NTU GIEE NanoSiOE 1 Strain-enhanced Device and Circuit for Optical Communication System 指導教授：劉致為 博士 學生：余名薪 台灣大學電子工程學研究所

NTU GIEE NanoSiOE 2 Outline  Introduction  Optical Communication System  Mechanical/Package Strain Technique  Strain-enhanced MOS Photodetector  Strain-enhanced Transimpedance Amplifier  7Gb/s Transimpedance Amplifier  SiGe HBT BiCMOS Active Inductor  Summary and Future Work

NTU GIEE NanoSiOE 3 Optical Communication System Photodetector & Transimpedance Amplifier (TIA) System block diagram Transmitter Receiver Medium

NTU GIEE NanoSiOE 4 Mechanical/Package Strain Technique Side viewTop view Mechanical setup (detector) Biaxial Tensile Strain Uniaxial Tensile Strain

NTU GIEE NanoSiOE 5 Mechanical/Package Strain Technique Mechanical setup (circuit chip) Biaxial Tensile Strain Uniaxial Tensile Strain

NTU GIEE NanoSiOE 6 Ramam & Electroluminescence spectra Ramam spectrumEL spectrum The red-shift of Si-Si peak in Ramam spectra indicates 0.13% biaxial tensile strain and 0.35% uniaxial tensile strain. The EL spectra of a MOS LED under tensile strain indicates bandgap shrinkage. Mechanical/Package Strain Technique

NTU GIEE NanoSiOE 7 Mechanical/Package Strain Technique Current change (%) At |V GS |-|V T |=1V 250nm node (L=240nm) Compressive 0.06% strain Tensile 0.06% strain NFET Uniaxial // channel Uniaxial ┴ channel Biaxial PFET Uniaxial // channel Uniaxial ┴ channel Biaxial Current enhancement in MOSFET The drain current is enhanced owing to the electron mobility enhancement. NFET has enhancement under tensile strain, and PFET has enhancement under uniaxial compressive strain parallel to channel and the uniaxial tensile strain perpendicular to channel.

NTU GIEE NanoSiOE 8 Outline  Introduction  Strain-enhanced MOS Photodetector  Metal/Thin-oxide/P-Si Tunneling Diode Photodetector  Responsivity Enhancement by Tensile Strain  Strain-enhanced Transimpedance Amplifier  7Gb/s Transimpedance Amplifier  SiGe HBT BiCMOS Active Inductor  Summary and Future Work

NTU GIEE NanoSiOE 9 MOS Tunneling Diode Photodetector I-V & C-V characteristics I-V curveC-V curve At the negative bias region, the device can serve as a LED. When the gate is biased at the positive voltage greater than threshold voltage, the device can serve as a PD. C-V indicates that the deep depletion in the NMOS tunneling diode is formed for the large positive gate bias.

NTU GIEE NanoSiOE 10 MOS Tunneling Diode Photodetector Band diagram Accumulation (LED)Inversion (Detector) The bandgap shrinkage enlarges the concentration of the electron in the bulk silicon, and since the tunneling process would not be the limiting factor for electron to go from p-Si to Al gate, the photo current increases. Namely, the responsivity is enhanced.

NTU GIEE NanoSiOE 11 MOS Tunneling Diode Photodetector Measurement Biaxial tensile strainUniaxial tensile strain The dark current has almost no change under strain, and the photo current is enhanced gradually with increasing strain.

NTU GIEE NanoSiOE 12 MOS Tunneling Diode Photodetector Responsivity enhancement 12% 14% Uniaxial strain has potentiality to achieve higher strain gauge than biaxial strain. The maximum of current enhancement is about 12% and 14% under biaxial and uniaxial strain respectively.

NTU GIEE NanoSiOE 13 Outline  Introduction  Strain-enhanced MOS Photodetector  Strain-enhanced Transimpedance Amplifier  Circuit Design & Simulation  Bandwidth Enhancement by Tensile Strain  7Gb/s Transimpedance Amplifier  SiGe HBT BiCMOS Active Inductor  Summary and Future Work

NTU GIEE NanoSiOE 14 Strain-enhanced Transimpedance Amplifier Circuit schematic Main Gain StagePeaking Stage

NTU GIEE NanoSiOE 15 Strain-enhanced Transimpedance Amplifier Inductive peaking For m = 0.4, the transfer function exhibits a maximum flat response with a bandwidth improvement of 70% compared to a simple common source amplifier. If m = 0.7, the bandwidth reaches its maximum value with 1.5dB peaking and 85% improvement. (τ= RC, m = L/R 2 C ) Active Inductor

NTU GIEE NanoSiOE 16 Strain-enhanced Transimpedance Amplifier Bandwidth enhancement After strain Active Inductor : Peaking Stage :

NTU GIEE NanoSiOE 17 Strain-enhanced Transimpedance Amplifier Frequency response & Stability Magnitude responsePhase response K factorΔ factor Gain: 60dBΩ Bandwidth: 3.5GHz Peaking < 0.5dB K > 1 Δ< 1

NTU GIEE NanoSiOE 18 Strain-enhanced Transimpedance Amplifier Input-referred noise current density & Eye diagram Input-referred noise current density Eye Diagram at 3.125Gb/s, 20uA Jitter < 20ps

NTU GIEE NanoSiOE 19 Strain-enhanced Transimpedance Amplifier TechnologyTSMC 0.18um RFCMOS Supply voltage1.8V Transimpedance gain60dBΩ Bandwidth3.5GHz Input referred noise current < 20pA/√Hz Jitter< 20ps Group delay variation< 65ps Power consumption (core) 12mW Chip Area600*380 um 2 Performance Summary

NTU GIEE NanoSiOE 20 Strain-enhanced Transimpedance Amplifier Measurement : Bandwidth enhancement Through 0.06% biaxial tensile strain, the characteristic of active inductor can be modified, thus improves the -3dB frequency. The bandwidth enhancement is about 5.5%.

NTU GIEE NanoSiOE 21 Strain-enhanced Transimpedance Amplifier Circuit layout & Die photograph Die photo Layout

NTU GIEE NanoSiOE 22 Outline  Introduction  Strain-enhanced MOS Photodetector  Strain-enhanced Transimpedance Amplifier  7Gb/s Transimpedance Amplifier  Circuit Design & Simulation  Measurement  SiGe HBT BiCMOS Active Inductor  Summary and Future Work

NTU GIEE NanoSiOE 23 7Gb/s Transimpedance Amplifier Circuit schematic

NTU GIEE NanoSiOE 24 7Gb/s Transimpedance Amplifier Feedback TIA Frequency response: Noise:

NTU GIEE NanoSiOE 25 7Gb/s Transimpedance Amplifier Frequency response & Stability Magnitude responsePhase response K factorΔ factor Gain: 56dBΩ Bandwidth: 8GHz Peaking < 1dB K > 1 Δ< 1

NTU GIEE NanoSiOE 26 7Gb/s Transimpedance Amplifier Input-referred noise current density & Eye diagram Input-referred noise current density Eye Diagram at 10Gb/s, 20uA Jitter < 15ps

NTU GIEE NanoSiOE 27 7Gb/s Transimpedance Amplifier S11S12 S21S22 Measurement : S-parameters

NTU GIEE NanoSiOE 28 7Gb/s Transimpedance Amplifier Measurement : Frequency response Magnitude responsePhase response Transform function: Gain: 57dBΩ Bandwidth: 6GHz

NTU GIEE NanoSiOE 29 7Gb/s Transimpedance Amplifier Measurement : Eye diagram 2.5 Gb/s PRBS3.125 Gb/s PRBS 7 Gb/s PRBS Measured on PCB. Equivalent input current ~ 50uA. Eye can open well under 7Gb/s PRBS. Jitter < 7Gb/s The inductive characteristic of bond wire may help improve overall bandwidth.

NTU GIEE NanoSiOE 30 7Gb/s Transimpedance Amplifier SimulationMeasurement TechnologyTSMC 0.18um RFCMOS Supply voltage1.8V Transimpedance gain56dBΩ57dBΩ Bandwidth8GHz6GHz Input referred noise current < 15pA/√Hz Sensitivity: 20uA/eye open Jitter< 15ps< 7Gb/s Group delay variation< 80ps< 90ps Power consumption (core) 10mW Chip Area880*980 um 2 Performance Summary

NTU GIEE NanoSiOE 31 7Gb/s Transimpedance Amplifier Die & PCB photograph Die photo PCB photo PCB layout

NTU GIEE NanoSiOE 32 Outline  Introduction  Strain-enhanced MOS Photodetector  Strain-enhanced Transimpedance Amplifier  7Gb/s Transimpedance Amplifier  SiGe HBT BiCMOS Active Inductor  CMOS Active Inductor  BiCMOS Active Inductor  Summary and Future Work

NTU GIEE NanoSiOE 33 SiGe HBT BiCMOS Active Inductor Basic configuration of active inductor Gyrator-C topology: CS-CD type CS-CG type Two-transistor active inductor:

NTU GIEE NanoSiOE 34 SiGe HBT BiCMOS Active Inductor Proposed active inductor CMOS BiCMOS Type AType B Equivalent model : Cascode BiCMOS Type A

NTU GIEE NanoSiOE 35 SiGe HBT BiCMOS Active Inductor Zin analysis Z in

NTU GIEE NanoSiOE 36 SiGe HBT BiCMOS Active Inductor Frequency response of input impedance MagnitudePhase For fair comparison, all the active inductors are designed with identical MOSFET size and power consumption. BiCMOS active inductor has wider inductive range. The phase of BiCMOS type rises at lower frequency and reaches the higher degree, which means BiCMOS type has much higher quality factor and less resistive loss.

NTU GIEE NanoSiOE 37 SiGe HBT BiCMOS Active Inductor Inductance & Quality factor InductanceQ-factor BiCMOS type has much higher resonant frequency. Cascode will reduce the resonant frequency owing to its extra parasitics, but it provides higher inductance at high frequency and higher quality factor.

NTU GIEE NanoSiOE 38 SiGe HBT BiCMOS Active Inductor Inductor characteristic tuning I 1 tuning I 2 tuning V B tuning I 1 increasing I 2 increasing V B increasing InductanceQ-factor

NTU GIEE NanoSiOE 39 Outline  Introduction  Strain-enhanced MOS Photodetector  Strain-enhanced Transimpedance Amplifier  7Gb/s Transimpedance Amplifier  SiGe HBT BiCMOS Active Inductor  Summary and Future Work  Summary  CMOS Image Sensor

NTU GIEE NanoSiOE 40 Summary  A novel metal/thin-oxide/silicon structure tunneling diode photo detector is proposed. With biaxial or uniaxial tensile strain, the band-gap of bulk Si shrinks, resulting in higher electron concentration under identical exposure, thus the responsivity is enhanced. The maximum of responsivity enhancement under biaxial and uniaxial tensile strain are about 12% and 14% respectively.  A Transimpedance Amplifier (TIA) adopting active inductor is designed. Through inductive characteristic tuning by biaxial tensile strain, a 5.5% bandwidth enhancement can be achieved.  A 7Gb/s transimpedance amplifier fabricated with TSMC 0.18um CMOS process is proposed. The measured gain and bandwidth are 57dBΩ and 6GHz respectively. The eye can open well with operation under 7Gb/s PRBS.  A novel BiCMOS type active inductor is proposed. From simulation, it can be proved that BiCMOS active inductor can achieve higher quality factor and resonant frequency than CMOS type with the great help from SiGe HBT. However, the inductance value would be slightly lower.

NTU GIEE NanoSiOE 41 Future Work CMOS image sensor Replace with MOS detector The photodiode can be replaced with our MOS tunneling diode photodetector by connecting the gate of the diode to the source of transfer gate. The lower dark current(~3nA/cm 2 ) and higher quantum efficiency (~80%) can improve the performance of the pixel, such as dynamic range and sensitivity.