Ultra high-speed 0.25-/spl mu/m emitter InP-InGaAs SHBTs with f/sub max/ of 687 GHz

We have developed novel but simple process techniques for high speed InP SHBTs. For parasitic reduction, the collector layer is undercut using an etch-stop layer, the base pad is isolated, and the emitter metal is widened using thick plated gold. For transit time reduction, the SHBT employs InGaAs base with graded In-composition and InGaAlAs emitter setback with graded Al-composition. Maximum extrapolated f/sub max/ of about 687 GHz with f/sub T/ of 215 GHz is achieved for 0.25 /spl times/ 8 /spl mu/m/sup 2/ emitter area devices at I/sub c/ = 8 mA and V/sub ce/ = 15 V. This data clearly shows that the optimized conventional process can offer direct implementation of InP HBT for high-speed electronic circuit fabrication.