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SiC Schottky Diodes for Harsh Environment Space Applications

This paper reports on the fabrication technology and packaging strategy for 300-V 5-A silicon carbide Schottky diodes with a wide temperature operation range capability (between -170 °C and 300 °C). These diodes have been designed for harsh environment space applications such as inner Solar System exploration probes. Different endurance tests have been performed to evaluate the diode behavior when working at a high temperature and under severe thermal cycling conditions (ranged from -170 °C to 270 °C). The radiation hardness capability has been also tested. It has been found that the hermeticity of the package in a neutral atmosphere is a key aspect to avoid an electrical parameter drift. Moreover, the use of gold metallization and gold wire bonds on the anode allows reducing the diode surface and bonding degradation when compared to Al-containing technology. On the back-side cathode contact, the Ti/Ni/Au metallization and AuGe combination have shown a very good behavior. As a result, the manufactured diodes demonstrated high stability for a continuous operation at 285 °C.

Thermomechanical Assessment of Die-Attach Materials for Wide Bandgap Semiconductor Devices and Harsh Environment Applications

Currently, the demand by new application scenarios of increasing operating device temperatures in power systems is requiring new die-attach materials with higher melting points and suitable thermomechanical properties. This makes the die-attach material selection, die-attaching process, and thermomechanical evaluation a real challenge in nowadays power packaging technology. This paper presents a comparative analysis of the thermomechanical performance of high-temperature die-attach materials (sintered nano-Ag, AuGe, and PbSnAg) under harsh thermal cycling tests. This study is carried out using a test vehicle formed by four dice (considering Si and SiC semiconductors) and Cu substrates. Thermally cycled test vehicles have been thermomechanically evaluated using die-shear tests and acoustic microscopy inspections. Besides, special attention is paid to set up a nano-Ag sintering process, in which the effects of sintering pressure or substrate surface state (roughness and surface activation) on the die-attach layer are analyzed. As a main result, this study shows that the best die-attach adherence is obtained for nano-Ag when pressure is applied on the dice (using a specifically designed press) during the sintering process (11 MPa provided die-shear forces of 53 kgf). However, this die-attach presents a faster thermomechanical degradation under harsh thermal cycling tests than other considered high-temperature die-attach materials (AuGe and PbSnAg) and PbSnAg shows the best thermomechanical performances.

SiC Integrated Circuit Control Electronics for High-Temperature Operation

This paper is an important step toward the development of complex integrated circuit (IC) control electronics that have to attend to high-temperature environment power applications. We present in premiere a prototype set of essential mixed-signal ICs on SiC capable of controlling power switches and a lateral power MESFET able to operate at high temperatures, all embedded on the same chip. Also, we report for the first time the functionality of standard Si-CMOS topologies on SiC for the master-slave data flip-flop (FF) and data-reset FF digital building blocks designed with MESFETs. Concretely, we present the complete development of SiC-MESFET IC circuitry, able to integrate gate drivers for SiC power devices. This development is based on the mature and stable Tungsten-Schottky interface technology used for the fabrication of stable SiC Schottky diodes for the European Space Agency Mission BepiColombo.

Design of logic gates for high temperature and harsh radiation environment made of 4H-SiC MESFET

Silicon carbide MESFETs are very attractive devices for high frequency applications, and communications. Progresses in the manufacturing of high quality SiC substrates open the possibility to new circuit applications. SiC unipolar transistors, such as JFETs and MESFETs have also a promising potential for digital integrated circuits operating at high temperature (HT) and/or in harsh environments. An increasing demand for HT compliant circuits comes from intelligent power management, automotive industry, and intelligent sensors for harsh environment, space and aerospace as well. The present work is a demonstration of logic gates design with normally-on 4H-SiC MESFET devices using HT Spice models extracted from experimental measurements. A complete library of functional HT logic gates allows the implementation of complex logic embedded in power management circuitry.

Silicon carbide Schottky and ohmic contact process dependence

Abstract The paper investigates the impact of temperature and other annealing conditions on experimental Schottky and ohmic characteristics of fabricated Ni/4HSiC and Ti/4HSiC Schottky diodes. The backside ohmic contact is always Ni/4HSiC. The ohmic contact characteristics greatly improve if the annealing is performed at high temperature×time product. The measurements of Ni/4HSiC Schottky show a decrease of the Schottky barrier height when increasing the annealing temperature. In the case of the Ti–Schottky contacts, the lowest Schottky barrier height was obtained for diodes annealed into H 2 ambient.

Accelerated test for reliability analysis of SiC diodes

The purpose of this work is the analysis of reliable wire bonding schemes for power SiC diodes working at high temperature. The surge current and the power cycling behavior of different wire bonding technologies are analyzed. A dedicated test bench was developed for the surge current and the power cycling reliability tests [1], [2], [3], [4]. It allows an accelerated reliability test, 105 cycles takes just 3 hours. The 10ms half-sinusoidal current pulse test allows observing the effect of the diodes self-heating. The power cycling capability was analyzed using a new concept [1] of observing the evolution of the dissipated energy per pulse, whose increase under constant current test pulse indicates the degradation of the device. These tests were helpful for chosen an enhanced bonding technology able to work at Tjunctio=300°C.)

Demonstration of temperature compensated voltage reference integrated circuit designed with 4H-SiC MESFETs

This work demonstrate for the first time a functional high temperature compensated Voltage Reference integrated circuit (IC) on 4H-SiC material, built with MESFET devices. A special finger type MESFET that overcome the typical embedded drain leakage of finger type MESFET, was developed for this purpose. The schematic and the principle of the circuit is based on a new concept design that avoid the bandgap reference topology and the necessity of using an operational amplifier (OpAmp), which is not yet developed on SiC. The experimental temperature coefficient (TC) is significantly better than a Zener diode and comparable to the normal bandgap voltage references on silicon, but the present circuit has the advantage to be able to work beyond 250oC. The circuit contains also a linear temperature sensor.

A HfO 2 based 800V/300°C Au-free AlGaN/GaN-on-Si HEMT technology

Innovative 800V/300°C AlGaN/GaN-on-Si high electron mobility transistors (HEMTs) fabricated with a 4-inch Si CMOS compatible technology are presented in this paper. High performance AlGaN/GaN MIS gated HEMT (MIS-HEMT) and passivated HEMT (i-HEMT) were fabricated using 5nm-thick HfO₂, and 30nm-thick CVD Si₃N₄ as the gate and passivation insulator, respectively. Contact resistance maps yield reduced R_c of 1.32±0.26 Ωmm for Au-free compared to 0.86±0.58 Ωmm for conventional Au-based Ohmic metallization. The off-state breakdown voltage is around 800V with a specific on-resistance of 2 mΩcm². Gate and drain leakage currents as well as dynamic I-V trapping are significantly improved with the MIS-HEMT architecture with almost no trade-off to the on-state.

Design of Digital Electronics for High Temperature Using Basic Logic Gates Made of 4H-SiC MESFETs

– 4H-SiC MESFET transistors are very attractive devices for high temperature application and communications. The JFET and MESFET transistors have a promising potential for integrated circuits able to operate at high temperature and harsh radiation environments, due to the superior electrical, mechanical and chemical proprieties of 4H-SiC. Progresses in the manufacturing of high quality SiC substrates open the possibility to new circuit applications.

4H-SiC MESFET specially designed and fabricated for high temperature integrated circuits

Due to its wide bandgap, 4H-SiC is a potential candidate for developing devices capable to operate at elevated temperatures. Nowadays there is an increasing demand for high temperature circuits for drivers of SiC switches applicable to intelligent power management, automotive industry, intelligent sensors for harsh environment, space and aerospace among others. This paper is presenting high temperature experimental results in the 25°C-300°C temperature range of the 4H-SiC planar-MESFET specially designed and fabricated for high density SiC integrated circuits implementation.