Optical Interconnection Between Flip-chip Bonded Photodiodes And Optical Polyimide Waveguides On An Opto-electronic Multichip Module

An opto-electronic multichip module (OE-MCM) has been developed for high speed and wide-band communication systems(1). In this work, the opto-electronic performance for the interconnection between flip-chip bonded photodiodes (PDs) and fluorinated polyimide waveguides on the OE-substrtate is studied. A 3.5 GHzbandwidth response of the interconnection was achieved by using total internal reflection (TIR) mirrors. Low loss (0.4 dB/cm at a 1.3,U m wavelength) polyimide waveguides (50 f l m wide and 87.5 p m high) were fabricated on a copper-polyimide multilayer substrate by using a conventional MCM process and reactive ion etching(2) (3). The waveguide-to-PD interconnection is attained by using a TIR mirror fabricated at the edge of the waveguides, while tilting the OE-substrate to the normal direction of the cathode. The mirror angle was easily determined to be 44.5" from the radiated reflection-beam angle by using the far-field pattern method. The reflection loss of the mirror is less than 1.5 dB at a 1.3-,U m wavelength. An InP PD was easily flip-chip bonded with conventional Sn/Pb (60/40) solder balls positioned in the solder ball guides. The propagated light in the waveguide is totally reflected by the mirror. The bandwidth was measured while propagating the light using a heterodyne optical sweeper (1.55-,U m wavelength). The output of the PD was connected directly to a component analyzer. The frequency response of the PD with a sensitive diameter of 80 p m is shown in Fig. 4. bandwidth was determined to be 3.5 GHz, being limited by the PD response. This optical interconnection will therefore be useful in developing high speed and wide-band OE-MCMs. A schematic representation of the OE-MCM is shown in Fig. 1.