Only a few years ago, an account of degradation of silicon carbide high-voltage p-i-n diodes was presented at the European Conference on Silicon Carbide and Related Compounds (Kloster Banz, Germany, 2000). This report was followed by the intense effort of multiple groups utilizing varied approaches and subsequent progress in both fundamental understanding of this phenomenon and its elimination. The degradation of SiC p-i-n junctions is now well documented to be due to the expansion of Shockley-type stacking faults in the part of the devices reached by the electron-hole plasma. The faults can gradually cover most of the junction area, impeding current flow and, as a result, increasing the on-state resistance. While in most semiconductors stacking faults are electrically inactive, in hexagonal silicon carbide polytypes (4H- and 6H-SiC) they form quantum-well-like electron states observed in luminescence and confirmed by first-principles calculations. The stacking-fault expansion occurs via motion of 30° sil...

Degradation of hexagonal silicon-carbide-based bipolar devices

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Materials Science Forum

Mechanical properties of nano-silver joints as die attach materials

In order to take the full advantage of the high-temperature SiC and GaN operating devices, package materials able to withstand high-temperature storage and large thermal cycles have been investigated. The temperature under consideration here are higher than 200 °C. Such temperatures are required for several potential applications such as down-hole oil and gas industry for well logging, aircrafts, automotive, and space exploration. This review focuses on the reliability of a selection of potential components or materials used in the package assembly as the substrates, the die attaches, the interconnections, and the encapsulation materials. It reveals that, substrates with low coefficient of thermal expansion (CTE) conductors or with higher fracture resistant ceramics are potential candidates for high temperatures. Die attaches and interconnections reliable solutions are also available with the use of compatible metallization schemes. At this level, the reliability can also be improved by reducing the CTE mismatch between assembled materials. The encapsulation remains the most limiting packaging component since hard materials present thermomechanical reliability issues, while soft materials have low degradation temperatures. The review allows identifying reliable components and materials for high-temperature wide bandgap semiconductors and is expected to be very useful for researchers working for the development on high-temperature electronics.

Survey of High-Temperature Reliability of Power Electronics Packaging Components

Silver (Ag) has been under development for use as interconnect material for power electronics packaging since the late 1980s. Despite its long development history, high thermal and electrical conductivities, and lead-free composition, sintered Ag technology has limited market penetration. This review sets out to explore what is required to make this technology more viable. This review also covers the origin of sintered Ag, the different types and application methods of sintered Ag pastes and laminates, and the long-term reliability of sintered Ag joints. Sintered Ag pastes are classified according to whether pressure is required for sintering and further classified according to their filler sizes. This review discusses the main methods of applying Ag pastes/laminates as die-attach materials and the related processing conditions. The long-term reliability of sintered Ag joints depends on the density of the sintered joint, selection of metallization or plating schemes, types of substrates, substrate roughness, formulation of Ag pastes/laminates, joint configurations (i.e., joint thicknesses and die sizes), and testing conditions. This paper identifies four challenges that must be overcome for the proliferation of sintered Ag technology: changes in materials formulation, the successful navigation of the complex patent landscape, the availability of production and inspection equipment, and the health concerns of Ag nanoparticles. This paper is expected to be useful to materials suppliers and semiconductor companies that are considering this technology for their future packages.

/pdf/are-sintered-silver-joints-ready-for-use-as-interconnect-2rnz0z0bm7.pdf

Are Sintered Silver Joints Ready for Use as Interconnect Material in Microelectronic Packaging

High temperature power electronics has become possible with the recent availability of silicon carbide devices. This material, as other wide-bandgap semiconductors, can operate at temperatures above 500 °C, whereas silicon is limited to 150-200 °C. Applications such as transportation or a deep oil and gas wells drilling can benefit. A few converters operating above 200 °C have been demonstrated, but work is still ongoing to design and build a power system able to operate in harsh environment (high temperature and deep thermal cycling).

/pdf/state-of-the-art-of-high-temperature-power-electronics-3qyx36fnso.pdf

State of the art of high temperature power electronics

Extractions of barrier heights of 6H and 4H-SiC Schottky diodes have been performed on structures with various gate metallization, using both capacitance-voltage (C-V) and current-voltage (I-V) measurements. The sum of the two barriers extracted by C-V measurements on both n-type and p-type materials is found to be higher than the band gap energy E-G, whereas the one extracted by I-V is less than E-G. However, above room temperature, temperature variations of barrier heights are in agreement with the variations of E-G. We have also computed theoretical I-V characteristics using a two-barrier height model. By taking account of temperature variations of a large number of parameters, e.g., the carrier mobility, free carrier concentration, and barrier height, we have achieved a good fit with experimental data. The model is shown to be valid for n-type Schottky diodes over a wide range of temperatures (from 100 to 500 K).

Barrier height determination of SiC Schottky diodes by capacitance and current-voltage measurements

https://hal.archives-ouvertes.fr/hal-03305997/document

Deep SiC etching with RIE

The formation of low resistivity ohmic contacts to p-type 4H–SiC is achieved. Transfer length method (TLM)-based structures were fabricated on 0.8 µm thick epitaxial p-type silicon carbide (4H–SiC) layers. TLM metal patterns were obtained by a lift-off procedure and electron beam deposition of Ni, Ti and Al. The electrical properties of the contacts were examined using current/voltage measurements. Contact resistivity as a function of annealing was investigated over the temperature range from 700 to 1000 °C. The lowest contact resistivity of 1.5 × 10−5 Ω cm2 was obtained for the Ni/Ti/Al/Ni contact after annealing at 800 °C for 90 s. Using secondary ion mass spectrometry, energy-dispersive x-ray spectroscopy and x-ray diffraction measurements, we quantitatively and qualitatively determined the formation and the nature of the ohmic contact to p-type SiC.

/pdf/the-role-of-nickel-and-titanium-in-the-formation-of-ohmic-201bpbn5sf.pdf

Mihai Lazar

Papers

State of the art of high temperature power electronics

Barrier height determination of SiC Schottky diodes by capacitance and current-voltage measurements

Deep SiC etching with RIE

The role of nickel and titanium in the formation of ohmic contacts on p-type 4H?SiC

Experimental determination of impact ionization coefficients in 4H-SiC