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Developing of Low-resistance Ohmic Contact on GaN HEMTs for High Operating Frequency Applications
Introduction: GaN high-electron-mobility transistors (HEMTs) technology currently offers exceptional device properties for next-generation high power and high frequency applications [1]. This is attributed to their high breakdown voltage and current capabilities. However, the formation of low source/drain contact resistance is required to lower the access resistance and thus enhance DC and RF performance [2].
Research Goal:
Material and Devices:
Analysis & Results:
Conclusion & Future Work: • Development of low ohmic contact resistance with good surface morphology was realized on AlGaN/GaN on LR Si substrate. • Recessed ohmic contacts with lower annealing temperatures could be adopted for better contact resistance Rc.
Abdulaziz BinKhudhayr 2176393, e-mail:[email protected]
University of Glasgow, charity number SC004401
Supervisor Name: Dr.Khaled Elgaid
Figure 2: Schematic diagram of AlGaN/GaN HEMT grown on Si.
Figure 4: Contact resistance for non-recessed & recessed metal stacks.
Figure 4: SEM images of (a) Ti/Al/Mo/Au and (b) Ti/Al/Ni/Au.
Figure 1:Energy Bandgap diagram.
Fabrication Process Material Growth
Two metal schemes with different interlayer metals were utilized for this project:
Table 2:Summary of the development process.
Table 1:Summary of the fabrication process.
Y_Sample A = 4.4354x + 8.4481 Y_Sample B= 4.0199x + 9.7737 Y_Sample C = 4.5482x + 22.694
0
50
100
150
200
0 5 10 15 20 25 30 35
R T, Ω
Gap spacing, µm
Sample A Sample B Sample C
Transfer length method (TLM) was used to characterize ohmic contacts.
Figure 3: Optical microscope image of TLM test structure 150 × 150 µm pads with the spacing 2.5, 5, 10, 15, 20, 25, 30, and 35 µm.
Scanned Electron Microscopy (SEM) of two metal stacks surfaces:
Since non-recessed Ti/Al/Mo/Au metal scheme resulted in the best ohmic contacts, Gate wrap-around d-mode d e v i c e s w e r e fabricated.
Figure 5: devices characteristic.
References: [1] Kolaklieva, L. and Kakanakov, R. (2009). Ohmic Contacts for High Power and High Temperature Microelectronics. Micro Electronic and Mechanical Systems [Accessed 5 Mar. 2015]. [2] U. K. Mishra, L. Shen, T. E. Kazior, and Y.-F. Wu. “GaN-based RF power devices and amplifiers,” Proc. IEEE, vol. 96, no. 2, pp. 287–305, Feb. 2008.