Flip-Chip Bonding Packaged THz Photodiode With Broadband High-Power Performance

Design and analysis of the flip-chip bonding package for near-ballistic unitraveling-carrier photodiodes (NBUTC-PDs) with reliable high-power performance from dc to sub-THz (~300 GHz) frequency has been demonstrated. According to our simulation and measurement results, the geometric size of flipchip bonding structure becomes a major limitation in speed and output power when the operating frequency is over ~100 GHz. In order to overcome this problem, the position of Au/Sn bump on bottom AlN substrate for bonding process, must be as close as possible with the active PD mesa on the InP substrate at topside. Compared with the control with a longer spacing (~90 versus 25 μm), our device not only exhibits a broader bandwidth (225 versus 200 GHz), but also a higher saturation current (13 versus 9 mA). With such an optimized flip-chip bonding structure for package of NBUTC-PD, a wide 3-dB bandwidth (~225 GHz), high saturation current (13 mA), and a 0.67-mW maximum output power at 260-GHz operating frequency have been achieved simultaneously.