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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 26 — Dec. 12, 2011
  • pp: B385–B390
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High-power high-linearity flip-chip bonded modified uni-traveling carrier photodiode

Zhi Li, Yang Fu, Molly Piels, Huapu Pan, Andreas Beling, John E. Bowers, and Joe C. Campbell  »View Author Affiliations


Optics Express, Vol. 19, Issue 26, pp. B385-B390 (2011)
http://dx.doi.org/10.1364/OE.19.00B385


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Abstract

We demonstrate a flip-chip bonded modified uni-traveling carrier (MUTC) photodiode with an RF output power of 0.75 W (28.8 dBm) at 15 GHz and OIP3 as high as 59 dBm. The photodiode has a responsivity of 0.7 A/W, 3-dB bandwidth > 15 GHz, and saturation photocurrent > 180 mA at 11 V reverse bias.

© 2011 OSA

1. Introduction

In this paper, a thermal-reflectance imaging method was used to characterize the surface temperature of conventional backside-illuminated MUTC photodiodes. These measurements enabled calibration of simulation parameters, which were used to generate two-dimensional plots of the temperature distribution inside the photodiode. The thermal modeling predicted that flip-chip bonding to AlN would result in ~70% improvement in the thermal limit. This was verified experimentally. A 40-μm-diameter photodiode achieved 0.7 A/W responsivity (1540 nm), 15 GHz 3-dB bandwidth, and 0.75 W RF output power. The OIP3 at 330 MHz was 59 dBm at 140 mA photocurrent and remained as high as 40 dBm at 15 GHz and 160 mA.

2. Thermal imaging and simulation

To investigate the thermal characteristics of the conventional backside-illuminated photodiode [4

4. Z. Li, H. Pan, H. Chen, A. Beling, and J. C. Campbell, “High-saturation-current modified uni-traveling-carrier photodiode with cliff layer,” IEEE J. Quantum Electron. 46(5), 626–632 (2010). [CrossRef]

], the temperature profile on the surface of the Au contact area was measured by thermo-reflectance imaging [7

7. J. Christofferson, K. Maize, Y. Ezzahri, J. Shabani, X. Wang, and A. Shakouri, “Microscale and nanoscale thermal characterization techniques,” J. Electron. Packag. 130(4), 041101 (2008). [CrossRef]

]. A top-view photograph and a reconstructed thermal image of a 34-µm photodiode are shown in Figs. 1(a)
Fig. 1 (a) The layout image and (b) thermal image of 34-μm backside-illuminated MUTC photodiode.
and 1(b), respectively. The experimental setup measures the change in surface reflectivity using pulses from a green LED array (λ = 530 nm), timed to coincide with the end of the device heating cycle. The reflectivity of the surface is a function of temperature and, thus, the change in reflectivity can be used to obtain the change in temperature. In our measurement, the diode was placed on a thermoelectric cooler maintained at 15°C. A 2-mm-diameter hole in the center of the cooler permitted back-illumination through the InP substrate. The optical input signal was modulated at 400 Hz with 10% duty cycle and the optical illumination was carefully adjusted to ensure a stable outputphotocurrent of 40 mA for each bias level. Adjusting the bias voltage varied the amount of heat generated in the active area. Figure 2(a)
Fig. 2 (a) Measured and simulated surface temperatures of 34- and 40-μm-diameter backside-illuminated photodiodes under different heat generation levels. (b) Simulated surface temperature distribution of 40-μm-diameter photodiode with 680 mW heat flow.
shows the measured surface temperature of 34- and 40-μm-diameter backside-illuminated photodiodes versus power dissipation. The imaging measurements were carried out with increasing power dissipation until the devices failed; catastrophic failure occurred when the surface temperature was ~500 K. The relatively low surface temperature at failure can be attributed to lateral inhomogeneities, which create “hot spots”, as shown in Fig. 1(b). A simulation model was created using the finite element analysis tool ANSYS. The model structure follows the epitaxial structure layout of MUTC2 in [4

4. Z. Li, H. Pan, H. Chen, A. Beling, and J. C. Campbell, “High-saturation-current modified uni-traveling-carrier photodiode with cliff layer,” IEEE J. Quantum Electron. 46(5), 626–632 (2010). [CrossRef]

]. The backside of the diode was set at 15°C and the environment temperature was set at 23°C to simulate the same environmental conditions as the measurement. As shown in Fig. 2(a) good agreement with the measurements was achieved. The parameters obtained from thermal imaging were incorporated into the two-dimensional model.

It was found that catastrophic thermal failure occurs when the core temperature of a 40-μm photodiode is ~470 K with dissipated power of 680 mW as shown in Fig. 3(a)
Fig. 3 Simulated vertical cross section temperature distribution of a 40-μm MUTC photodiode: (a) conventional back-illuminated structure, (b) flip-chip bonded on AlN substrate with 680 mW power dissipation.
. For flip-chip bonding to an AlN substrate through 8-μm thick gold vias the core temperature was reduced to 370 K for the same operating conditions, Fig. 3(b). In order to reach the same failure core temperature of 470 K, the dissipated power of the flip-chip device can increase to 1.15 W, which means the flip-chip bonded photodiode shows a thermal limit enhancement of 70%.

3. Photodiode structure

The epitaxial layer structure of the active diode structure was grown by MOCVD on semi-insulating InP substrate. The detailed diode structure can be found in [4

4. Z. Li, H. Pan, H. Chen, A. Beling, and J. C. Campbell, “High-saturation-current modified uni-traveling-carrier photodiode with cliff layer,” IEEE J. Quantum Electron. 46(5), 626–632 (2010). [CrossRef]

] labeled as MUTC2. The diameter of the diode is 40 µm and the total depletion thickness is 1.18 µm. The wafer was fabricated into back-illuminated double-mesa structures via ICP etching. A 250 nm-thick SiO2 film was deposited on the backside as anti-reflection coating. Gold contact vias were up-plated on p- and n- mesas to serve as electrical contacts and heat dissipation paths. The wafer was cut into 2.8 mm × 1.2 mm chips and flip-chip bonded onto a gold contact pad circuit on 0.5-mm thick AlN. The finished flip-chip photodiode cross section and SEM picture are shown in Figs. 4(a)
Fig. 4 (a) Cross-sectional schematic view of the photodiode. (b) SEM picture of the bonded chip on probe pads.
and 4(b), respectively.

4. Measurement results

The frequency tunable optical input was obtained from two equal power heterodyned DFB lasers operating near 1540 nm. The modulation depth was 100% and the frequency was swept by tuning the temperature of one of the lasers. The measured responsivity was 0.7 A/W at 1-mA photocurrent and 5-V reverse bias. Figure 5(a)
Fig. 5 (a) Frequency responses of 40-μm flip-chip bonded photodiode under various photocurrent conditions at 5-V reverse bias. (b) S-parameter S11 of 40-μm flip-chip MUTC2 photodiode at various bias levels.
shows the frequency responses of a 40-µm-diameter flip-chip bonded photodiode under 5 V reverse bias and various photocurrent levels. The 3-dB bandwidth was >15 GHz when the photocurrent was greater than 40 mA. The bandwidth increased with increasing photocurrent, which can be attributed to carrier acceleration by the enhanced self-induced field in the gradated p-type absorber [8

8. H. Ito, S. Kodama, Y. Muramoto, T. Furuta, T. Nagatsuma, and T. Ishibashi, “High-speed and high-output InP-InGaAs unitraveling-carrier photodiodes,” IEEE J. Sel. Top. Quantum Electron. 10(4), 709–727 (2004). [CrossRef]

]. The S-parameter S11 of the 40-μm flip-chip bonded photodiode at various bias levels is plotted in Fig. 5(b). The extracted capacitance of 210 fF at 5-V reverse bias is 50 fF higher than a backside-illuminated photodiode of the same diameter. The extra capacitance is due to the relatively large pad surface area in the bonding region that was employed for alignment tolerance. The series resistance from S11 measurement is only 2 Ω.

Figure 6(a)
Fig. 6 (a) Measured RF power versus average photocurrent at 15 GHz, under various bias levels. (b) Maximum output power at various bias levels versus frequency.
shows the measured output RF power versus average photocurrent at 15 GHz under various reverse bias conditions. The space-charge-limited saturation effect has been greatly mitigated through the cliff layer structure [4

4. Z. Li, H. Pan, H. Chen, A. Beling, and J. C. Campbell, “High-saturation-current modified uni-traveling-carrier photodiode with cliff layer,” IEEE J. Quantum Electron. 46(5), 626–632 (2010). [CrossRef]

], and with improved thermal dissipation, the 40-μm diameter photodiode was able to operate under a high reverse bias of 11 V and 180 mA photocurrent without saturation. The RF power from a single photodiode at 15 GHz was 0.75 W (28.8 dBm). Figure 6(b) shows the maximum output power versus frequency for different operating conditions, 5V/130mA to 11V/180mA.

We define the dissipated power in the photodiode as the product (V*Iavg), where V is the applied reverse bias voltage and Iavg is the average photocurrent. With V = 11 V and Iavg = 180 mA it follows that the power dissipated by the photodiode is 1.98 W. Recall that the maximum power dissipated by the backside-illuminated photodiode of equal size was only 0.91 W [4

4. Z. Li, H. Pan, H. Chen, A. Beling, and J. C. Campbell, “High-saturation-current modified uni-traveling-carrier photodiode with cliff layer,” IEEE J. Quantum Electron. 46(5), 626–632 (2010). [CrossRef]

].

5. Conclusions

A MUTC photodiode flip-chip bonded on AlN substrate has been demonstrated. Thermal imaging and simulation were utilized to characterize thermal failure and implement improved heat dissipation. The responsivity was 0.7 A/W and the 3-dB bandwidth was 15 GHz. Saturation current > 180 mA was measured for reverse bias greater than 9 V leading to an output power of 0.75 W at 15 GHz. At 330 MHz, a high OIP3 > 59 dBm was obtained at 140 mA, while the OIP3 at 15 GHz was 40 dBm at a photocurrent of 160 mA.

Acknowledgments

References and links

1.

K. J. Williams, L. T. Nichols, and R. D. Esman, “Photodetector nonlinearity limitations on a high-dynamic range 3 GHz fiber optic link,” J. Lightwave Technol. 16(2), 192–199 (1998). [CrossRef]

2.

P.-L. Liu, K. J. Williams, M. Y. Frankel, and R. D. Esman, “Saturation characteristics of fast photodetectors,” IEEE Trans. Microw. Theory Tech. 47(7), 1297–1303 (1999). [CrossRef]

3.

T. Ishibashi and N. Shimizu, “Uni-traveling-carrier photodiodes,” in Ultrafast Electron. Optoelectron. ’97 Conf., Incline Village, NV (1997).

4.

Z. Li, H. Pan, H. Chen, A. Beling, and J. C. Campbell, “High-saturation-current modified uni-traveling-carrier photodiode with cliff layer,” IEEE J. Quantum Electron. 46(5), 626–632 (2010). [CrossRef]

5.

F.-M. Kuo, M.-Z. Chou, and J.-W. Shi, “Linear-cascaded near-ballistic unitraveling-carrier photodiodes with an extremely high saturation current-bandwidth product,” J. Lightwave Technol. 29(4), 432–438 (2011). [CrossRef]

6.

S. Itakura, K. Sakai, T. Nagatsuka, E. Ishimura, M. Nakaji, H. Otsuka, K. Mori, and Y. Hirano, “High-current backside-illuminated photodiode array module for optical analog links,” J. Lightwave Technol. 28(6), 965–971 (2010). [CrossRef]

7.

J. Christofferson, K. Maize, Y. Ezzahri, J. Shabani, X. Wang, and A. Shakouri, “Microscale and nanoscale thermal characterization techniques,” J. Electron. Packag. 130(4), 041101 (2008). [CrossRef]

8.

H. Ito, S. Kodama, Y. Muramoto, T. Furuta, T. Nagatsuma, and T. Ishibashi, “High-speed and high-output InP-InGaAs unitraveling-carrier photodiodes,” IEEE J. Sel. Top. Quantum Electron. 10(4), 709–727 (2004). [CrossRef]

9.

H. Pan, Z. Li, A. Beling, and J. C. Campbell, “Characterization of high-linearity modified uni-traveling carrier photodiodes using three-tone and bias modulation techniques,” J. Lightwave Technol. 28(9), 1316–1322 (2010). [CrossRef]

10.

A. Beling, H. Pan, H. Chen, J. C. Campbell, A. Hastings, D. A. Tulchinsky, and K. J. Williams, “Impact of voltage-dependent responsivity on photodiode non-linearity,” in Proc. LEOS 2008, Newport Beach, CA, Nov. 2008, pp. 157–158.

11.

Y. Fu, H. Pan, Z. Li, A. Beling, and J. C. Campbell, “Characterizing and modeling nonlinear intermodulation distortions in modified uni-travelling carrier photodiodes,” IEEE J. Quantum Electron. 47(10), 1312–1319 (2011). [CrossRef]

12.

H. Pan, A. Beling, H. Chen, J. C. Campbell, and P. D. Yoder, “The influence of nonlinear capacitance on the linearity of a modified unitraveling carrier photodiode,” in Proc. MWP 2008, Gold Coast, Australia, Oct. 2008, pp. 82–85.

13.

D. A. Tulchinsky, J. B. Boos, D. Park, P. G. Goetz, W. S. Rabinovich, and K. J. Williams, “High-current photodetectors as efficient, linear, and high-power RF output stages,” J. Lightwave Technol. 26(4), 408–416 (2008). [CrossRef]

14.

T. Ohno, H. Fukano, Y. Muramoto, T. Ishibashi, T. Yoshimatsu, and Y. Doi, “Measurement of intermodulation distortion in a uni-traveling carrier refracting-facet photodiode and a p-i-n refracting-facet photodiode,” IEEE Photon. Technol. Lett. 14(3), 375–377 (2002). [CrossRef]

15.

M. Chtioui, A. Enard, D. Carpentier, S. Bernard, B. Rousseau, F. Lelarge, F. Pommereau, and M. Achouche, “High-power high-linearity uni-traveling-carrier photodiodes for analog photonic links,” IEEE Photon. Technol. Lett. 20(3), 202–204 (2008). [CrossRef]

OCIS Codes
(040.5160) Detectors : Photodetectors
(230.5170) Optical devices : Photodiodes

ToC Category:
Waveguide and Opto-Electronic Devices

History
Original Manuscript: October 3, 2011
Revised Manuscript: October 30, 2011
Manuscript Accepted: November 1, 2011
Published: November 18, 2011

Virtual Issues
European Conference on Optical Communication 2011 (2011) Optics Express

Citation
Zhi Li, Yang Fu, Molly Piels, Huapu Pan, Andreas Beling, John E. Bowers, and Joe C. Campbell, "High-power high-linearity flip-chip bonded modified uni-traveling carrier photodiode," Opt. Express 19, B385-B390 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-26-B385


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References

  1. K. J. Williams, L. T. Nichols, and R. D. Esman, “Photodetector nonlinearity limitations on a high-dynamic range 3 GHz fiber optic link,” J. Lightwave Technol.16(2), 192–199 (1998). [CrossRef]
  2. P.-L. Liu, K. J. Williams, M. Y. Frankel, and R. D. Esman, “Saturation characteristics of fast photodetectors,” IEEE Trans. Microw. Theory Tech.47(7), 1297–1303 (1999). [CrossRef]
  3. T. Ishibashi and N. Shimizu, “Uni-traveling-carrier photodiodes,” in Ultrafast Electron. Optoelectron. ’97 Conf., Incline Village, NV (1997).
  4. Z. Li, H. Pan, H. Chen, A. Beling, and J. C. Campbell, “High-saturation-current modified uni-traveling-carrier photodiode with cliff layer,” IEEE J. Quantum Electron.46(5), 626–632 (2010). [CrossRef]
  5. F.-M. Kuo, M.-Z. Chou, and J.-W. Shi, “Linear-cascaded near-ballistic unitraveling-carrier photodiodes with an extremely high saturation current-bandwidth product,” J. Lightwave Technol.29(4), 432–438 (2011). [CrossRef]
  6. S. Itakura, K. Sakai, T. Nagatsuka, E. Ishimura, M. Nakaji, H. Otsuka, K. Mori, and Y. Hirano, “High-current backside-illuminated photodiode array module for optical analog links,” J. Lightwave Technol.28(6), 965–971 (2010). [CrossRef]
  7. J. Christofferson, K. Maize, Y. Ezzahri, J. Shabani, X. Wang, and A. Shakouri, “Microscale and nanoscale thermal characterization techniques,” J. Electron. Packag.130(4), 041101 (2008). [CrossRef]
  8. H. Ito, S. Kodama, Y. Muramoto, T. Furuta, T. Nagatsuma, and T. Ishibashi, “High-speed and high-output InP-InGaAs unitraveling-carrier photodiodes,” IEEE J. Sel. Top. Quantum Electron.10(4), 709–727 (2004). [CrossRef]
  9. H. Pan, Z. Li, A. Beling, and J. C. Campbell, “Characterization of high-linearity modified uni-traveling carrier photodiodes using three-tone and bias modulation techniques,” J. Lightwave Technol.28(9), 1316–1322 (2010). [CrossRef]
  10. A. Beling, H. Pan, H. Chen, J. C. Campbell, A. Hastings, D. A. Tulchinsky, and K. J. Williams, “Impact of voltage-dependent responsivity on photodiode non-linearity,” in Proc. LEOS 2008, Newport Beach, CA, Nov. 2008, pp. 157–158.
  11. Y. Fu, H. Pan, Z. Li, A. Beling, and J. C. Campbell, “Characterizing and modeling nonlinear intermodulation distortions in modified uni-travelling carrier photodiodes,” IEEE J. Quantum Electron.47(10), 1312–1319 (2011). [CrossRef]
  12. H. Pan, A. Beling, H. Chen, J. C. Campbell, and P. D. Yoder, “The influence of nonlinear capacitance on the linearity of a modified unitraveling carrier photodiode,” in Proc. MWP 2008, Gold Coast, Australia, Oct. 2008, pp. 82–85.
  13. D. A. Tulchinsky, J. B. Boos, D. Park, P. G. Goetz, W. S. Rabinovich, and K. J. Williams, “High-current photodetectors as efficient, linear, and high-power RF output stages,” J. Lightwave Technol.26(4), 408–416 (2008). [CrossRef]
  14. T. Ohno, H. Fukano, Y. Muramoto, T. Ishibashi, T. Yoshimatsu, and Y. Doi, “Measurement of intermodulation distortion in a uni-traveling carrier refracting-facet photodiode and a p-i-n refracting-facet photodiode,” IEEE Photon. Technol. Lett.14(3), 375–377 (2002). [CrossRef]
  15. M. Chtioui, A. Enard, D. Carpentier, S. Bernard, B. Rousseau, F. Lelarge, F. Pommereau, and M. Achouche, “High-power high-linearity uni-traveling-carrier photodiodes for analog photonic links,” IEEE Photon. Technol. Lett.20(3), 202–204 (2008). [CrossRef]

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