Design and Scaling of SiGe BiCMOS VCOs Above 100GHz S. T. Nicolson1, K.H.K Yau1, K.A. Tang1, P. Chevalier2, A. Chantre2 B. Sautreuil2, and S. P. Voinigescu1 1) Edward S. Rogers Sr. Dept. of Elec. & Comp. Eng., Univ. of Toronto 2) STMicroelectronics

Outline Motivation for W-band SiGe integrated circuits VCO design methodology for low phase noise in W-band Layout considerations Measurement results Conclusions and future work

Motivation for W-band SiGe ICs Typical applications: 77GHz auto radar, 94GHz weather radar, imaging Central to these applications is the low phase noise VCO Process development: NFmin, Rn & Ysopt difficult to measure in W-band Use VCO as a process monitor for the noise performance of SiGe technologies Explore VCO scaling/yield in SiGe Under imaging, mention: security, medical, passive, also mention that applications are few – we need to be creative in finding new ones! We are using the LC-VCO as a process monitor, kind of like the ring oscillator is used.

Add negative Miller capacitors Differential tuning VCO Topology CM VCC LB Cext Cvar Q1 VTUNE+ VTUNE- LEE REE CEE LC VBB 2.5 V No cascode lower phase noise, lower supply voltage Colpitts topology maximize fosc relative to other topologies Augment Cbe with Cext Reduces phase noise Add negative Miller capacitors Increases fosc by cancelling Cm Differential tuning reduces supply induced noise 24mA VTUNE Stress single design and layout, with differing technologies (emitter width and layers). Minimal possible differences between VCOs in vastly different technologies. RB rp cp bib E C B Cext

W-Band VCO Design Methodology Use smallest realizable LB with adequate Q Given fosc, maximize tuning range using large Cext Negative resistance Phase noise formula Phase noise trade-off when HBT pushed to limit Minimize HBT noise  bias at NFmin current density Maximize Vtank and Cext bias at peak fT current density Max. Rneg occurs at peak fT/fMAX bias Since the technologies have the same BEOL, the only tech. dependent design step is finding NFmin bias. This is easily adjusted during testing by means of a DC control voltage.

VCO Fabrication Fabricated in three technology splits: All VCO layouts and bias currents are identical – no redesign Directly compare VCOs fabricated in different processes Use the VCO to optimize HBT profile Noise parameters from phase noise fMAX from VCO output power BiC9 fT = 150GHz fMAX = 160GHz emitter 4×5mm×0.17mm BipX fT = 230GHz fMAX = 300GHz emitter 4×5mm×0.13mm BipX1 fT = 270GHz fMAX = 260GHz emitter 4×5mm×0.13mm Stress single design and layout, with differing technologies (emitter width and layers). Minimal possible differences between VCOs in vastly different technologies.

VCO Layout VCO core area: 100mm × 100mm Spiral inductors where necessary to reduce area Plenty of supply decoupling (MiM and metal-metal) 70mm 100mm

Technology Overview – fT/fMAX Scaling Peak fT/fMAX current density increases at each technology node 0.17mm SiGe JpeakfT = 7mA/mm2 where fT = 150GHz 0.13mm SiGe JpeakfT = 14mA/mm2 where fT = 230GHz (or 250GHz) Contrast with CMOS… JpfT = 0.3mA/mm, JpfMAX = 0.2mA/mm, JNFmin = 0.15mA/mm for 180-65nm nodes Need a plot showning fmax and ft as functions of current density for BiC9, BipX, and BipXF. Make sure that the pfT and pfMAX values agree with the paper and presentation text! fT increase by sqrt(2), JpfT doubles.

Measurement Results VCO performance comparison in 3 SiGe technologies Phase noise performance Temperature testing Wafer mapping

Performance Comparison Across Technology BiCMOS9 MOS var. BiCMOS9 HBT var. BipX HBT var. BipX1 HBT var. Tech. fT/fMAX (GHz) 150/160 230/300 250/260 Differential Pout (dBm) +0.7 -1.3 +2.7 +2.5 SSB PN @ 1MHz (dBc/Hz) -101.6 -80 -98 -101.3 Osc. Freq. (GHz) 96 100 106 104 LC-oscillator frequency insensitive to technology fT/fMAX MOS varactors give less phase noise than HBT (CBC) varactors Higher fMAX  more output power, higher frequency BipX1 results in lowest phase noise State when presenting that this is an issue in CMOS too, because fT and fMAX are so layout dependent. This proves that you have to optimize the transistor layout and metallization for both fT and fMAX.

Phase Noise Performance Oscillation frequency of 104GHz Phase noise of 101.3dBc/Hz @ 1MHz offset Phase Noise in W-Band SiGe VCOs FMCW modulation Averaged Spectral Plot Point out we’re claiming best phase noise, not necessarily best FOM – we’ll talk about that later. **References provided in abstract**

Biasing W-Band VCOs for Low Noise NFmin current density scales with technology and fosc Emitter width JNFmin (scales with JpeakfT) Frequency JNFmin (gets closer to JpeakfT) Noise correlation further increases JNFmin [K. Yau, SiRF, 2006] cp bib C RB E B <inB> <inC> The B and C shot noise currents are correlated Need to say something on this slide about WHY JNFmin goes higher with tech. and freq. How exactly were the NFmin curves generated???????  from measured Y parameters  how is this done? Read Ken’s paper!

Phase Noise Performance Across Bias What is the minimum phase noise current density in W-band VCOs? Measure output power and phase noise w.r.t current density (vary VBB) Looks like phase noise is minimum at peak fT current density phase noise JNFMIN increases with frequency output power CM VCC LB Cext Cvar Q1 VTUNE+ VTUNE- LEE REE CEE LC VBB 2.5 V

W-Band Manufacturability Challenges Manufacturability specifications for automotive radar are stringent Outdoors  wide temperature variations Must last for car’s lifetime Low cost per part requires high yield Is SiGe on the way to meeting such challenges? 25ºC 70ºC 50ºC 125ºC BiC9 MOS var. HBT var. BipX

Wafer Mapping – BiCMOS9 Tested 120 VCOs on 4 wafers Summary of BiC9 VCOs with MOS varactors (60 dice averaged) Summary of BiC9 VCOs with HBT varactors (60 dice averaged) 4 VCOs had significantly below average performance (outliers) 2 of the 4 outlier VCOs failed to oscillate entirely Wafer 1 2 3 4 Center freq. (GHz) 94.7 94.9 95.0 Tuning range (GHz) 4.6 Output power (dBm) 0.2 0.7 0.6 0.8 DC power (mW) 133.8 133.2 137.3 132.6 Wafer 1 2 3 4 Center freq. (GHz) 99.6 100.5 100.1 Tuning range (GHz) 3.4 3.6 3.7 Output power (dBm) -1.1 -1 -1.4 -0.9 DC power (mW) 133.0 136.2 132.8

Wafer Mapping – BipX Oscillation Frequency Phase Noise at 1MHz offset VCO not present Die not tested < -98 dBc/Hz -95 – -98 dBc/Hz -92 – -95 dBc/Hz > -92 dBc/Hz Oscillation Frequency Phase Noise at 1MHz offset 104.5-105.0 GHz 104.0-104.5 GHz 103.5-104.0 GHz 103.0-103.5 GHz Wafer flat Location of VCO in reticule

Figures of Merit Comparison of our work to other state of the art W-Band VCOs References [1] Huang P. et al, ISSCC 2006 [2] Kobayashi K. W. et al, JSSC 1999 [3] Tang K. W. et al. CSICS 2006 [4] Huang P. et al, ISSCC 2006

Conclusions Demonstrated a design methodology for low phase noise in W-Band VCOs Biasing at JpeakfT minimizes phase noise in W-band VCOs Performed a direct comparison of identical VCOs fabricated in different technologies LC-oscillator frequency is insensitive to technology scaling Higher fT technology yielded VCO with lower phase noise Higher fMAX technology yielded VCO with improved output power Future work is required to fully support these conclusions Noise figure measurements in the W-Band (correlate to Y-parameter method) Verify JNFmin in the W-Band and support biasing near JpeakfT for min. phase noise

Technology Overview – fT/fMAX Scaling Improvement in peak fT/fMAX has two contributions Layout  stripe contact, decreased emitter width 0.17mm to 0.13m Vertical profile and processing  doping, materials, epitaxy, etc. How much of the speed improvement is due to each contribution? Measure the 0.13mm HBT layouts fabricated in the 0.17mm process Scaling the emitter width alone doesn’t change current density for peak fT, but does improve speed.