SiC Diode Lateral Conduction Reduces On-Resistance
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Solution Overview
Problem
Silicon carbide diodes exhibit higher series resistance due to the substrate's high resistivity, which is not effectively reduced by existing methods, hindering their performance in RF applications where low RF on-resistance is crucial.
Innovation Solution
The method involves forming a laterally conductive PIN diode with a top contact and a cathode on the same side of a highly doped n+ layer, utilizing a nonconductive mesa sidewall spacer and metal silicide contacts to minimize series resistance by enabling lateral current conduction across the n+ layer, rather than through the substrate thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the SiC substrate is thinned to reduce substrate series resistance, then the on-resistance decreases, but the manufacturing complexity and yield loss increase
Solution Approach 1:
The patent transitions from vertical current flow (through the substrate thickness) to lateral current flow (across the substrate surface). By forming contacts on the same side of the substrate and utilizing lateral conduction through the highly doped n+ layer, the current path is redirected from the thickness dimension to the surface dimension, achieving low resistance without substrate thinning
Solution Approach 2:
The patent divides the current conduction path into multiple parallel lateral paths across the highly doped n+ layer. By creating an extended lateral conduction region with multiple contact points, the total resistance is reduced through parallel conduction paths, eliminating the need to reduce substrate thickness
2Loss of energy
If the SiC substrate is thinned to reduce on-resistance, then the series resistance decreases, but the yield loss increases
Solution Approach 1:
The invention changes the current conduction from vertical (through substrate thickness) to lateral (across substrate surface), eliminating the need for substrate thinning and associated yield losses from complex thinning processes and handling of fragile thin substrates
Solution Approach 2:
The highly doped n+ layer is formed in advance with sufficient lateral extent to provide low resistance conduction paths. This preliminary preparation of the doped layer ensures low series resistance before any subsequent processing, avoiding yield loss from post-growth substrate manipulation
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
This approach significantly reduces forward resistance in silicon carbide diodes, allowing for improved performance in high-voltage blocking and RF applications with substrates as thin as 50 microns, while maintaining high voltage blocking capabilities.
Implementation Method 1
utilizing a nonconductive mesa sidewall spacer and metal silicide contacts to minimize series resistance by enabling lateral current conduction across the n+ layer
Implementation Method 2
metal silicide contacts to minimize series resistance
Data Source
Figure 1~2
Figure 3
AI summary
A diode structure (20) having a reduced on-resistance in the forward-biased condition includes semiconductor layers, preferably of silicon carbide. The anode (21) and cathode (30) of the device are located on the same side of the bottom semiconductor layer (35), providing lateral conduction across the diode body. The anode is positioned on a semiconductor mesa (22), and the sides of the mesa are covered with a nonconductive spacer (24) extending from the anode to the bottom layer. An ohmic contact (33), preferably a metal silicide, covers the surface of the bottom layer between the spacer material and the cathode. The conductive path extends from anode to cathode through the body of the mesa and across the bottom semiconductor layer, including the ohmic contact. The method of forming the diode includes reacting layers of silicon and metal on the appropriate regions of the diode to form an ohmic contact of metal silicide.