Papers by Author: Gheorghe Brezeanu

Abstract: Two characterization methods are compared in terms of their suitability for predicting the electrical behavior of non-uniform Ni/4H-SiC Schottky contacts up to 450°C, using data measured at lower temperatures. These techniques are based on the established Gaussian distribution of barrier heights model and a recently proposed discrete barrier distribution model, respectively. Two samples with different degrees of contact inhomogeneity are measured and their forward characteristics are fitted using both techniques. The Gaussian distribution approach is shown to accurately fit experimental data only for the nearly-uniform sample, while requiring the extraction of two separate barrier height values from measurements in the room-250°C range, only. When attempting to use this method to characterize the sample with strong non-uniformity, fitting accuracy (given by R²) drops under 90%. In contrast, the discrete barrier distribution technique is proven able to forecast the electrical behavior of both samples (with R² > 99% in most cases), over the entire room-450°C range, using a single Schottky barrier for each device (1.61V, corresponding to a Ni₂Si Schottky contact and 0.9V, afferent to a Ni metallization).

Abstract: Different characterization techniques have been used in order to evaluate the electrical behavior of Pt/SiC-Schottky diodes and determine their capability as temperature sensors. I-V characteristics for fabricated devices were measured up to 400°C. Subsequent conventional parameter extraction evinced a barrier height increase with temperature, suggesting inhomogeneous contact formation. The energy activation method was carried out in order to identify both the effective barrier height for the devices and the non-uniformity parameter (p). Despite severe degrees of contact inhomogeneity, the diodes were found adequate for temperature sensing applications over the 26°C – 400°C range, with sensitivities up to 1.59 mV/°C.

Abstract: This paper proposes a method of characterizing silicon carbide Schottky diodes with inhomogeneous contacts in temperature sensing applications. Using the energy activation technique, temperature intervals where the effective barrier height is constant are determined. Unlike the conventional barrier which increases with temperature for inhomogeneous diodes, the effective barrier has physical meaning and can be used for sensor performance evaluation. The utility of effective barrier analysis is confirmed on fabricated Ni/4H-SiC Schottky diodes with different annealing conditions and different degrees of barrier non-uniformity. The good agreement between calculated and experimental data proves the suitable behavior of inhomogeneous diodes as sensors for different temperature ranges.

Abstract: The electrical behavior and stability of a temperature sensor based on 4H-SiC Schottky diodes using Ni₂Si as Schottky contact, are investigated. The ideality factor and the barrier height were found to be strongly dependent on the post-annealing temperature of the Ni contact (which lead to the formation of Ni₂Si). A nearly ideal Schottky device, with the barrier height approaching the high value of 1.7eV, and a slight temperature dependence, was obtained after an annealing at T_A=800°C. This high barrier height proves that Ni₂Si is suitable as Schottky contact for temperature sensors, able to reliably operate up to 450°C. Sensor sensitivity levels between 1.00mV/°C and 2.70 mV/°C have been achieved.

Abstract: MOS capacitor devices based on silicon carbide (SiC) are largely used as hydrogen detectors in high temperature and chemically reactive environments. A SiC MOS capacitor structure used as hydrogen sensor is analyzed by extensive simulations. The sensitivity to hydrogen detection, stability to temperature variation and dependence on interface states concentration are evaluated. The effects of structure parameters on sensors performance are also investigated. Results show that the oxide layer type and thickness and the SiC polytype have a significant influence on the detectors performance. The proposed optimum structure for high temperature hydrogen detection is based on 3C-SiC substrate and 10nm TiO₂ layer. In accordance with the simulations results, three types of masks are designed for the fabrication of SiC MOS capacitor structures.

Abstract: A partially electrically isolated package with a gold wire and fully isolated solution with a metallic piston, respectively, are designed and tested for high temperature sensors (400°C) based on SiC Schottky barrier diodes (SBD). Electrical behavior and sensor performance are very close for both packaging solutions. The stress due to contact pressure and higher cost are some disadvantages for pressure contact technology.

Abstract: This paper presents an improved version and new results on a temperature sensor based on SiC Schottky Barrier Diode (SBD). SiC SBD structures of different areas were packaged in a metallic-glass case. The encapsulated sensor was electrically measured at several temperatures. A good linearity of the forward voltage measured at a constant current versus temperature dependence was obtained in the temperature range of 150-400°C where the sensor is meant to operate. Optical investigation, correlated with electrical measurements, prove the reliability of the sensor structure and of the package solutions at temperatures up to 400°C.

Abstract: A fully electrically isolated package for a SiC temperature sensor, able to work at high temperature, is presented in this paper. The adopted packaging solution was tested under thermal stress by varying the temperature between 300C and 400C (for 500 cycles) and between 50C and 400C (for other 500 cycles). The thermal stress had negligible effect on the capsules leakage currents (measured from the sensor terminals to the package metal casing) and did not degrade the glass which ensures the sealing of the capsule. The measurements and microphysical investigations showed a stable operation of the package up to temperatures of 400C.

Abstract: 4H-SiC Schottky Barrier Diodes (SBDs) with remarkable electrical performance have been fabricated and characterised. A barrier height about 1.64V and an ideality factor close to 1 are extracted from the forward characteristics measured at several temperatures. These essential Schottky contact parameters are observed to be constant with temperature. A temperature probe with a simple and innovative scheme is designed and applied. The probe uses SiC SBDs as temperature sensor in the 20-4000C range, with measured sensitivities varying from 1.3 mV/K to 2.8 mV/K. The probe is meant to monitorize the temperature inside the furnaces, in the cement industry.

Abstract: This paper presents a comparison between SiC and diamond Schottky barrier diodes using the oxide ramp termination. The influences of the dielectric thickness and relative permittivity on the diode’s electrical performance are investigated. Typical commercial drift layer parameters are used for this study. The extension of the space charge area throughout the drift region and the current distribution at breakdown are shown. The efficiency of the termination is also evaluated for both SiC and diamond diodes.