Fast Recovery Inverse Diode Bulk Silicon Ion Implantation
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Solution Overview
Problem
Conventional inverse diodes with epitaxial silicon structures exhibit degradation in reverse breakdown voltage stability over time, particularly when subjected to high reverse voltages and commutation applications, due to interface quality issues and potential damage from high energy electron irradiation.
Innovation Solution
The development of a fast recovery inverse diode structure without epitaxial silicon, featuring a bottomside P-type anode region and N-type drift region, with a deep layer of hydrogen ions and a shallow layer of hydrogen or helium ions, which reduces charge carrier lifetime and injection efficiency, and forms a P-type isolation structure using bulk silicon, avoiding ion implantation through the silicon/passivation interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If epitaxial silicon structures are used in inverse diodes, then the diode can achieve high reverse breakdown voltage capabilities, but the reverse breakdown voltage stability degrades over time due to interface quality issues and damage from high energy electron irradiation
Solution Approach 1:
The patent removes the epitaxial silicon layer entirely, extracting the problematic interface between epitaxial silicon and bulk silicon. The diode structure uses only bulk silicon wafer material for both the P-type anode region and N-type drift region, eliminating the interface quality issues and susceptibility to high energy electron irradiation damage that cause long term degradation in conventional epitaxial-based inverse diodes
Solution Approach 2:
The patent inverts the conventional diode structure by placing the P-type region at the bottom instead of the top. This inverse configuration, combined with the elimination of epitaxial silicon, creates a structure where the P-type anode region is formed directly in the bulk silicon substrate, fundamentally changing how the device handles high reverse voltage stress and improving long term reliability
2Loss of time
If the reverse recovery time is reduced for fast diode operation, then the diode can operate at higher frequencies, but the structural complexity and manufacturing challenges increase
Solution Approach 1:
The patent achieves fast reverse recovery time by precisely controlling the doping parameters of the bulk silicon regions. The P-type anode region uses a doping concentration of 1×10^16 to 1×10^18 atoms/cm³, while the N-type drift region uses 1×10^15 to 1×10^17 atoms/cm³. By optimizing these doping parameters and the thickness of the N-type drift region, the patent achieves approximately 200 nanosecond reverse recovery time without introducing complex device structures
Solution Approach 2:
The patent creates localized regions with different electrical properties within the bulk silicon. The P-type anode region has specific doping characteristics, the N-type drift region has different doping characteristics, and the space charge region has unique properties due to the doping profile. This local differentiation of material properties enables fast recovery while maintaining structural simplicity
3Reliability
If a lightly doped P-type anode region is used, then the reverse breakdown voltage increases, but the charge carrier injection efficiency increases which may slow down recovery
Solution Approach 1:
The patent optimizes the doping concentration parameter of the P-type anode region to a specific range of 1×10^16 to 1×10^18 atoms/cm³, which is lighter than conventional inverse diodes to achieve high reverse breakdown voltage (100V to 10kV). Simultaneously, the patent controls the thickness and doping of the N-type drift region to balance carrier injection and extraction, achieving fast recovery despite the lightly doped anode
Solution Approach 2:
The patent pre-configures the doping profiles and layer thicknesses during manufacturing to anticipate and manage the trade-off between breakdown voltage and recovery speed. The N-type drift region is pre-formed with specific characteristics that facilitate rapid carrier extraction, compensating for the higher injection efficiency resulting from the lightly doped P-type anode region
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The structure maintains high reverse breakdown voltage stability and achieves a fast reverse recovery time of approximately 200 nanoseconds, even under prolonged high reverse voltage conditions, without degrading the diode's ruggedness, and is suitable for high-frequency switching applications.
Implementation Method 1
a deep layer of hydrogen ions is formed in the N- type drift region
Implementation Method 2
a shallow layer of hydrogen or helium ions is formed
Implementation Method 3
the principal P-N junction of the inverse diode is the junction between the top of the bottomside P-type silicon region and the bottom of the N- type silicon region
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
An inverse diode die has a high reverse breakdown voltage, a short reverse recovery time Trr, and is rugged in terms of reverse breakdown voltage stability over long term use in hard commutation applications. The die has an unusually lightly doped bottomside P type anode region and also has an N- type drift region above it. Both regions are of bulk wafer material. An N+ type contact region extends down into the drift region. A topside metal electrode is on the contact region. A P type silicon peripheral sidewall region laterally rings around the drift region. A topside passivation layer rings around the topside electrode. A bottomside metal electrode is on the bottom of the die. The die has a deep layer of hydrogen ions that extends through the N- drift region. The die also has a shallow layer of ions. Both ion layers are implanted from the bottomside.