Elsevier

Solid-State Electronics

Volume 129, March 2017, Pages 196-199
Solid-State Electronics

Letter
Performance enhancement of AlGaN/GaN nanochannel omega-FinFET

https://doi.org/10.1016/j.sse.2016.11.005Get rights and content

Highlights

  • AlGaN/GaN omega-FinFETs were fabricated using TMAH wet etching with HfO2 sidewall spacer.

  • The proposed device exhibits excellent performance in both on-state and off-state.

  • This is because the current spreads from the narrow fin to the wide access which supported by the device simulation results.

  • The device shows the excellent gate controllability with completely separated channel region from the GaN buffer.

Abstract

Novel AlGaN/GaN omega-shaped nanochannel FinFETs with fin width of 50 nm were successfully fabricated using TMAH lateral wet etching with ALD HfO2 sidewall spacer. This fin structure apparently exhibited the current spreading in the access region, which results in the suppression of the drain lag effect at high drain voltage and sharp switching performance with subthreshold swing of 57–65 mV/decade. Excellent on- and off-state state performances for the fabricated device prove that the omega-shaped gate structure not only exhibits excellent gate controllability, but also decouples the active nano-channel region from the underlying thick buffer. The proposed device is very promising candidate for high-performance device applications.

Introduction

Recently, AlGaN/GaN-based nanochannel fin-shaped field-effect transistors (FinFETs) have been presented [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. They demonstrated greatly improved on- and off-state performances compared to those of conventional planar AlGaN/GaN heterostructure FETs (HFETs) or metal insulator semiconductor HFETs (MISHFETs). The reason for enhanced device characteristics is due to the excellent electrostatic control of the channel in fully-depleted tri-gate configuration.

Previously, we reported the method of fabricating a 3-dimensional (3D) AlGaN/GaN FinFET with omega-shaped gate geometry [11], realized by using tetramethylammonium hydroxide (TMAH) lateral wet etching and atomic layer-deposited (ALD) HfO2 sidewall spacer. It is expected that the performance of the device can be further improved due to the enhanced gate controllability, because the active region of the device is almost completely separated from the underlying thick GaN buffer layer. The nano-fin structure in Refs. [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12] had a rectangular- or trapezoidal-shaped gate structure; the channel is easily controlled, but still affected by trapping and defects from the GaN buffer layer.

In this work, we analyze the electrical performances of the omega-shaped nanochannel AlGaN/GaN FinFET with fin width of 50 nm and discuss the benefit of the omega-shaped gate structure by comparing the results with those obtained from the conventional AlGaN/GaN MISHFET, fabricated on the same wafer as a reference device.

Section snippets

Structure growth and device fabrication

The epitaxial structure and schematic configuration of the proposed AlGaN/GaN omega-FinFET is shown in Fig. 1(a). The device fabrication process was similar to that described in [11], [12]. Basically, the initially dry etched AlGaN/GaN with trapezoidal shape was laterally etched along 〈1 1 2¯ 0〉 wafer direction in the TMAH solution to form very steep sidewalls [11]. 20 nm-thick ALD HfO2 spacer layer was then deposited on the sidewall surfaces. A second GaN dry etching and lateral wet etching in

Results and discussion

Fig. 2(a) shows the Ids - Vds curves for 36-finger AlGaN/GaN omega-FinFET with nanochannel width of 50 nm and gate length of 2 μm. Despite the complicated fabrication process, the device exhibits excellent output Ids - Vds characteristics with well-defined pinch-off and saturation regions. The on-resistance of the device is as low as 0.19  cm2. The maximum drain current (Id,max) exceeds 0.87 mA, the maximum transconductance (gm,max) is 0.68 mS at Vgs = 1 V and Vds = 10 V. The corresponding normalized I

Conclusions

Novel three-dimensional AlGaN/GaN-based nanochannel fin-shaped field-effect transistor (FinFET) with omega-shaped gate geometry has been fabricated and characterized. The proposed device exhibits excellent performance in both on-state (Id,max of 484 mA/mm, gm,max of 373 mS/mm, and recovery of drain lag, for Lg = 2 μm) and off-state (SS of 57–65 mV/decade, extremely low leakage current of 10−11 mA, very high Ion/Ioff ratio of 1010, much less hysteresis, and remarkable off-state breakdown voltage of ∼220

Acknowledgments

This work was supported by the BK21 Plus funded by the Ministry of Education (21A20131600011), the IT R&D program of MOTIE/KEIT (10048931), and the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (No. 2013R1A6A3A04057719).

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