Integration of RF Circuits with High Speed GaN Switching on Silicon Substrates

Lead Research Organisation: University of Cambridge
Department Name: Materials Science & Metallurgy


Future generation (5G) mobile phones and other portable devices will need to transfer data at a much higher rate than at present in order to accommodate an increase in the number of users, the employment of multi-band and multi-channel operation, the projected dramatic increase in wireless information exchange such as with high definition video and the large increase in connectivity where many devices will be connected to other devices (called "The Internet of Things"). This places big challenges on the performance of base stations in terms of fidelity of the signal and improved energy efficiency since energy usage could increase in line with the amount of data transfer. To meet the predicted massive increase in capacity there will be a reduced reliance on large coverage base-stations, with small-cell base-stations (operating at lower power levels) becoming much more common. In addition to the challenges mentioned above, small cells will demand a larger number of low cost systems.

To meet these challenges this proposal aims to use electronic devices made from gallium nitride (GaN) which has the desirable property of being able to operate at very high frequencies (for high data transfer rates) and in a very efficient manner to reduce the projected energy usage. To maintain the high frequency capability of these devices, circuits will be integrated into a single circuit to reduce the slowing effects of stray inductances and capacitances. Additionally these integrated circuits will be manufactured on large area silicon substrates which will reduce the system unit cost significantly.

The proposed high levels of integration using GaN devices as the basic building block and combining microwave and switching technologies have never been attempted before and requires a multi-disciplinary team with complementary specialist expertise. The proposed consortium brings together the leading UK groups with expertise in GaN crystal growth (Cambridge), device design and fabrication (Sheffield), high frequency circuit design and fabrication (Glasgow), variable power supply design (Manchester) and high frequency characterisation and power amplifier design (Cardiff). Before designing and developing the technology for fabricating the integrated systems to demonstrate the viability of the proposed solutions, a deep scientific understanding is required into how the quality of the GaN crystals on silicon substrates affect the operation of the devices. In summary, the powerful grouping within the project will bring together the expertise to design and produce the novel integrated circuits and systems to meet the demanding objectives of this research proposal.
Description The work on the growth of nitride high electron mobility transistors on silicon during this award has greatly enhanced our understanding of the mechanisms controlling strain in such devices. This will help us, in future, to develop growth methods which allow the wafer to remain flat (which is important for wafer processing) whilst growing thick layers which tend to introduce strain into the system and bow it into a non-flat shape. We have also increased understanding of the mechanisms which control the film and the substrate conductivity post-growth, which is vital to aid understanding of the device electrical performance.
Exploitation Route The robust growth methods we are developing may be adopted by our industrial partners for commercial devices. Materials grown by these methods are also broadly available to the UK community via the EPSRC National Epitaxy Facility.
Sectors Digital/Communication/Information Technologies (including Software),Electronics