Molecular and Nanoelectronics Group


Figure 1—3-D model and SEM picture of the 1x5 µm2 InAlAs/InGaAs/InAlAs DHBT fabricated at The University of Manchester [1]

            The explosive growth of low-power, high speed digital applications with data rates exceeding 40Gbps, broadband WLAN at 60 GHz and automotive radar systems at 77GHz  and other applications as shown in Figure 2 require devices with cut-off (fT) and maximum oscillation frequencies (fmax) much higher than 100 GHz.  Even higher frequencies are required for sub-mm wave (300 GHz to 1THz) applications in imaging, radio astronomy, and spectroscopy [2].
The advantage of Indium Phosphide (InP) based Heterojunction Bipolar Transistors (HBTs) over Bipolar Junction Transistors (BJTs), Complementary Metal Oxide Semiconductor (CMOS), SiGe HBTs and InP based High Electron Mobility Transistors (HEMTs) lies in such ultra-high speed mixed- signal and microwave power applications. InP based HBTs operate at cut off frequency (fT) of ~ 450 GHz at 0.5μm lithographic feature size with a high breakdown voltage of 5V [2]. This excellent performance is due to a combination of favorable material properties like very high electron mobility and saturation velocity, very low surface recombination velocity and higher thermal conductivity.
In order to take full advantage of these material properties, equally smart device design is required. The device optimization is in general a twofold process comprising epitaxial and geometrical optimization. This requires deep understanding of the physical processes responsible for the carrier transport which culminates in very favorable terminal device characteristics.

Figure 2 — Frequency bands for high-speed digital and mixed signal applications [3]

 

References:

[1]        M. Mohiuddin, "InGaAs/InAlAs DHBT for high-speed, low-power digital applications," in Faculty of Engineering and Physical Sciences, vol. PhD. Manhcester: The University of Manchester, 2010, pp. 259.

[2]        M. Rodwell, E. Lobisser, M. Wistey, V. Jain, A. Baraskar, E. Lind, J. Koo, Z. Griffith, J. Hacker, M. Urteaga, D. Mensa, R. Pierson, and B. Brar, "THz Bipolar Transistor Circuits: Technical Feasibility, Technology Development, Integrated Circuit Results," 2008 Ieee Csic Symposium, pp. 1-3, 2008.

[3]        J. D. Cressler, "Emerging Application Opportunities for SiGe Technology," presented at IEEE Custom Integrated Circuits Conference, San Jose, CA, 2008.