Carl-Mikael Zetterling

This work describes the fabrication and characterization of a novel lateral 4H-SiC PiN diode featuring inter-device isolation technology for power integrated circuits (ICs). The device’s architecture includes thick SiO₂ blocking layers and inter-device trench isolation structures, enabling effective electrical isolation between power devices and control circuitry on a single chip. The devices demonstrate good isolation performance, with inter-device leakage currents below 5 nA at a reverse bias of 200 V. The diodes keep reverse leakage current low (<1 μA at 20 V), but exhibit non-distinct turn-on behavior. This is mostly due to the too-shallow N+ and P+ ion implantation region and high series resistance. A monolithically integrated bridge circuit operating at 50 Hz and 200 Hz validates the integration approach; however, large forward voltage drops show that the high series resistance at the device level affects overall conversion efficiency. The transfer length method (TLM) characterization reveals high sheet and contact resistances, which are responsible for the conduction limitations in the PiN diode forward performance. This study establishes the foundation for a lateral SiC device technology with promising inter-device isolation capabilities, as well as the bridge circuit built based on the lateral PiN diodes, which shows the potential of this technology for future monolithic power IC applications.

Silicon carbide (SiC) is a key material for electronics operating in harsh environments due to its wide bandgap, high thermal conductivity, and radiation hardness. In this work, we present a SPICE model for a 4H-SiC BJT and TTL inverter exposed to gamma radiation. The devices were fabricated using a dedicated SiC bipolar process at KTH (Sweden) and tested at the ⁶⁰Co Calliope (Italy) facility up to 800 krad _(Si). Experimental data, including Gummel plots and inverter transfer characteristics, were used to calibrate and refine a VBIC-based SPICE model. The adjusted model accounts for both bulk and surface degradation mechanisms by extracting parameters of forward current gain (βF), saturation current (IS), base resistance (RB), and forward transit time (TF). Results show a uniform degradation of BJTs, primarily manifested as reduced current gain and increased base resistance, while the inverter maintained functional operation up to 600 krad_(Si). Extrapolation of the SPICE model predicts a failure threshold near 16 Mrad_(Si), far exceeding the tolerance of conventional silicon circuits. By linking radiation-induced defects at the material and interface levels to circuit-level behavior, the proposed model enables realistic design and lifetime prediction of SiC integrated circuits for satellites, planetary missions, and other radiation-intensive applications.

With its excellent thermal conductivity, high critical breakdown field strength, and high temperature tolerance, Silicon Carbide (SiC) is widely used in the fabrication of power devices. In recent years, many vertical high-voltage SiC PiN diodes with superior performance have been reported. However, since the cathode-anode voltage in these devices is vertically blocked in the semiconductor, the on-chip isolation between the devices is difficult to achieve. For this reason, the vertical power device is typically employed for high power densities in single-device packages or power modules. In contrast, effective isolation between lateral high-voltage devices can be achieved by using isolation structures, which enables monolithic integration with lateral PiN diodes, transistors, and resistors to achieve control, routing, and power density regulation in smart power-integrated circuits (ICs). This work describes the design and fabrication process of a novel SiC high-voltage lateral PiN (HVLPN) diode with the addition of a lateral isolation structure with a thickness of 10 μm to achieve sufficient isolation between breakdown voltages and devices, as well as a solution for the deep etching of the SiC over 10 μm with a thick enough Hard Mask (HDM), which is required for the actual fabrication process.

There is extensive use of nondestructive test (NDT) inspections on aircraft, and many techniques nowadays exist to inspect failures and cracks in their structures. Moreover, NDT inspections are part of a more general structural health monitoring (SHM) system, where cutting-edge technologies are needed as powerful resources to achieve high performance. The high-performance aspects of SHM systems are response time, power consumption, and usability, which are difficult to achieve because of the system’s complexity. Then, it is even more challenging to develop a real-time low-power SHM system. Today, the ideal process is for structural health information extraction to be completed on the flight; however, the defects and damage are quantitatively made offline and on the ground, and sometimes, the respective procedure test is applied later on the ground, after the flight. For this reason, the present paper introduces an FPGA-based intelligent SHM system that processes Lamb wave signals using piezoelectric sensors to detect, classify, and locate damage in composite structures. The system employs machine learning (ML), specifically support vector machines (SVM), to classify damage while addressing outlier challenges with the Mahalanobis distance during the classification phase. To process the complex Lamb wave signals, the system incorporates well-known signal processing (DSP) techniques, including power spectrum density (PSD), wavelet transform, and Principal Component Analysis (PCA), for noise reduction, feature extraction, and data compression. These techniques enable the system to handle material anisotropy and mitigate the effects of edge reflections and mode conversions. Damage is quantitatively evaluated with classification accuracies of 96.25% for internal defects and 97.5% for external defects, with localization achieved by associating receiver positions with damage occurrence. This robust system is validated through experiments and demonstrates its potential for real-time applications in aerospace composite structures, addressing challenges related to material complexity, outliers, and scalable hardware implementation for larger sensor networks.

In this study, we introduce the impact of gamma irradiation on 4H-SiC based transistor-transistor logic (TTL) inverters. These monolithic bipolar inverters have been successfully demonstrated in a broad spectrum of temperature and supply voltage conditions. In this iteration of experiments, attempts made to the processing to increase beta values. The gamma radiation tests from a ⁶⁰Co source were conducted under various operation conditions and measured in-situ under different biasing conditions. The Silicon Carbide Integrated circuits ( SiC ICs) show excellent tolerance properties to gamma radiation up to doses of nearly 1 MRad. Comparable Si BJT-based TTL inverters show considerable degradation already at one order of magnitude lower doses, clearly demonstrating the superior radiation hardness of 4H-SiC ICs.

In this study, we investigate the impact of Gamma Radiation on 4H Silicon Carbide (SiC) Transistor-Transistor Logic (TTL) integrated circuits (ICs), particularly focusing on inverters processed with distinct types of interface oxides: Thermally Grown, Chemical Vapor Deposition, and Atomic Layer Deposition. This research was conducted using a 60Co source at Hiroshima University, applying varied radiation doses (17.9 rad(Si)/s, 7.3 rad(Si)/s, and 2.47 rad(Si)/s) to assess the resilience of the SiC inverters under these conditions. Our findings reveal that thermal oxides (Batch 1: W1 and W2) demonstrate higher radiation resilience compared to ALD and CVD interface oxides (Batch 2: W3 and W4), attributable to their denser structure and fewer defects. The study also identifies that while the inverters exhibit marginal degradation at gamma doses nearing 700 krad (under 6%), the most critical operational state is the passive mode (VCC = VIN = 0 V), where the build-up of induced charge in the oxide and interface may lead to early IC degradation of the noise margins. The outcomes from this research provide insights into the processing flow and enhancement of SiC electronics. Our results underscore the potential of SiC-based ICs in environments with high radiation levels, such as space missions, nuclear reactors, and medical applications, due to their enhanced radiation tolerance.

Gamma irradiation effects have been investigated on 4H-SiC bipolar junction transistors, where the devices were exposed under different biasing regimes such as saturation, cut-off, active, reverse and zero bias. Since bipolar transistors can be affected by dose rate, three different dose rates were used during irradiation tests. Characterization was performed on the transistors, without irradiation but in-situ to avoid delays between irradiation and characterization. The study explores the relationship between biasing conditions and their impact on radiation-induced degradation of SiC BJT transistors. From these experiments it is clear that 4H-SiC bipolar transistors can withstand high gamma doses, in the worst case less than 22 % degradation of the current gain was seen for doses of up to 2 Mrad(Si).