Optimized Wire Bonding for Integrated Modulator Laser Diode
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Solution Overview
Problem
Optical transmission modules for high-speed optical fiber transfer at 10 Gbit/s face challenges in reducing small signal reflection coefficient (S11) and suppressing peaking in small signal passage characteristics (S21) while operating on a single power source, leading to increased component count and size due to the need for separate negative power sourcing and DC-DC converters.
Innovation Solution
An optical transmission module design featuring an optical modulator integrated laser element with a cathode electrode on the board surface, a ground electrode, and a terminal resistor, where the anode and cathode electrodes are connected to the ground via bonding wires, optimizing the placement of bonding wires to minimize inductance and mutual inductance, thereby reducing S11 and S21 issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If the optical modulator integrated laser diode of the related art that is driven by the positive and negative two power sources is used for the transmission portion of the transceiver, then the device can operate with proper power sourcing, but the negative power source must be separately secured inside the transceiver and a DC-DC converter must be mounted, causing the number of components to increase and the mounting area to increase
Solution Approach 1:
The patent merges the negative power source function into the optical modulator integrated laser diode chip itself by providing a ground electrode on the chip surface that can be directly connected to the negative power source terminal. This eliminates the need for separate DC-DC converters and reduces the number of components to be mounted on the transceiver.
Solution Approach 2:
The patent changes the electrode configuration from a conventional side-contact structure to a surface-contact structure where the ground electrode is disposed on the chip surface. This dimensional change allows direct connection to the negative power source without requiring additional mounting components, thereby reducing device complexity.
2Reliability
If one of the ends of the terminal resistor is connected to the ground electrode through a ground via-hole as in the related art, then the circuit can be completed, but the cathode or anode terminal of the optical modulator element disposed on the chip surface must be connected to the ground electrode by the bonding wire, creating unnecessary gain peaking in small signal passage characteristics
Solution Approach 1:
The patent extracts the ground connection function from the terminal resistor and assigns it to a dedicated ground electrode on the chip surface. This separation allows the terminal resistor to be connected directly to the modulator electrode without introducing harmful inductance, while the ground electrode provides the necessary ground connection path.
Solution Approach 2:
The ground electrode acts as an intermediary element between the terminal resistor and the negative power source. By providing a low-inductance ground connection path through this intermediate structure, the patent eliminates the harmful effects of bonding wire inductance while maintaining proper circuit connectivity.
3Object-generated harmful factors
If the bonding wire length is shortened to reduce inductance, then the peaking in small signal passage characteristics may be reduced, but the packaging constraints limit how short the bonding wire can be made
Solution Approach 1:
The patent transitions from a side-contact electrode configuration to a surface-contact electrode configuration. This dimensional change allows the ground electrode to be disposed on the chip surface, enabling direct connection to the negative power source terminal without requiring long bonding wires, thus reducing inductance while satisfying packaging constraints.
Solution Approach 2:
The ground electrode on the chip surface serves the dual function of providing ground connection and enabling direct negative power source connection. This self-service structure eliminates the need for separate ground via-holes and reduces the number of bonding wires required, thereby reducing inductance without complicating the manufacturing process.
Data Source
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Figure 3~4
AI summary
The optical transmission module of the invention uses a semiconductor chip (122) forming an optical modulator integrated laser on a semi-insulating semiconductor board (223). A first input transfer line (227) and a cathode electrode of an optical modulator element (121) are connected by a first bonding wire (131). The cathode electrode of the optical modulator element (121) and one of the ends of a terminal resistor element (24) are connected by a second bonding wire (132). The anode electrode of the optical modulator element (121) and the other end of the terminal resistor element (24) are connected by a third bonding wire (133). The anode electrode of the optical modulator element (121) and a pattern electrode of a second input transfer line (226) are connected by a fourth bonding wire (134).