Over 450-GHz f_t and f_max InP/InGaAs DHBTs With a Passivation Ledge Fabricated by Utilizing SiN/SiO₂ Sidewall Spacers

Abstract

This paper describes InP/InGaAs double heterojunction bipolar transistor (HBT) technology that uses SiN/SiO 2 sidewall spacers. This technology enables the formation of ledge passivation and narrow base metals by i-line lithography. With this process, HBTs with various emitter sizes and emitterbase (EB) spacings can be fabricated on the same wafer. The impact of the emitter size and EB spacing on the current gain and high-frequency characteristics is investigated. The reduction of the current gain is <5% even though the emitter width decreases from 0.5 to 0.25 µm. A high current gain of over 40 is maintained even for a 0.25-µm emitter HBT. The HBTs with emitter widths ranging from 0.25 to 0.5 µm also provide peak f t of over 430 GHz. On the other hand, peak f max greatly increases from 330 to 464 GHz with decreasing emitter width from 0.5 to 0.25 µm. These results indicate that the 0.25-µm emitter HBT with the ledge passivaiton exhibits balanced highfrequency performance (f t = 452 GHz and f max = 464 GHz), while maintaining a current gain of over 40.

High-performance compound-semiconductor integrated circuits for advanced digital coherent optical communications systems

“…Low-permittivity benzocyclobutene (BCB) was used as the isolating layer between the interconnections. In addition, we recently developed 0.25-µm-emitter-width InP HBT technology [42]. The fabricated 0.25-µm HBTs exhibit current gain of over 30 and f t =f max of over 400/450 GHz at Jc of 10 mA/µm 2 , as shown in Fig.…”

Composition- and Doping-Graded-Base InP/InGaAsSb Double Heterojunction Bipolar Transistors Exhibiting Simultaneous <inline-formula> <tex-math notation="TeX">\(f_{t}\) </tex-math></inline-formula> and <inline-formula> <tex-math notation="TeX">\(f_{\textrm {max}}\) </tex-math></inline-formula> of Over 500 GHz

“…formed as the same as our baseline DHBTs [10]. First, tungsten-based emitter metals were deposited on the n + -InGaAs emitter contact.…”

“…The ideality factors of the base and collector currents are 1.80 and 1.03, respectively. The ideality factor of the base current is large, which is due to the narrow emitter-base spacing (∼0.05 μm) [10]. Fig.…”

InP/InGaAs double heterojunction bipolar transistors with BV CEO = 12 V and f max = 470 GHz

“…InP/InGaAs DHBT fabrication: DHBTs were fabricated by utilising SiN/SiO 2 sidewall spacers with i-line lithography [3]. First, a tungstenbased metal was deposited on the InGaAs emitter contact.…”

“…Here, the external base surface was passivated with the InP emitter (ledge layer). The ledge layer is very effective in reducing the base surface recombination current because it suppresses electron injection into the surface of the external base by providing an additional potential barrier [3]. Following the formation of the base metals by a lift-off technique with SiN/SiO 2 sidewall spacers, the base-collector mesas and emitter and collector metals were formed.…”