Gallium nitride (GaN) is a wide bandgap semiconductor with a high field breakdown and the capability to operate at high temperatures and high switching frequencies, which would normally lead to field breakdown in silicon. Additionally, GaN-based heterostructures (e.g., AlGaN/GaN) have a high carrier mobility two-dimensional electron gas (2DEG). These properties make GaN-based devices ideal for applications which require high power density, such as electric vehicles. Additionally, there has been increasing development in wide bandgap technologies, especially in sensors that have current-sensing capabilities in addition to their main function. This enables one to place sensors directly on an object of interest, such as a motor, and be able to monitor for instances such as large current draws, which can lead to failure in systems.

Typically, GaN device reliability is tested through means such as a High Temperature Storage (HTS) test, and further characterized through current-voltage measurements and charge carrier measurements. The different material stacks used in GaN device contacts, as well as variation in the GaN substrates themselves, can cause reliability concerns such as interdiffusion at different temperature ranges. While one set of HTS tests may have little change on one GaN-based substrate and contact species, another GaN-based substrate with a different contact stack may fail sooner or at a lower temperature. Here, we investigate the reliability of GaN-based Hall Effect sensors using HTS tests to accelerate device failure. To demonstrate the reliability of these devices, current-voltage (I-V) electrical measurements, HTS tests, Scanning Electron Microscope (SEM) imaging with Energy Dispersive X-Ray Spectroscopy (EDX), and X-Ray Photoelectronic Spectroscopy (XPS) were used to determine failure modes and mechanisms. The set of HTS tests used involved different temperatures (200°C, 350°C, 450°C, and 600°C) in air as well as inert environments. Electrical measurements quantified the change in resistance values over time and were used to calculate the activation energy of the degradation process and predicted failure times. Complimentary to this, XPS survey scans and elemental analysis were used to identify surface diffusion of the device contact stacks. Finally, SEM and EDX imaging were used to determine the evolution of surface morphology and diffusion locations in the contacts, as well as further validate XPS results. Preliminary results suggest gold interdiffusion in contact metallization stacks, leading to electrical degradation observations in I-V characterization. Additionally, XPS spectra suggested the presence of gallium on contacts, which could lead to 2DEG degradation. Finally, a strong reliance on the geometry of the sensor active region, as well as ohmic contact size was found for overall reliability. It was found that devices with smaller ohmic contacts appeared to have increasingly higher resistance values for each temperature and timestep, as compared to devices which contained larger contacts.


Degradation of Gallium Nitride-Based Hall Effect Sensors in High Temperature Environments

Division / Sponsors: 
Electronic & Photonic Packaging Division (EPPD)

Paper Proceedings: https://asmedigitalcollection.asme.org/InterPACK/InterPACK2020/volume/84041

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