de la carga. Los controles propuestos permiten también compensar los efectos de la carga atrapada en dieléctricos debida a perturbaciones externas como la radiación. Esto se ha demostrado experimentalmente con condesadores MOS sometidos a diversos tipos de radiación ionizante (rayos X y gamma) mientras se les aplicaba un control de carga. Este resultado abre la posibilidad tanto de establecer técnicas de compensación activa de carga inducida por radiación en estructuras MOS, como una nueva estrategia de sensado de radiación. Se presenta también una estrategia de modelado para caracterizar la dinámica de la carga dieléctrica en condensadores MOS. La naturaleza difusiva de los fenómenos de captura y eliminación de carga en dieléctricos permite caracterizar dichos fenómenos empleando herramientas de Representación Difusiva. Los experimentos realizados demuestran una muy buena correspondencia entre las predicciones del modelo y los resultados experimentales obtenidos. Se muestra también como las variaciones temporales de los modelos son debidas a cambios en las formas de onda de actuación del dispositivo y/o a perturbaciones externas. Además, la dinámica de carga en condensadores MOS bajo control sigma-delta se analiza utilizando herramientas de control en modo deslizante (SMC), considerando la aproximación de frecuencia de muestreo infinita. Con ello se obtiene un modelo analítico simplificado que permite predecir y analizar con éxito la secuencia de señales de control. Este modelo se ha validado satisfactoriamente con datos experimentales. Finalmente, las estrategias de control anteriores se han extendido a otros dispositivos susceptibles de sufrir efectos de carga atrapada que pueden afectar su fiabilidad. Así, se han llevado a cabo experimentos preliminares cuyos resultados demuestran que la aplicación de controles de carga permite controlar y estabilizar la característica C-V de un condensador eMIM y la característica corriente-tensión (J-V) de una célula solar basada en perovskitas.Postprint (published version

The Investigation of Fabrication and Reliability of Solution-Processed High-k Dielectrics

Solution-processed high-k dielectrics have become a strong research focus in both academic and industrial fields. However, solution-processing brings poor film quality and stability. Increasing the reliability of solution-processed devices becomes challenging, especially those devices for nuclear and aerospace applications. To address this issue, this work focuses on the fabrication and reliability investigation of solution-processed high-k dielectrics and devices and provide an insight into their bias-stress (BS) and biased radiation stress (BRS) stability degradation. In chapter 3, the annealing effects on the aqueous solution-processed AlOx thin films were investigated. On-site radiation measurements were carried out to analyze the BS and BRS stability of AlOx metal-oxide-semiconductor capacitors (MOSCAPs) under 92 Gy (SiO2) γ-ray radiation. It was found that aqueous solution-processed AlOx thin films with reduced impurities, low leakage current, and satisfied BS stability could be successfully formed at annealing temperature > 250 oC. Compared to the Al2O3 thin films fabricated by atomic layer deposition (ALD), the BRS stability of aqueous solution-processed AlOx thin films is mainly degraded by radiation-induced oxide traps related to the precursor impurities and loosely bonded oxygen. The findings of this chapter offer clear inspiration for achieving highly stable solution-processed high-k dielectrics working in harsh radiation environments. In chapter 4, it is demonstrated that hydrogen peroxide (H2O2) is a strong oxidizer to improve the thin film quality and stabilities of solution-processed dielectrics. Their interface trap density was reduced, and the BS stress stability of AlOx MOSCAPs was improved. Furthermore, 7.5 M H2O2-AlOx MOSCAPs exhibit ignorable radiation-induced oxide and interface traps with total dose up to 42 Gy (SiO2) through carrying out on-site measurements. The 7.5 M H2O2-AlOx MOSCAPs also demonstrate the ability to recover after the bias was interrupted. The results demonstrate that employing H2O2 in the solution-process has significant potential to improve the stabilities of large-area electronics for nuclear and aerospace applications. In chapter 5, the effects of lanthanum composition on the ambient air stability, BS stability and radiation hardness of the water-induced (WI) solution-processed ZrLaO thin films and InOx/ZrLaO thin film transistors (TFTs) were investigated. The ZrLaO thin films with 10% La have remained stable under 5-weeks ambient air exposure and 1.44 kGy γ-ray irradiation. The InOx/Zr0.9La0.1Oy TFTs exhibited satisfied ambient air stability (10-days ambient air exposure) and radiation hardness (1.03 kGy irradiation). The optimized InOx/ZrLaO TFT with 10 % La exhibited a low operating voltage of 4 V and a high Ion/Ioff of around 2 × 106. Besides, their application in resistor-loaded inverters with a gain of 12 at 4 V was also demonstrated. The results represent a great step toward the achievement of low-cost, low-power consumption and large-area flexible electronics working in harsh radiation environments

Integrated Circuits/Microchips

With the world marching inexorably towards the fourth industrial revolution (IR 4.0), one is now embracing lives with artificial intelligence (AI), the Internet of Things (IoTs), virtual reality (VR) and 5G technology. Wherever we are, whatever we are doing, there are electronic devices that we rely indispensably on. While some of these technologies, such as those fueled with smart, autonomous systems, are seemingly precocious; others have existed for quite a while. These devices range from simple home appliances, entertainment media to complex aeronautical instruments. Clearly, the daily lives of mankind today are interwoven seamlessly with electronics. Surprising as it may seem, the cornerstone that empowers these electronic devices is nothing more than a mere diminutive semiconductor cube block. More colloquially referred to as the Very-Large-Scale-Integration (VLSI) chip or an integrated circuit (IC) chip or simply a microchip, this semiconductor cube block, approximately the size of a grain of rice, is composed of millions to billions of transistors. The transistors are interconnected in such a way that allows electrical circuitries for certain applications to be realized. Some of these chips serve specific permanent applications and are known as Application Specific Integrated Circuits (ASICS); while, others are computing processors which could be programmed for diverse applications. The computer processor, together with its supporting hardware and user interfaces, is known as an embedded system.In this book, a variety of topics related to microchips are extensively illustrated. The topics encompass the physics of the microchip device, as well as its design methods and applications

Selected topics on advanced electron devices and their circuit applications

Master'sMASTER OF ENGINEERIN

The Effects of Radiation on Memristor-Based Electronic Spiking Neural Networks

In this dissertation, memristor-based spiking neural networks (SNNs) are used to analyze the effect of radiation on the spatio-temporal pattern recognition (STPR) capability of the networks. Two-terminal resistive memory devices (memristors) are used as synapses to manipulate conductivity paths in the network. Spike-timing-dependent plasticity (STDP) learning behavior results in pattern learning and is achieved using biphasic shaped pre- and post-synaptic spikes. A TiO2 based non-linear drift memristor model designed in Verilog-A implements synaptic behavior and is modified to include experimentally observed effects of state-altering, ionizing, and off-state degradation radiation on the device. The impact of neuron “death” (disabled neuron circuits) due to radiation is also examined. In general, radiation interaction events distort the STDP learning curve undesirably, favoring synaptic potentiation. At lower short-term flux, the network is able to recover and relearn the pattern with consistent training, although some pixels may be affected due to stability issues. As the radiation flux and duration increases, it can overwhelm the leaky integrate-and-fire (LIF) post-synaptic neuron circuit, and the network does not learn the pattern. On the other hand, in the absence of the pattern, the radiation effects cumulate, and the system never regains stability. Neuron-death simulation results emphasize the importance of non-participating neurons during the learning process, concluding that non-participating afferents contribute to improving the learning ability of the neural network. Instantaneous neuron death proves to be more detrimental for the network compared to when the afferents die over time thus, retaining the network’s pattern learning capability