III-V HBT modeling, scaling and parameter extraction using TRADICA and HICUM Yves Zimmermann, Peter Zampardi, Michael Schroeter

Outline MESA HBTs in TRADICA Parameter extraction Experimental results Future work Summary

Geometry definition in TRADICA - MESA HBT cross section -

Emitter resistance TLM method not suitable different methods for extraction of R E –open collector method (DC) –1/gm method (DC) –calculation from RF-measurements (S-parameter) different emitter sizes needed to get area specific resistance r’ E (including contact and mesa resistance) 1/A E RERE r’ E R E =r’ E /A E +R ACC [r’ E ]=[Ohm um 2 ] R ACC (possible access resistance)

Collector and base-emitter saturation current densities plot log(I) vs. V V BC =0V (Gummel plot) linear fit over linear region gives I S (saturation current) and m (emission coefficient) extract I S and m for transistors with different emitter area average m, calculate J S as current density split J S into an area and a perimeter specific value

Base emitter recombination current density Extract base emitter saturation current first Calculate IBE and subtract it from measured values linear fit over linear region gives I RES (saturation current) and m RE (emission coefficient) extract I RES and m RE for transistors with different emitter area average m RE, calculate J RES as current density Recombination current component

Transit time extraction in HICUM split into two components, τ0 for low-current region, Δτ as high-current correction low current component only depending on V BC, extraction from plot of transit time versus 1/I C in linear region

Gummel characteristics verification (rectangular devices)

Collector current scaling (rectangular devices) Practically no offset, perimeter component very small

Gummel characteristics verification (rectangular devices)

Base emitter current scaling (rectangular devices) Offset indicates perimeter component

Output curves verification (rectangular devices)

Base collector depletion cap. (rectangular devices)

Low current transit time

Importance of accurate measurements THIS IS BAD THIS IS BETTER

Summary General: –HICUM model well suited for modeling DC characteristics –Transit time model in HICUM has to be enhanced (velocity overshoot) –Process variations over wafer seem to be very high Rectangular devices: –Parameters for geometry scaling have been extracted –Modeling of DC characteristics ok –Scaling equations in TRADICA well suited –Model parameter generation with TRADICA possible for low IC applications –Found relatively large bias independent (fringing) BC-capacitance, probably base-metal isolation Ring emitter devices: –CBC does not scale with whole BC area –IC including large perimeter component (ledge working properly???)

Future work Enhancing HICUM transit time equations Implementing ring emitter scaling equations into TRADICA Verification of ring emitter calculations and parameter generation Extraction and verification of high current transit time parameters Library generation for HBT3 rectangular and ring emitter devices Measuring transistors on different DIEs and wafers, and DOEs for estimation of process variations Establishing statistical modeling capability using TRADICA