Thermal stress modelling of diamond on GaN/III-Nitride membranes

Abstract

Diamond heat-spreaders for gallium nitride (GaN) devices currently depend upon a robust wafer bonding process. Bonding-free membrane methods demonstrate potential, however, chemical vapour deposition (CVD) of diamond directly onto a III-nitride (III-N) heterostructure membrane induces significant thermal stresses. In this work, these thermal stresses are investigated using an analytical approach, a numerical model and experimental validation. The thermal stresses are

Diamond/GaN HEMTs: Where from and Where to?

“…At the same time the bottleneck of the heat extraction was recognized to be the TBR between GaN and diamond (TBR GaN/diamond ) [72] and most of following research focused on decreasing it, whether by decreasing the dielectric thickness, by using a different dielectric, or by optimizing the diamond nucleation layer [10,[72][73][74][75][76][77][78][79][80][81][82][83][84]. The impact of the thickness of the GaN buffer layer on the R th of the HEMT devices [85][86][87][88][89][90] and the effects of the stress caused by the difference in the CTEs of GaN and diamond [91][92][93][94][95][96] were also evaluated by different research groups. A more detailed description and discussion of the main findings is included in Section 4.1.…”

“…This approach presents no technological barrier to the incorporation of an AlN "initiation" layer into the GaN buffer close to the device channel; however, due to the low thickness of the GaN membranes and the simultaneously high temperatures required for diamond growth, the bowing of the membranes during the diamond deposition step cannot be neglected. This phenomenon was recently analyzed in detail in [95] using commercial GaN-on-Si wafers as the starting material. The processing steps are described in Figure 19a.…”

Diamond as the heat spreader for the thermal dissipation of GaN-based electronic devices

“…Except for the lattice mismatch between the film and substrate, the thermal stress is also a well-known challenge. The thermal stresses arise due to the thermomechanical properties of the layers in the stack [35], the differences in the thermal expansion coefficients. The stresses bowed and/or warped the wafers as they cooled down from the process temperature to room temperature.…”

“…A decreasing diamond thermal resistance with increasing growth temperature was also observed. To compensate the thermal stress between GaN and diamond during the epitaxial growth, Cuenca and Smith proposed a membrane-based technology [35,82]. From their analysis based on the analytical models, the bow for a membrane structure with small sizes were underestimated and the bow could be reduced if the membrane was pre-stressed to become flat at CVD temperatures.…”

Nucleation of diamond films on heterogeneous substrates: a review

“…The thick diamond layer peeled off immediately aer growth. The most probable reason is the stress induced by the thermal mismatch between substrate and diamond lm as the growth happens at an elevated temperature of 800 C. 97 When the seed density is lower, voids were created in the initial layers of diamond. These void layers may have resulted in reliving some of the stress in the lm.…”