With increasing amount of user data and applications in wireless communication technology, demands are growing on performance and fabrication costs. One way to decrease cost is to integrate the building blocks in an RF system where digital blocks and high power amplifiers then are combined on one chip. This thesis presents LDMOS transistors integrated in a 65 nm CMOS process without adding extra process steps or masks. High power performance of the LDMOS is demonstrated for an integrated WLAN-PA design at 2.45 GHz with 32.8 dBm output power and measurements also showed that high output power is achievable at 5.8 GHz. For the first time, this kind of device is moreover demonstrated at X-band with over 300 mW/mm output power, targeting communication and radar systems at 8 GHz. As SOI is increasing in popularity due to better device performance and RF benefits, the buried oxide can cause thermal problems, especially for high power devices. To deal with self-heating effects and decrease the RF substrate losses further, this thesis presents a hybrid substrate consisting of silicon on top of polycrystalline silicon carbide (Si-on-poly-SiC). This hybrid substrate utilizes the high thermal conductivity of poly-SiC to reduce device self-heating and the semi-insulating properties to reduce RF losses. Hybrid substrates were successfully fabricated for the first time in 150 mm wafer size by wafer bonding and evaluation was performed in terms of both electrical and thermal measurements and compared to a SOI reference. Successful LDMOS transistors were fabricated for the first time on this type of hybrid substrate where no degradation in electrical performance was seen comparing the LDMOS to identical transistors on the SOI reference. Measurements on calibrated resistors showed that the thermal conductivity was 2.5 times better for the hybrid substrate compared to the SOI substrate. Moreover, RF performance of the hybrid substrate was investigated and the semi-insulating property of poly-SiC showed to be beneficial in achieving a high equivalent substrate parallel resistance and thereby low substrate losses. In a transistor this would be equal to better efficiency and output power. In terms of integration, the hybrid substrate also opens up the possibility of heterogeneous integration where silicon devices and GaN devices can be fabricated on the same chip.

In this thesis, we are making a new approach to fabricate silicon on insulator (SOI). By replacing the buried silicon dioxide and the silicon handling wafer with silicon carbide through hydrophilic wafer bonding, we have achieved silicon on crystalline silicon carbide for the first time and silicon on polycrystalline silicon carbide substrates at 150 mm wafer size. The conditions for the wafer bonding are studied and the surface and bond interface are characterized. Stress free and interfacial defect free hybrid wafer bonding has been achieved. The thermally unfavourable interfacial oxide that originates from the hydrophilic treatment has been removed through high temperature annealing, denoted as Ox-away. Based on the experimental observations, a model to explain the dynamics of this process has been proposed. Ox-away together with spheroidization are found to be the responsible theories for the behaviour. The activation energy for this process is estimated as 6.4 eV. Wafer bonding of Si and polycrystalline SiC has been realised by an intermediate layer of amorphous Si. This layer recrystallizes to some extent during heat treatment. Electronic and thermal testing structures have been fabricated on the 150 mm silicon on polycrystalline silicon carbide hybrid substrate and on the SOI reference substrate. It is shown that our hybrid substrates have similar or improved electrical performance and 2.5 times better thermal conductivity than their SOI counterpart. 2D simulations together with the experimental measurements have been carried out to extract the thermal conductivity of polycrystalline silicon carbide as κpSiC = 2.7 WK-1cm-1. The realised Si-on-SiC hybrid wafer has been shown to be thermally and electrically superior to conventional SOI and opens up for hybrid integration of silicon and wide band gap material as SiC and GaN.