A Bias-Dependent Equivalent-Circuit Model of Evanescently Coupled Photodiode (ECPD) Advisers : J.- W. Shi, Y.- J. Chan Student : Y.- S. Wu

National Central University Micro-Optoelectronic Labs Taiwan

IV. Model Extraction I. Motivation III. Measurement System II. The Structure of ECPD V. The Fitting Results VI. Conclusions Outline

IV. Model Extraction I. Motivation III. Measurement System II. The Structure of ECPD V. The Fitting Results VI. Conclusions

+ Transmitter for Fiber-Radio Communication System + mm-Wave Detector PhotodiodeMatching CircuitAntenna Transmitter Module The loss of electrical signal can be reduced through wireless communication system. To simplify the base station by eliminating the costly post amplifiers and cables.

+ Transmitter for Fiber-Radio Communication System + Mm-Wave Detector PhotodiodeMatching CircuitAntenna Transmitter Module The loss of electrical signal can be reduced through wireless communication system. To simplify the base station by eliminating the costly post amplifiers and cables. The model extraction of PD serves as a key approach to design the transmitter module

IV. Model Extraction I. Motivation III. Measurement System II. The Structure of ECPD V. The Fitting Results VI. Conclusions

Epi-Layer structure ECPD Geometric structure ECPD: Three major target can be achieved simultaneously Epi-layer structure: Partially p-doped photo-absorption layer Geometric structure: Evanescently coupled waveguide The ECPD We Used in Our Model Extraction!!

Electrical Bandwidth (with Different Reverse Bias ) The measured frequency responses of device A under three different dc bias voltages.

RF power versus dc photocurrent of ECPD for different reverse at 40GHz. High Power Performance

IV. Model Extraction I. Motivation III. Measurement System II. The Structure of ECPD V. The Fitting Results VI. Conclusions

Heterodyne-Beating Measurement Setup (Large Signal Measurement) Bias Tee Mechanical Pump (fasten the sample ) Power supply & current meter Polarization controller EDFA (for high power generation ) Coupler Polarization controller Tunable laser OM Power meter Spectrum (for high frequency 40GHz) Holder Piezoelectrical stage sample Fiber electric cord (DC) electric cord (AC) - By increasing the wavelength difference, the bandwidth response is available through recording the amplitude of RF tone signal. Can measure the BW response and power generation

LNA Measurement Setup (Small Signal Measurement) Port 1 Port 2 EDFA Power supply Tunable Laser Polarization Controller 1.Calibrate the packaged Modulator and save as s2p file 2.Don’t change the bias voltage & polarization of the Modulator 3.De-embedded the Modulator Lightning Network Analyzers Step 1 Step 2 Modulator Not only measure amplitude response but also phase response Anritsu 37300C VNA + MN4765A (commercial PD)

IV. Model Extraction I. Motivation III. Measurement System II. The Structure of ECPD V. The Fitting Results VI. Conclusions

Rs Z=50 Ω Cp Csc Rt Ct CdxCj L RC delay time region (f RC ) Space charge screen effect region (f sc ) The Equivalent Circuit Model Transit time region (f t ) G=0.013 S Z=50 Ω The frequency response can be determined by three major factors Gang Wang, and Tsuneo Tokumitsu, IEEE Trans. Microwave Theory Tech., 15 (2003) 1227.

Rs Z=50 Ω Cp Csc Rt Ct CdxCj L The Equivalent Circuit Model G=0.013 S Z=50 Ω S 22 The components in right hand of the equivalent circuit can be verified by fitting the S22 parameter. Electrical signal

Rs Z=50 Ω Cp Csc Rt Ct CdxCj L The Equivalent Circuit Model G=0.013 S Z=50 Ω S 22 S 21 All the components in the equivalent circuit can be verified by fitting the S21 parameter. Space charge screen effect region (f sc ) Transit time region (f t ) Optical signalElectrical signal

Rc Contact Resistance Rj Junction Resistance Cj Junction Capacitance Cdx BCB Capacitance Cp Pad Capacitance Lg Inductance of Contact Metal Ls Inductance of Pad The Definition of Parameters in This Equivalent Circuit

The Step of Model Extraction!! Part 1 : Determine right hand of equivalent circuit Measure the S 22 parameters of ECPD Frequency (50MHz to 40GHz) Measured S22

The Step of Model Extraction!! Part 1 : Determine right hand of equivalent circuit Measure the S 22 parameters of ECPD Measure the S 22 parameters of coplanar electrical pad

The Step of Model Extraction!! Part 1 : Determine right hand of equivalent circuit Measure the S 22 parameters of ECPD Measure the S 22 parameters of coplanar electrical pad (L, Cdx, Cp) Cdx Cp L

The Step of Model Extraction!! Part 1 : Determine right hand of equivalent circuit Measure the S 22 parameters of ECPD Measure the S 22 parameters of coplanar electrical pad (L, Cdx, Cp) Perform the I-V measurement

The Step of Model Extraction!! Part 1 : Determine right hand of equivalent circuit Measure the S 22 parameters of ECPD Measure the S 22 parameters of coplanar electrical pad (L, Cdx, Cp) Perform the I-V measurement (Rs) Rs

The Step of Model Extraction!! Part 1 : Determine right hand of equivalent circuit Measure the S 22 parameters of ECPD Measure the S 22 parameters of coplanar electrical pad (L, Cdx, Cp) Perform the I-V measurement (Rs) Perform the C-V measurement (total capacitance)

The Step of Model Extraction!! Part 1 : Determine right hand of equivalent circuit Measure the S 22 parameters of ECPD Measure the S 22 parameters of coplanar electrical pad (L, Cdx, Cp) Perform the I-V measurement (Rs) Perform the C-V measurement (total capacitance) Cj

The Step of Model Extraction!! Part 2 : Determine left hand of equivalent circuit Measure the S 21 parameters of ECPD under different photocurrent and bias voltage

The Step of Model Extraction!! Part 2 : Determine left hand of equivalent circuit Measure the S 21 parameters of ECPD under different photocurrent and bias voltage Fit the S 21 parameters under high bias voltage and low photocurrent (Rt, Ct) Rt Ct

The Step of Model Extraction!! Part 2 : Determine left hand of equivalent circuit Measure the S 21 parameters of ECPD under different photocurrent and bias voltage Fit the S 21 parameters under high bias voltage and low photocurrent (Rt, Ct) Fit the S 21 parameters under low bias voltage and high photocurrent (Csc) Csc

IV. Model Extraction I. Motivation III. Measurement System II. The Structure of ECPD V. The Fitting Results VI. Conclusions

The Fitting Result of S22 Parameter The demonstrated model can fit well with the measurement result that obtained under -3V bias voltage with 150 μm 2 active area.

The Fitting Result of S21 Parameter The space charge screen effect will reduce as the bias voltage increases !!

The Fitting Result of S21 Parameter The space charge screen effect is very obvious under low bias voltage and high current generation.

The Bias & Photocurrent-Dependent Csc Parameter The device speed performance won’t degrade under high bias voltage as the photocurrent increases due to the elimination of space-charge capacitance.

IV. Model Extraction I. Motivation III. Measurement System II. The Structure of ECPD V. The Fitting Results VI. Conclusions

Conclusions By concerning the relationship between the influence of bias voltage and photocurrent in the equivalent circuit-model of high power PD, such model is more convenient for systems and circuits integration especially under high RF power applications.

J. W. Shi and Y. S. Wu, IEEE Photon. Technol. Lett., 17 (2005) High-Speed, High-Responsivity, and High-Power Performance of Near-Ballistic Uni-Traveling-Carrier Photodiode at 1.55  m Wavelength The Model Extraction of BUTC Under High Photocurrent