Modulation of the two-dimensional electron gas channel in flexible AlGaN/GaN high-electron-mobility transistors by mechanical bending

Abstract

We investigate the effect of strain on the two-dimensional electron gas (2DEG) channel in a flexible Al 0.25 Ga 0.75 N/GaN high-electron-mobility transistor (HEMT) by mechanical bending to prove the concept of active polarization engineering to create multifunctional electronic and photonic devices made of flexible group III-nitride thin films. The flexible HEMTs are fabricated by a layer-transfer process and integrated with a 150-lm-thick Cu film. The strain values are estimated from high-resolution x-ray diffraction and Raman spectroscopy in 4-cm bend-down and À4-cm bend-up test conditions. The strain-induced piezoelectric polarization can alter the charge density of the 2DEG in the channel at the AlGaN/GaN interface and thus modify the output characteristics of the flexible HEMTs. Accordingly, output characteristics show an increase in output current by 3.4% in the bend-down condition and a decrease by 4.3% in the bend-up condition. Transfer characteristics show a shift of threshold voltage, which also supports the 2DEG channel modulation during bending. Computational simulation based on the same structure confirms the same current modulation effect and threshold voltage shift. Furthermore, the electrical characteristics of the flexible HEMTs show a repeatable dependence on the strain effect, which offers potential for electro-mechanical device applications.

Novel electromechanical coupling theory of GaN HEMT structure under mechanical clamping

“…This phenomenon can be equivalent to applying a pressure on the gate along the z-axis negative direction. The extra-pressure-induced polarization can enhance the density of 2-DEG and increase the drain current (I D ) in GaN HEMT [28], which is in agreement with the results in both the transfer and output characteristics as disscussed above.…”

Graphite Nanocomposite Substrates for Improved Performance of Flexible, High-Power AlGaN/GaN Electronic Devices

“…4,17,18,27,34,35,42 Other recent reports have demonstrated devices on thin Cu substrates, which act as a heat spreading layer but may pose an issue when incorporated into wearable applications with soft substrates. 36 This work demonstrates the improved performance of the transferrable AlGaN/GaN HEMTs on a thermally conductive polymeric composite substrate without the need for an adhesive layer.…”

“…Carbon-based fillers in polymeric composites are especially promising, as they combine high thermal conductivity with low density. The thermal transport of these carbon-based fillers is highly dependent on the number of atomic layers, decreasing from ∼2000 W m –1 K –1 for graphene to ∼100 W m –1 K –1 for bulk graphite. − However, few studies experimentally demonstrate the impact on flexible electronic device performance, relying on resistive heaters , or rigid commercially available devices, , if demonstrated experimentally at all. − There has been some work regarding the AlGaN/GaN HEMTs transferred to flexible substrates that have inherently poor thermal conductivities and low maximum use temperatures and/or require an adhesive layer that further increases the thermal resistance. ,,,,,, Other recent reports have demonstrated devices on thin Cu substrates, which act as a heat spreading layer but may pose an issue when incorporated into wearable applications with soft substrates . This work demonstrates the improved performance of the transferrable AlGaN/GaN HEMTs on a thermally conductive polymeric composite substrate without the need for an adhesive layer.…”

Skin‐Attached Arrayed Piezoelectric Sensors for Continuous and Safe Monitoring of Oculomotor Movements

“…The single‐crystallinity of the film before and after the film transfer is further confirmed by six sharp peaks located at every 60° in rotational ϕ scan ≈{$${\mathrm{10\bar{1}2}}$$} family of planes (Figure S2c, Supporting Information), corresponding to the sixfold rotational symmetry of the hexagonal‐lattice structure. [ 26 ] The film is aligned in both in‐plane and out‐of‐plane directions, that is, single crystalline. While the single‐crystalline nature without grain boundaries is confirmed, the film contains dislocations from the misfit in lattice constants between the substrate (Si) and film (III‐N).…”