Ultra-Low Resistance Base Ohmic Contact with Pt/Ti/Pt/Au for High-f_max AlGaAs/GaAs Heterojunction Bipolar Transistors

Abstract

Ohmic contacts to 500-Å-thick p-Al0.1Ga0.9As layer formed with a Pt/Ti/Pt/Au metal system were investigated. An extremely low contact resistivity of 4.2×10-7 Ω ·cm2 was obtained. The contact resistance increased with the increment of the Pt thickness, because the thicker the intermetallic layer becomes the thinner the AlGaAs layer beneath it, which leads to a higher contact resistance. The optimum Pt thickness was around 50 Å. Moreover, this metal scheme was thermally stable at 350° C. A high f max of 160 GHz was obtained for AlGaAs/GaAs HBTs using Pt/Ti/Pt/Au base electrodes. A multiplexer (MUX) lC implemented with these high-f max HBTs operated properly up to 40 Gbps, the highest speed ever reported. This value was restricted by the measuring instrument capability.

Optimization of the base electrode for InGaAs/InP DHBT structures with a buried emitter-base junction

“…These particular metals were chosen, since they are commonly used for ohmic contacts in III-V materials. [2][3][4][5][6] Pt and Ti tend to have a fairly smooth diffusion profile when annealed at our maximum processing temperature of 300°C. [2][3][4] Although Pd and Au have rougher diffusion profiles, some work has indicated that if they are thin enough, they may also be used.…”

“…[2][3][4][5][6] Pt and Ti tend to have a fairly smooth diffusion profile when annealed at our maximum processing temperature of 300°C. [2][3][4] Although Pd and Au have rougher diffusion profiles, some work has indicated that if they are thin enough, they may also be used. 5 Furthermore, Pt is an excellent diffusion barrier to Au at our processing temperature of 300°C, provided it is thick enough to avoid pinholes or other defects, so Au can be used as the top metal for all of the subsequent interconnects.…”

A 40 GHz D-type flip-flop using AlGaAs/GaAs HBTs

“…An InGaAs layer was adopted as a cap layer to reduce the emitter contact resistance. By using Pt/Ti/Pt/Au base metal, low contact resistivity of 8 x 10-7 Clcm2 was obtained [6]. Figure 1 shows the RF performance of the HBT.…”