Leakage current analysis using high resistivity Silicon gated diodes for PIN detectors application

In recent years, a high resistivity silicon (HR-Si) substrate is of interest as a substrate upon which integrated radio-frequency (RF) and millimeter wave circuits can be realized. Because the material have an inherent defect density, surface effect and resistivity degradation near the interface between an insulating oxide and a HR-Si substrate tend to overshadow the potentially low RF loss levels in HR-Si substrate. Fixed positive charges within the oxide attract free carriers near the substrate surface, leading to an accumulation or inversion layer on the silicon surface. Consequently, these free carriers act as the thin surface-channel at the Si/oxide interface, thus reducing the resistivity of the silicon surface and increasing the substrate loss. In fact, several surface passivation approaches have been used to overcome these shortcomings. For example, local resistivity can be enhanced by high-dose implantation (e.g, argon) to convert LR-Si substrate to HR-Si substrate [1], or a trap-rich passivation layer (e.g., polysilicon or amorphous silicon) between the oxide layer and the HR-Si substrate to prevent the carrier accumulation [2]. Polysilicon films deposited by LPCVD are the most widely used as a surface passivation layer on on HR-Si substrate and a thickness between 300nm and 400 nm were generally used. For HR-Si surface passivation application, the properties of LPCVD-deposited polysilicon (or amorphous silicon) are known to be significantly dependent on deposition conditions and annealing conditions [3].

Silicon has many advantages as a microwave substrate material including low cost and a mature technology. The aim of this paper is to evaluate the potential of using high-resistivity silicon as a low-cost low-loss microwave substrate through an experimental comparative study. Coplanar waveguides fabricated on Si, GaAs, and quartz substrates are tested and their characteristics are compared. Microwave spiral inductors and meander lines are also fabricated on various substrates, and their performance is also analyzed. The results demonstrate that the losses of a coplanar transmission line (CPW) realized on high-resistivity (3 k to 7 k /spl Omega/-cm) silicon substrates are comparable to the losses of a CPW realized on a GaAs substrate covered with insulators. Furthermore, measured unloaded Q's of microwave inductive structures on high-resistivity silicon substrates are comparable to the measured unloaded Q's of the same structures on GaAs and on quartz. This paper demonstrates that high-resistivity Si can be used as a microwave substrate.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Radio-Frequency (RF) losses on High-Resistivity Silicon (HRS) substrates were studied for several different surface passivation layers comprising thin-films of SiC, SiN and SiO 2 In many combinations, losses from conductive surface channels were reduced and increasing the number of interfaces between thin-films was found to be beneficial. In some cases the surface losses were completely eliminated. For example, with plasma-enhanced chemical-vapor deposition (PECVD) α-SiC layers up to a few tens of nm thick and exposed to nitridation or SiN growth at 850°C to form a SiC:N interface layer, values for the total losses of 1.6 dB/cm were achieved. Analysis of these layers was performed by using temperature dependent measurements of the RF losses on Coplanar Waveguides (CPWs), the capacitance-voltage characteristics and the sheet resistance along the Si surface. The overall results can be explained by assuming that the thin-films are so defected that they allow vertical current paths to highly-resistive interface layers where both fixed and mobile charge can be stored.

AlGaN/GaN high-electron-mobility-transistors (HEMTs) with 0.8-/spl mu/m- and 0.3 /spl mu/m-gate-length were successfully fabricated on high-resistivity (HR) silicon substrate. The cutoff frequency f/sub T/ values of 7 GHz, 22 GHz and maximum oscillation frequency f/sub max/ values of 23 GHz, 40 GHz were achieved for 0.8-/spl mu/m- and 0.3-/spl mu/m-gate-length device, respectively. A minimum noise figure (NF/sub min/) of 2.0 dB and an associate gain (G/sub ass/) of 10.3 dB were achieved at 10 GHz in 0.3-/spl mu/m-gate-length device. This shows the promising potential of AlGaN/GaN HEMTs on high-resistivity Si for cost effective low noise amplifiers.

In this paper, spiral inductors on high-resistivity silicon (HR-Si) substrates, which surfaces were passivated by different process methods, were fabricated and measured. The comparison of inductances and quality factors between these inductors shows that the inductances and quality factors of spiral inductors significantly depend on process method and thickness of surface passivation layer. The differently generated passivation layer results in different effective substrate resistivity and hence gives rise to different substrate loss. The experimental results show that using thicker nanocrystalline silicon (nc-Si) as a passivation layer will result in a smaller substrate loss and hence spiral inductors on the substrate have larger inductances and larger quality factors. In this study, the metal thickness of inductors is 1.2 µm and is about half that of the inductors provided by foundries. At higher frequencies, the thinner spiral inductors on the SiO2/nc-Si/HR-Si substrate have larger inductances and larger quality factors as compared with the inductors provided by foundries. With the same metal thickness as that adopted in standard processes of foundries, the identical-geometry inductors on the SiO2/nc-Si/HR-Si substrate probably exhibit superior quality factors.

To study the change rules of leakage current of long string insulators under high altitude condition, and using the current to characterize the insulators' running state and pollution level can be highly useful to prevent flashovers from happening. In this paper, waveforms the leakage current of long string insulators under high altitude condition are measured by artificial pollution tests and the amplitude-frequency characteristics of the leakage current are analyzed. The results show that with the increase of leakage current amplitude, the third harmonic content decreases, the current waveform became more sinusoidal, the phase difference between current and voltage reduces. Through the analysis of maximum leakage current of insulator strings in different salt deposit density (SDD), a linear relationship is found between the maximum leakage current and SDD, thus the insulator pollution level can be characterized with leakage current peak value. Through the analysis of leakage peak currents under different altitudes, it is found that the effects of altitude on the leakage current is the same with the influence of altitude on U50, leakage current peak becomes smaller with the increase of altitude, therefore the leakage current of different altitudes can be corrected by an index n which stands for the effect level of altitude drops on the flashover voltage.

Terahertz wire-grid polarizer with 500 nm grating period on high resistivity silicon (100) is fabricated using nanoimprinting lithography (NIL). Preliminary results show a good polarization characteristic ranging from 0.5 to 5 THz. The method is high throughput and low cost.

Pulse characteristics of silicon double barrier optical sensors with signal amplification

Fabrication and characterization of silicon based thermal neutron detector with hot wire chemical vapor deposited boron carbide converter

We investigate the long-term performance of passive millimeterwave microstrip circuits on high resistivity silicon substrates. Three types of test structures were exposed to harsh environmental conditions such as thermal stress, humidity and organic vapors for 400 hours. Measured results at 38 GHz showed excellent long-term stability of the circuits. No significant difference between chips with and without SiO/sub 2/ passivation layer has been found though chips with passivation showed larger photosensitivity and higher loss.

Leakage current frequency components are frequently used as a tool for surface condition monitoring on polymeric insulation material and their pollution severity. Fast Fourier Transform (FFT) is one of the methods that are applied for the analysis, but it has some limitation in non-stationary signal. This paper presents analysis of leakage current on polymeric insulation material for high voltage application in frequency domain and time-frequency representation. Tracking and erosion test (Inclined Plane Test (IPT)) complying with BS EN 60587-2007 is conducted on polymeric insulation to select a set of different leakage current patterns from capacitive, resistive and discharge. Then, the leakage current patterns are analysed in frequency domain and time-frequency representation using Fast Fourier Transform and spectrogram technique, respectively. It is found that the surface condition of polymeric insulation material state can be classified accurately by using spectrogram compared to Fast Fourier Transform.

This paper provides an overview of how CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> cleaning works on energized electrical equipment. Contaminants can significantly reduce the dielectric strength of insulating materials in the electric equipment. These contaminants can cause increased levels of leakage current to pass over dielectric materials, leading to electrical breakdown due to surface tracking. Such conditions can result in flashovers, which can damage electrical equipment and cause unplanned service outages, as well as safety concerns. Experimental procedure to test the effectiveness of CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> cleaning in reducing leakage currents due to contamination is discussed. The CO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> cleaning test results show that the cleaning process can be efficient and safe in cleaning exposed insulating surfaces. The analysis of leakage currents, measured during the cleaning process, indicate that there is a significant number of short duration discharges of leakage current. The number of discharges is reduced significantly as the magnitude of the leakage current increased. The leakage current observed during the process was measured in milliampereres during the short duration discharges, and never exceeded 34mA.

The measurement and analysis of leakage current (LC) for condition-based monitoring and as a means of predicting flashover of polluted insulators has attracted a lot of research in recent years. Leakage current plays an important role in the detection of insulator's condition. This paper proposes a method for reducing the noise included in the current signal. The tests were carried out on cleaned and polluted glass insulators by using surface tracking and erosion test procedure of IEC 60587. Wavelet analysis method is used to compress the leakage current data. Experimental results shows that the actual signals of leakage current are related to the levels of insulator contamination.

This paper introduces the indicators for surge arrester condition assessment based on the leakage current analysis. Maximum amplitude of fundamental harmonic of the resistive leakage current, maximum amplitude of third harmonic of the resistive leakage current and maximum amplitude of fundamental harmonic of the capacitive leakage current were used as indicators for surge arrester condition monitoring. Also, the effects of operating voltage fluctuation, third harmonic of voltage, overvoltage and surge arrester aging on these indicators were studied. Then, obtained data are applied to the multi-layer support vector machine for recognizing of surge arrester conditions. Obtained results show that introduced indicators have the high ability for evaluation of surge arrester conditions.

Leakage current analysis on 50 nm thick ferroelectric Al0.78Sc0.22N films with TiN electrodes has been performed. The electron conduction followed Schottky emission with an initial Schottky barrier height (ϕ B) of 0.46 eV. During the initial switching, a gradual shift in the leakage current was observed, changing the ϕ B to 0.36 eV, and stayed constant for further switching cycles. From the extracted Richardson constant, the change in the ϕ B can be interpreted as the formation of a tunneling barrier due to the formation of nitrogen vacancies at the metal interface.