Effects of sputtering and annealing temperatures on MOS capacitor with HfTiON gate dielectric

In this work, Al/HfTiON/n-Si capacitors with different sputtering and annealing temperatures are studied. Larger accumulation capacitance and flat-band voltage are observed for samples with higher sputtering or post-deposition annealing temperature. Gate conduction mechanisms are only affected by sputtering temperature slightly. The flat-band voltage shift and interface-state density at midgap under high-field gate injection and substrate injection are investigated, and the results imply electron detrapping in the gate dielectric. ©2009 IEEE.published_or_final_versionThe IEEE International Conference of Electron Devices and Solid-State Circuits (EDSSC 2009), Xi'an, China, 25-27 December 2009. In Proceedings of EDSSC, 2009, p. 209-21

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

Reliability Analysis of Hafnium Oxide Dielectric Based Nanoelectronics

With the physical dimensions ever scaling down, the increasing level of sophistication in nano-electronics requires a comprehensive and multidisciplinary reliability investigation. A kind of nano-devices, HfO2-based high-k dielectric films, are studied in the statistical aspect of reliability as well as electrical and physical aspects of reliability characterization, including charge trapping and degradation mechanisms, breakdown modes and bathtub failure rate estimation. This research characterizes charge trapping and investigates degradation mechanisms in high-k dielectrics. Positive charges trapped in both bulk and interface contribute to the interface state generation and flat band voltage shift when electrons are injected from the gate under a negative gate bias condition.A negligible number of defects are generated until the stress voltage increases to a certain level. As results of hot electrons and positive charges trapped in the interface region, the difference in the breakdown sequence is attributed to the physical thickness of the bulk high-k layer and the structure of the interface layer. Time-to-breakdown data collected in the accelerated life tests are modeled with a bathtub failure rate curve by a 3-step Bayesian approach. Rather than individually considering each stress level in accelerating life tests (ALT), this approach derives the change point and the priors for Bayesian analysis from the time-to-failure data under neighborhood stresses, based on the relationship between the lifetime and stress voltage. This method can provide a fast and reliable estimation of failure rate for burn-in optimization when only a small sample of data is available

An investigation of high-k materials in metal-insulator-metal capacitor structures

Metal insulator metal (MIM) capacitors are vital components of many devices such as communication band beamformers, medical, automotive, RF IC’s and memory applications. Current MIM capacitors technology utilises low dielectric constant (k) materials (k~3.9 - 7), these materials achieve the required electrical properties of high electric field breakdown strength and minimal leakage current. The low k value of the current materials presents a challenge to development of many new technologies and the integration of high-k materials in MIM capacitor structures is vital to overcome this. In this work we investigate the electrical properties of a hafnium silicate material system in MIM capacitors with sputtered aluminium electrodes. A conduction mechanism study was performed and an investigation of the dielectric reliability was carried out using the time dependent dielectric breakdown methodology. The material was determined to have excellent reliability characteristics. In addition, further samples of the above hafnium silicate capacitors were irradiated with total radiation dosages of 16 krad(Si) and 78 krad(Si). The electrical properties of both samples were characterised and their reliability characteristics were determined. The 16 krad(Si) sample was determined to have excellent radiation hardness and the 78 krad(Si) sample displayed a minor decrease in overall performance. Furthermore, we investigate the growth of hafnium silicate films by plasma assisted atomic layer deposition on metal electrodes and compare with a previous growth study which exhibited excellent electrical properties over a range of substrate materials. In this study the dielectric growth was influenced by the bottom electrode material. High resolution transmission electron microscopy (HRTEM) analysis and Raman spectroscopy indicate that the main crystalline phase is monoclinic HfO2 (k ~18). The scanning transmission electron microscopy (STEM) analysis reveals the presence of nanoparticles, located at the HfO2 grain boundaries. Based on energy-dispersive x-ray spectroscopy (EDX) analysis the nanoparticles are consistent with silicon oxide inclusions

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

Solution processed metal oxide microelectronics: from materials to devices

Owing to their many interesting characteristics, the application of metal oxide based electronics has been growing at a considerable rate for the past ten years. High performance, optical transparency, chemical stability and suitability toward low cost deposition methods make them well suited to a number of new and interesting application areas which conventional materials such as silicon, or more recently organic materials, are unable to satisfy.The work presented in this thesis is focussed on the optimisation of high performance metal oxide based electronics combined with use of spray pyrolysis, as a low cost deposition method. The findings presented here are split into three main areas, starting with an initial discussion on the physical and electronic properties of films deposited by spray pyrolysis. The results demonstrate a number of deposition criteria that aid in the optimisation and fabrication of high performance zinc oxide (ZnO) based thin-film transistors (TFTs) with charge carrier mobilities as high a 20 cm2/Vs. Solution processed gallium oxide TFTs with charge carrier mobilities of ~0.5 cm2/Vs are also demonstrated, highlighting the flexibility of the deposition method. The second part of the work explores the use of facile chemical doping methods suitable for spray pyrolysed ZnO based TFTs. By blending different precursor materials in solution prior to deposition, it has been possible to adjust certain material characteristics, and in turn device performance. Through the addition of lithium it has been possible alter the films grain structure, leading to significantly improved charge carrier mobilities as high as ~54 cm2/Vs. Additionally the inclusion of beryllium during film deposition has been demonstrated to control TFT threshold voltages, leading to improved integrated circuit performance. The final segment of work demonstrates the flexibility of spray pyrolysis through the deposition of a number of high-k dielectric materials. These high performance dielectrics are integrated into the fabrication of TFTs already benefiting from the findings of the previously discussed work, leading to highly optimised low-voltage TFTs. The performance of these devices represent some of best currently available from solution processed ZnO TFTs with charge carrier mobilities as high as 85 cm2/Vs operating at 3.5 V.Open Acces

Radiation Effects on the Electrical Properties of Hafnium Oxide Based MOS Capacitors

Hafnium oxide-based MOS capacitors were investigated to determine electrical property response to radiation environments. In situ capacitance versus voltage measurements were analyzed to identify voltage shifting as a result of changes to trapped charge with increasing dose of gamma, neutron, and ion radiation. In situ measurements required investigation and optimization of capacitor fabrication to include dicing, cleaning, metalization, packaging, and wire bonding. A top metal contact of 200 angstroms of titanium followed by 2800 angstroms of gold allowed for repeatable wire bonding and proper electrical response. Gamma and ion irradiations of atomic layer deposited hafnium oxide on silicon devices both resulted in a midgap voltage shift of no more than 0.2 V toward less positive voltages. This shift indicates recombination of radiation induced positive charge with negative trapped charge in the bulk oxide. Silicon ion irradiation caused interface effects in addition to oxide trap effects that resulted in a flatband voltage shift of approximately 0.6 V also toward less positive voltages. Additionally, no bias dependent voltage shifts with gamma irradiation and strong oxide capacitance room temperature annealing after ion irradiation was observed. These characteristics, in addition to the small voltage shifts observed, demonstrate the radiation hardness of hafnium oxide and its applicability for use in space systems