Ultrafast operation of heterostructure bipolar transistors resulting from coherent base transport of minority carriers

Transistor Action by Transit Time Phase Shift - a Study for SiGe Based Devices

“…For a graded band-gap HBT Luryi et al. [7] have derived the following expression for the base transport factor er a3 = cosh(A) + (1 + 2 ico rB,drift / r)2 sinh(Q) (3) where i= r2 + 2ictrB,diff and r is the ratio of the diffusion time T,Bdiff = WB /2Db to the drift time tB,drift = WB / v . Assuming for simplicity COTE << I the output resistance becomes [9] R OS(-P) -COS((P +e)||R Inserting eq.…”

“…Certainly, there is a frequency limit and one may ask which Si based heterojunction device concepts will be suited to open frequency ranges above that accessible by SiGe HBT technology. One of those concepts may be the extension of the active operation of bipolar transistors to frequencies beyond the cut-off frequencies by using transit-time phase shifts which can result in a negative output resistance of the transistor [3]. Such phase shifts exist in any fmiite sized device.…”