BaTiO3 based capacitors are critical for power converter functionality. However, they are known to have reliability issues under harsh environments. Thus, it is important to understand the resistance degradation mechanism in high dielectric constant inorganic capacitors. In this paper, the resistance degradation of unintentionally doped single crystal BaTiO3 capacitors has been studied as a function of electric field, temperature, and capacitor size. The experimental data show the degradation behavior of single crystal BaTiO3 depends strongly on the electric field strength. The activation energy for degradation in BaTiO3 capacitors shows a sudden change around the Curie temperature which indicates that the conductivity mechanism above the Curie temperature is different than at low temperature. We observed that unintentionally doped single crystal BaTiO3 capacitors exhibit three distinct stages of degradation, suggesting the presence of multiple conduction mechanisms during the degradation process.

The detection and localization of radiation sources using low-cost, mobile detectors is a challenging application, necessitating new research into sensing devices and detection algorithms. While new sensing that employs small detectors for detecting gamma-rays has emerged, the decreased sensitivity of the sensor makes it challenging to maintain reliability compared to larger detectors. Machine learning could be a viable method for enhancing sensitivity by classifying background radiation spectra from anomalous spectra, but this approach can struggle to identify novel radioactive sources or identify sources in dynamic background environments. To address these challenges, we propose the use of adversarial auto encoders (AAEs) for anomaly detection in radiation sensing systems. With the use of our AAE architecture, we eliminate the need for obtaining examples of radiation anomalies for training data and increase the resilience of the sensing when the background radiation is dynamic. We evaluate the system in various contexts using a custom designed detector, showing the AAE model generalizes to various locations and radiation sources. We also show a real-time field test with the detection system in both handheld and drone mounted testing.

Field Emitter Arrays (FEAs) have the potential to operate at high power, high frequencies, and endure harsh environments. However, vacuum packaging these devices poses a challenge due to the sensitivity of the emission phenomena to the surface properties of the cathode, such as the work function and the tip radius. Studying the effect of different residual gases on FEAs can enhance our understanding of the interaction between the emission surface and the environment and help estimate the permissible amount of residual gases within the package. In this study, the effect of N2 exposure on 500 x 500 Silicon Field Emitter Arrays (Si-FEAs) was investigated. The device was exposed to 10 000 Langmuir (L) of N2 at 10-7 Torr. During the exposure, the anode current increased from 4.7 mu A to 16 mu A. However, this enhancement in current was temporary, and upon closing the leak valve, the anode current gradually returned to the pre-exposure level. No significant change in current was observed when the device was powered off during N2 exposure. The extent of current enhancement showed a direct relationship with the partial pressure of N2. These results suggest that the presence of N2 in a vacuum package does not degrade the performance of Si-FEAs.

Nano-scale vacuum transistors (NVCTs) based on field emission have the potential to operate at high frequencies and withstand harsh environments, such as radiation, high temperatures, and high power. However, they have demonstrated instability and failures over time. To achieve high currents from NVCTs, these devices are typically fabricated in large-scale arrays known as field emitter arrays (FEAs), which share a common gate, cathode, and anode. Consequently, the measured currents come from the entire array, providing limited information about the emission characteristics of individual tips. Arrays can exhibit nonuniform emission behavior across the emitting area. A phosphor screen can be used to monitor the emission pattern of the array. Additionally, visible damage can occur on the surface of the FEAs, potentially leading to the destruction of the gate and emitters, causing catastrophic failure of the FEAs. To monitor damage while operating the device, an ITO-coated glass anode, which is electrically conductive and visible-light-transparent, can be used. In this work, a method was developed to automatically monitor the emission pattern of the emitters and the changes in surface morphology while operating the devices and collecting electrical data, providing real-time information on the failure sequence of the FEAs.

Heavy-ion radiation tolerance of wide-bandgap gallium nitride (GaN) high-electron-mobility transistors (HEMTs) has been studied as a function of bias voltage, ion linear energy transfer (LET), radiation flux, and total fluence. A statistically significant number of heavy-ion-induced gate dielectric breakdowns were observed, including both soft breakdown (SBD) and hard breakdown (HBD) events. Specific fluence-to-failure experiments and constant-fluence experiments were used to explore the gate dielectric degradation mechanism. Our data provide evidence that radiation-induced breakdown is associated with defect-related conduction paths formed across the dielectric in response to radiation-induced charge injection.

Field emitter arrays (FEAs) have the potential to operate at high frequencies and in harsh environments. However, they have been shown to degrade under oxidizing environments. Studying the effect of O2 on FEAs can help to understand the degradation mechanisms, identify the requirements for vacuum packaging, and estimate the lifetime of the device. In this work, the effect of O2 exposure on 100 × 100 gallium-nitride-field emitter arrays (GaN-FEAs) was studied. The GaN-FEAs were operated at 6 × 10−10 Torr with a 1000 V DC anode voltage and a 50 V DC gate voltage, where the anode current was 1 μA and the gate current was ≤4 nA. The devices were exposed to 10−7, 10−6, and 10−5 Torr of O2 for 100 000 L. The anode current dropped by 50% after 300 L and 98% after 100 000 L. It was observed that the degradation depends on the exposure dose, rather than pressure. The devices mostly degrade when they are ON, confirmed by exposing the device to O2 when the gate voltage was off, and also by the relation between the degradation and duty cycle when pulsing the gate. The results of O2 exposure were compared to Ar exposure to determine whether sputtering and changes in the surface geometry were the primary cause of degradation. The results suggest that changes in the work function and surface chemistry are the cause of emission degradation of GaN-FEA induced by O2.

Field emitter arrays (FEAs) have the potential to operate at high frequencies and in harsh environments. However, the vacuum packaging of these devices poses a challenge due to the sensitivity of the emission phenomena to the surface properties of the cathode. Studying the effect of different residual gases on FEAs can help to understand the interaction of the emission surface with the environment and identify the feasibility and requirements for vacuum packaging. In this work, the effect of N2 exposure on 150 × 150 gallium-nitride-field emitter arrays (GaN-FEAs) was studied. The GaN-FEA was first operated at 10−9 Torr with a 1000 V DC anode voltage and a 50 V DC gate voltage, where the anode current was 6 μA. The device was then exposed to 10 000 l N2 at 10−7 Torr, and the anode current increased by 2.7 times during N2 exposure. The increase in the current was not permanent, and the current gradually decreased to its pre-exposure level after the N2 source was cut off. The results of N2 exposure were compared to Ar and O2.

Scintillators are the primary devices used for radiation detection., especially at national borders and other ports of entry. Reducing the size of these detectors for placement on mobile devices such as drones can allow for better detection and localization of radiation sources. Detection of radiation with supervised machine learning can be a challenge when looking for previously unobserved radiation sources. Therefore, anomaly detection methods are investigated. In this work we employ adversarial autoencoders trained to classify spectra from radioactive sources as either background or anomalous. This allows the model to detect anomalies regardless of radiation source and outperform supervised methods on newly encountered sources.

This paper reviews the highlights of where materials science has helped advance silicon-based transistor technology.

Terrestrial neutron-induced single-event gate rupture (SEGR) in a commercial depletion mode gallium nitride (GaN) power high-electron-mobility transistor (HEMT) has been reported in our recent paper. To further understand the neutron-induced failure mechanisms, nuclear event and electronic simulations were performed to model the effect of terrestrial neutron secondary-ion-induced gate dielectric breakdown. Transient device simulations determined ion-induced peak transient electric field and duration for a variety of ion linear energy transfers (LETs), ion injection locations, and applied drain voltages. Results demonstrate that the peak transient electric fields exceed the breakdown strength of the gate dielectric leading to dielectric defect generation and breakdown.

The impact of Oxygen (O 2 ) exposure on Silicon Field Emitter Arrays (Si-FEA) was studied. A 50×50 array of Silicon field emitters was tested at 1000V DC anode and 45V DC gate voltage in 6×10 −10 Torr before 10– 7 Torr partial pressure of O 2 was introduced into the chamber. The results indicate that the anode current degradation rate is approximately 0.1 percent per Langmuir of O 2 exposure. This study can provide guidelines for the vacuum packaging requirements of Si-FEAs.

Adsorption effects of gasses such as N 2 , Ar, He and H 2 O on field emission performance of Silicon Gated Field Emitter Arrays (Si-GFEAs) are of importance. In this work, Si-GFEAs with 1000×1000 tips 1 have been exposed to these gasses after cleaning with ultraviolet light (UV) to remove water vapor 2 . The collector voltage was fixed at 200 V DC, and the gate was held at 40 V for all measurements. Three different partial pressures, 5×10 -6 Torr, 5×10 -5 Torr and 5×10 -4 Torr were used. A residual gas analyzer (RGA) was used to monitor the partial pressure. It was observed that for a gate voltage of 40 V, the collector current decrease for N 2 was 41% at 5×10 -4 torr; whereas Ar had a 65% drop at 5×10 -4 torr. Each test took ≈ 10 minutes. After the exposure, vacuum was restored and the I-V sweep was repeated. After pump down, observed collector current was restored to pre-exposure conditions, though not completely (within 10-15%) . A subsequent UV exposure restored the pre-exposure collector current completely. It was hypothesized that the exposed gasses were adsorbed by emitter tips which increased the work function. However, the RGA also showed that a large percentage of the gas (1%) introduced into the chamber was H 2 O which might have a large impact on work function. Further study is ongoing.

The use of CMOS sensors for rotational spectroscopy is a promising, but challenging avenue for low-cost gas sensing and molecular identification. A main challenge in this approach is that practical CMOS spectroscopy samples contain various different noise sources that reduce the effectiveness of matching techniques for molecular identification with rotational spectroscopy. To help solve this challenge, we develop a software application tool that can demonstrate the feasibility and reliability of detection with CMOS sensor samples. Specifically, the tool characterizes the types of noise in CMOS sample collection and synthesizes spectroscopy files based upon existing databases of rotational spectroscopy samples gathered from other sensors. We use the software to create a large database of plausible CMOS-generated sample files of gases. This dataset is used to help evaluate spectral matching algorithms used in gas sensing and molecular identification applications. We evaluate these traditional methods on the synthesized dataset and discuss how peak finding and spectral matching algorithms can be altered to accommodate the noise sources present in CMOS sample collection.

A 1000×1000 Si FEA went through reliability test. Under fixed gate-voltage, the emission current stays stable at ~3mA over 3 days, but suddenly dropped 92% within one second, while the gate leakage current drops simultaneously. Post-testing physical characterization reveals majority of the emitters within the array keeps their structure integrity. The sudden emission current drop is due to a small amount of shorted/damaged emitters on the edge of the array.

A novel and scalable method enabling the integration of dissimilar thin‐film devices for high density and large‐area sensors is demonstrated. The method is validated by integrating CdS/CdTe P‐N thin‐film diodes with poly‐Si thin‐film transistors (TFTs) in an active pixel sensor (APS) scheme. These devices have been used separately in low‐cost and large‐area applications such as liquid‐crystal displays (Poly‐TFTs) and solar cells (CdS/CdTe) and the methods allow a seamless integration that eliminates the use of discrete pixel‐to‐pixel bumping interconnections. APSs, consisting of a cascode TFT amplifier and a CdS/CdTe diode, are evaluated using pulsed light sources under several wavelengths and intensities. The results demonstrated a responsivity increase of >100× for the integrated sensors and well‐defined signal amplitude, as desirable for energy and intensity monitoring. The method enables the use of two dissimilar and remarkable devices in a wide range of applications such as X‐ray imagers, gamma‐ray detectors, and thermal neutron detectors, while offering large‐area and low‐cost compatibility. More importantly, the integrity and reliability of the diodes and TFTs are not affected by the integration process.

Large arrays of nanoscale silicon field emitters are tested in a UHV system equipped with a phosphor screen. The anode current is measured and the emission pattern is captured at the same time. The emission pattern shows the whole Field Emission Arrays (FEAs) are emitting from the beginning of the test. But as the test progresses, the regions at the edge of the array are more vulnerable and tend to be damaged/shorted first. A few shorted emitters along the edges could reduce the effective gate bias applied to the central region of the array, causing the emission current of the whole array to drop dramatically, and prompt the FEA to fail, while the physical integrity of majority emitters in the array are intact.

We present a detailed study of post-deposition annealing effects on contact resistance of Au, Ti, Hf and Ni electrodes on Mg2Si thin films. Thin-film Mg2Si and metal contacts were deposited using magnetron sputtering. Various post-annealing temperatures were studied to determine the thermal stability of each contact metal. The specific contact resistivity (SCR) was determined using the Cross Bridge Kelvin Resistor (CBKR) method. Ni contacts exhibit the best thermal stability, maintaining stability up to 400 degrees C, with a SCR of approximately 10(-2) Omega-cm(2) after annealing. The increased SCR after high temperature annealing is correlated with the formation of a Mg-Si-Ni mixture identified by cross-sectional scanning transmission electron microscopy (STEM) characterization, X-ray diffraction characterization (XRD) and other elemental analyses. The formation of this Mg-Si-Ni mixture is attributed to Ni diffusion and its reaction with the Mg2Si film. (C) 2017 Elsevier B.V. All rights reserved.