TSMC and ST: strong patent position
"We expect an acceleration of their respective patenting activity on Power GaN-on-Silicon in the next months,” says Remi Comyn from Knowmade
As announced earlier this month, STMicroelectronics will collaborate with Taiwan Semiconductor Manufacturing Corporation (TSMC) in order to accelerate the development of GaN technology for power applications, and more specifically for automotive applications (converters and chargers for hybrid and electric vehicles).
With this recent partnership, STMicroelectronics has joined several other companies using TSMC for volume production of GaN power devices, including GaN Systems, VisIC and Navitas Semiconductor. STMicroelectronics will start by sampling discrete GaN power devices, which will soon be followed by GaN IC products based on TSMC’s GaN-on-Si process technology.
TSMC’s GaN-on-Si technology was reviewed in Knowmade’s 'GaN-on-Si Patent Landscape Analysis' released in January 2020. TSMC holds about 40 patent families related to this technology, which regroup more than 130 patents filed worldwide, mainly in US (70+) and China (25+). “TSMC has leading GaN-on-Silicon manufacturing expertise and we have identified at least 12 key inventions narrowly related to power applications,” says Remi Comyn, technology and patent analyst for compound semiconductors and electronics at Knowmade.
TSMC was actively filing GaN-on-Si patents for power applications between 2012 and 2017 and has strongly focused on the US area (20+ granted patents).The company's patent portfolio protects technological approaches providing improved GaN-on-Si buffer resistivity, using three main approaches: p-type conductivity dopants in graded buffer layers and ungraded buffer layers (patent US 8,791,504); diffusion blocking layer between the buffer layer; and the silicon substrate (patent US 9,245,991); and multi-strained superlattice structures (SLS) to overcome the limitations due to carbon-doping of the buffer layers (patent US 10,109,736).
TSMC has also focused patenting activity on removing the breakdown voltage limitations due to the surface gate-drain region, inserting buried dielectric portions in the AlGaN barrier, in addition to the use of field plate structures and AlGaN barrier with Al-graded compositions (patent US 10,522,532).
According to Knowmade, the latest of TSMC’s GaN-on-Si developments for power applications focused on the fabrication of GaN power integrated circuits (IC) with patent US 9,793,389 related to the isolation of adjacent GaN-on-Si power devices, and US patent 10,522,532 related to the formation of through-GaN vias (TGV).
In its 'GaN-on-Si Patent Landscape Analysis', Knowmade also analysed the patent portfolio of STMicroelectronics, which is still strengthening its IP position in the power GaN patent landscape. In 2017-2018, STMicroelectronics focused on GaN device technology, especially normally-off transistor structures.
STMicroelectronics’ normally-off transistor structures (patents US 10,516,041, US 10,566,450 and US 10,522,646) are based on a tri-layer epitaxial stack NiO/AlGaN/GaN, the selective removal of NiO in the gate region and the deposition of a gate dielectric (AlN, Al2O3 or SiO2) on the AlGaN barrier (with or without recess). The buffer region may include a first carbon-doped buffer layer for increasing the breakdown voltage and a second p-type buffer layer for limiting the degradation of dynamic on-resistance due to the first buffer layer. It can be combined with the presence of a sloped field plate in order to further reduce dynamic on-resistance phenomenon, implemented with the advantageous method described in patent US 10,050,136.
Previously – in 2018 – STMicroelectronics started a joint R&D program with The French Alternative Energies and Atomic Energy Commission (CEA), focused on the development of GaN power devices on 200-mm silicon substrates, in view of establishing a pilot manufacturing line in 2020 in the STMicroelectronics’ foundry located in Tours, France. CEA is a well-established IP player with more than 40 GaN-on-Silicon patents.
Over the last three years, STMicroelectronics has intensified its GaN-on-Silicon patenting activity in the field of power applications with six additional inventions. CEA first focused on enhancement-mode device technology, and then focused on the epi-structures in order to enhance the vertical breakdown voltage. Its recent GaN-on-Si patenting activity also includes an IP collaboration with an automotive player, Renault, regarding power GaN device technology.
“Following the R&D collaboration between STMicroelectronics and CEA since 2018, and the recent announcement of partnership between STMicroelectronics and TSMC, we expect an acceleration of their respective patenting activity on Power GaN-on-Silicon in the next months,” says Remi Comyn from Knowmade.