M. Fjer

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Publications (2)2.32 Total impact

  • Article: Strained-Silicon Heterojunction Bipolar Transistor
    S. Persson, M. Fjer, E. Escobedo-Cousin, S.H. Olsen, B.G. Malm, Yong-Bin Wang, P.-E. Hellström, M. Östling, A.G. O'Neill
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    ABSTRACT: Experimental and modeling results are reported for high-performance strained-silicon heterojunction bipolar transistors (HBTs), comprising a tensile strained-Si emitter and a compressively strained Si<sub>0.7</sub>Ge<sub>0.3</sub> base on top of a relaxed Si<sub>0.85</sub>Ge<sub>0.15</sub> collector. By using a Si<sub>0.85</sub>Ge<sub>0.15</sub> virtual substrate strain platform, it is possible to utilize a greater difference in energy band gaps between the base and the emitter without strain relaxation of the base layer. This leads to much higher gain, which can be traded off against lower base resistance. There is an improvement in the current gain β of 27 × over a conventional silicon bipolar transistor and 11× over a conventional SiGe HBT, which were processed as reference devices. The gain improvement is largely attributed to the difference in energy band gap between the emitter and the base, but the conduction band offset between the base and the collector is also important for the collector current level.
    IEEE Transactions on Electron Devices 07/2010; · 2.32 Impact Factor
  • Conference Proceeding: Fabrication and characterisation of strained Si heterojunction bipolar transistors on virtual substrates
    S. Persson, M. Fjer, E. Escobedo-Cousin, G. Malm, Y.-B. Wang, P.-E. Hellstrom, M. Ostling, E.H.C. Parker, L.J. Nash, P. Majhi, S.H. Olsen, A.G. O'Neill
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    ABSTRACT: Strained Si HBTs have been demonstrated for the first time with a maximum current gain (beta) of 3700 using a relaxed Si<sub>0.85</sub>Ge<sub>0.15</sub> virtual substrate, Si<sub>0.7</sub>Ge<sub>0.3</sub> base and strained Si emitter. This represents 10times and 27times larger gain compared with pseudomorphic SiGe HBTs and Si control BJTs which were manufactured in parallel and had current gains of 334 and 135, respectively. The strained Si HBTs exhibited satisfactory breakdown voltage (2.5 V) compared with SiGe HBTs (2.7 V) and Si BJTs (4.5 V) and excellent control of collector off-state leakage (< 20 fA).
    Electron Devices Meeting, 2008. IEDM 2008. IEEE International; 01/2009
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