Thanks to its ultra-high thermal conductivity, diamond has emerged as a key material for overcoming the thermal management bottleneck in high-frequency, high-power chips. Bonding chips directly to a diamond substrate can significantly reduce the near-junction thermal resistance and junction temperature, and is regarded as the ideal solution for thermal management in future high-performance chips and 3D packaging; its application value is attracting increasing attention from the industry.
Resolving the issue of substrate warpage has become a critical step in the application of diamond films for chip bonding.
To address this core bottleneck, Jiang Nan, a researcher at the Ningbo Institute of Materials Technology and Engineering of the Chinese Academy of Sciences, led a team specializing in functional carbon materials to develop an innovative technology that reduces the warpage of diamond films by more than one order of magnitude without compromising film quality, thereby enabling their self-adhesion and self-supporting properties.
With the continued evolution of high-performance computing, high-power communication devices, and 3D packaging technologies, thermal management has become a key bottleneck limiting further improvements in chip performance.
In particular, the high heat flux density generated by third-generation semiconductors such as silicon carbide (SiC) and gallium nitride (GaN), as well as computing chips, during high-power operation has made traditional cooling solutions—which rely on reducing the thermal resistance between the package and the external environment—increasingly unsustainable. An efficient cooling solution that reduces the near-junction thermal resistance by bonding the chip to a highly thermally conductive substrate has become the key to overcoming this challenge.
However, challenges in stress control at the material level—arising from the intrinsic differences in thermal expansion coefficients between diamond and the substrate, as well as issues with the compatibility of nucleation and growth processes—have resulted in excessive warpage in traditional diamond films after substrate removal, making it consistently difficult to meet the stringent requirements for ultra-high substrate flatness in the bonding process.
To address the issue of substrate warpage, the Jiangnan team fabricated a 4-inch self-supporting diamond film with a thickness of less than 100 μm. In its self-supporting state, the warpage of this film is stably controlled within 10 μm, representing a reduction of more than one order of magnitude compared to diamond films produced using conventional processes.
Crucially, this ultra-low warpage endows the film with exceptional flatness, enabling it to exhibit a “self-adhesion” phenomenon whereby it adheres to a glass substrate without the need for external force.
“Typically, only two ultra-flat objects will automatically adhere to each other upon contact. The fact that the diamond film and the glass plate were able to self-adhere indicates that this self-supporting diamond film is extremely flat, with virtually no warpage.”
It is precisely this ultra-flat characteristic in the self-supporting state that enables the diamond film to truly adapt to current chip bonding processes.
At the same time, the ultra-thin, self-supporting structure offers a high degree of flexibility and multidimensional options for packaging design.
This achievement not only paves the way for diamond substrate bonding but also demonstrates its application potential in advanced packaging processes such as heterogeneous integration and 3D stacking.
“The transition of diamond materials from the theoretical value of ultra-high thermal conductivity to practical processes that are mass-producible, packageable, and bondable is becoming a consensus and a goal, and it is also the focal point of competition in next-generation chip thermal management technology.”
