This work exhibits the ability to shift the threshold voltage of an Al0.45Ga0.55N/Al0.3Ga0.7N high electron mobility transistor through the implementation of a 100 nm thick p-Al0.3Ga0.7N gate. A maximum threshold voltage of +0.3 V was achieved with a 3 μm gate length. In addition to achieving enhancement-mode operation, this work also shows the capability to obtain high saturated drain current (>50 mA/mm), no gate hysteresis, high ION,MAX/IOFF,MIN ratio of >109, and exceptionally low gate leakage current of 10-6 mA/mm even under high forward bias of Vgs = 8 V.
The thickening behavior of aluminum scandium nitride (Al0.88Sc0.12N) films grown on Si(111) substrates has been investigated experimentally using X-ray diffraction (XRD), transmission electron microscopy (TEM), atomic force microscopy, and residual stress measurement. Al0.88Sc0.12N films were grown with thicknesses spanning 14 nm to 1.1 um. TEM analysis shows that the argon sputter etch used to remove the native oxide prior to deposition produced an amorphous, oxygen-rich surface, preventing epitaxial growth. XRD analysis of the films show that the A1ScN(002) orientation improves as the films thicken and the XRD A1ScN(002) rocking curve full width half maximum decreases to 1.34 q for the 1.1 pm thick film. XRD analysis shows that the unit cell is expanded in both the a- and c-axes by Sc doping; the a-axis lattice parameter was measured to be 3.172 ± 0.007 A and the c-axis lattice parameter was measured to be 5.000 ± 0.001 A, representing 1.96% and 0.44% expansions over aluminum nitride lattice parameters, respectively. The grain size and roughness increase as the film thickness increases. A stress gradient forms through the film; the residual stress grows more tensile as the film thickens, from -1.24 GPa to +8.5MPa.
This chapter discusses the motivation for the use of Ultra-Wide-Bandgap Aluminum Gallium Nitride semiconductors for power switching and radio-frequency applications. A review of the relevant figures of merit for both vertical and lateral power switching devices, as well as lateral radio-frequency devices, is presented, demonstrating the potential superior performance of these devices relative to Gallium Nitride. Additionally, representative results from the literature for each device type are reviewed, highlighting recent progress as well as areas for further research.
Al-rich AlGaN-channel high electron mobility transistors with 80-nm long gates and 85% (70%) Al in the barrier (channel) were evaluated for RF performance. The dc characteristics include a maximum current of 160 mA/mm with a transconductance of 24 mS/mm, limited by source and drain contacts, and an on/off current ratio of 109. fT of 28.4 GHz and fMAX of 18.5 GHz were determined from small-signal S-parameter measurements. Output power density of 0.38 W/mm was realized at 3 GHz in a power sweep using on-wafer load pull techniques.
Al0.26Ga0.74N/GaN on SiC lateral Schottky diodes were fabricated with variable anode-to-cathode spacing and were analyzed for blocking and on-state device performance. On-chip normally-on High Electron Mobility Transistor (HEMT) structures were also fabricated for a comparison of blocking characteristics. The Schottky diode displayed an ideality factor of 1.59 with a Ni/AlGaN zero bias barrier height of 1.18 eV and a flat band barrier height of 1.59 eV. For anode-to-cathode spacings between 10 and 100 μm, an increase in median breakdown voltages from 529 V to 8519 V and median specific on-resistance (Ron-sp) from 1.5 to 60.7 mΩ cm2 was observed with an increase in spacing. The highest performing diode had a lateral figure of merit of 1.37 GW/cm2 corresponding to a breakdown voltage upwards of 9 kV and a Ron-sp of 59 mΩ cm2. This corresponds to the highest Schottky diode breakdown voltage reported thus far with an Al0.26Ga0.74N/GaN lateral structure.
In this paper, we present heavy ion and proton data on AlGaN highvoltage HEMTs showing Single Event Burnout, Total Ionizing Dose, and Displacement Damage responses. These are the first such data for materials of this type. Two different designs of the epitaxial structure were tested for Single Event Burnout (SEB). The default layout design showed burnout voltages that decreased rapidly with increasing LET, falling to about 25% of nominal breakdown voltage for ions with LET of about 34 MeV·cm2/mg for both structures. Samples of the device structure with lower AlN content were tested with varying gate-drain spacing and revealed an improved robustness to heavy ions, resulting in burnout voltages that did not decrease up to at least 33.9 MeV·cm2/mg. Failure analysis showed there was consistently a point, location random, where gate and drain had been shorted. Oscilloscope traces of terminal voltages and currents during burnout events lend support to the hypothesis that burnout events begin with a heavy ion strike in the vulnerable region between gate and drain. This subsequently initiates a cascade of events resulting in damage that is largely manifested elsewhere in the device. This hypothesis also suggests a path for greatly improving the susceptibility to SEB as development of this technology goes forward. Lastly, testing with 2.5 MeV protons showed only minor changes in device characteristics.
In this paper we describe a method for controlling both the residual stress and the through-thickness stress gradient of aluminum nitride (AlN) thin films using a multi-step deposition process that varies the applied radio frequency (RF) substrate bias. The relationship between the applied RF substrate bias and the AlN residual stress is characterized using AlN films grown on oxidized silicon substrates is determined using 100 nm-1.5 μm thick blanket AlN films that are deposited with 60-100 W applied RF biases; the stress-bias relationship is found to be well described using a power law relationship. Using this relationship, we develop a model for varying the RF bias in a series of discrete deposition steps such that each deposition step has zero average stress. The applied RF bias power in these steps is tailored to produce AlN films that have minimized both the residual stress and the film stress gradient. AlN cantilevers were patterned from films deposited using this technique, which show reduced curvature compared to those deposited using a single RF bias setting, indicating a reduction of the stress gradient in the films.