Thermal Management at the GaN/Diamond Power Device Interface

The demonstration of kilovolt breakdown voltages in gallium nitride (GaN) power devices has long inspired optimization in power electronics and other applications. This is due to the potential for greatly improved conversion efficiency in power systems. GaN devices can be divided into lateral and vertical device structures. In lateral devices, the electric field is aligned laterally in the device and is confined inside the GaN but close to the surface. In vertical devices, the electric field is evenly distributed within the GaN. Therefore, vertical devices can improve the breakdown voltage without increasing the chip size.

Text guide

A major obstacle to realizing the full potential of GaN in both geometries is the device operating temperature. Under operating conditions, the temperature of GaN power devices can exceed 300°C, which reduces electron mobility and thus device efficiency. To reduce the operating temperature of lateral devices, heat-absorbing substrates and coatings have been used, as well as active liquid cooling methods. However, this problem becomes more complicated in vertical geometries because the heat is not generated close to the surface, but in the bulk of the material.

Piontkowski and Luke Yates' team at Sandia National Laboratories have made the latest progress in optimizing the thermal management of diamond and gallium nitride (GaN) electronic devices. The integration of the two materials is achieved by room temperature compression bonding of centimeter-scale GaN and diamond molds through a Ti/Au intermetallic bonding layer. The team used an improved surface activated bonding (SAB) method, which immediately performed Ar fast atom bombardment and then bonding in the same tool under ultra-high vacuum (UHV) conditions.

The buried interface and total bonding area were imaged using transmission electron microscopy (TEM) and confocal acoustic scanning microscopy (C-SAM). Spatially resolved frequency domain thermoreflection (FDTR) revealed that the thermal transport quality of the bond was high, with a thermal boundary conductivity exceeding 100 MW/m2·K. The GaN compressive stress in the well-bonded area was low, less than 80 MPa. This study proposes a new thermal management method to maintain low stress and high thermal boundary conductivity in vertical GaN devices, and the results have been published in ACS Applied Materials & Materials.

Image guide

Figure 1. GaN/diamond device structure and synthesis.

Figure 2. Schematic diagram of an electron microscope.

Figure 3. Thermal reflectivity in the frequency domain.

Figure 4. Raman spectroscopy stress analysis.

Figure 5. Local thermo-mechanical distribution maps: (a) Raman map converted to stress and 18 kHz FDTR map for the thermal part.

曼尼森吉他定制

Thermal Management at the GaN/Diamond Power Device Interface

分享至微信分享

分享至微信