Polysilicon Protective Diode for Electric Field Control
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Solution Overview
Problem
The protective diodes in existing semiconductor devices suffer from increased leakage current and breakdown voltage failure due to localized deterioration of the pn junction when frequently subjected to clamping voltage, leading to a larger area and increased electric field concentration.
Innovation Solution
A semiconductor device with a protective diode structure featuring a polysilicon layer with a specific unit structure, including layers of varying impurity concentrations and high-resistance layers, is implemented to clamp surge voltages and reduce electric field concentration on the pn junction, connected between the collector and gate of an insulated gate switching element.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protective diode with a simple pn junction structure is used, then the device area is small and manufacturing is simple, but the leakage current increases and breakdown voltage reliability deteriorates when frequently subjected to clamping voltage
Solution Approach 1:
The protective diode is divided into multiple unit structures, each comprising a pn junction. By segmenting the protective diode into multiple units connected in series, the depletion layer spreading is suppressed and breakdown voltage reliability is improved while maintaining reasonable device area
Solution Approach 2:
Different regions of the protective diode are doped with different impurity concentrations to create localized properties. The first and third regions have different doping levels than the second and fourth regions, which suppresses depletion layer spreading and reduces leakage current in critical areas
2Area of stationary object
If the protective diode area is reduced, then the device size is smaller, but the electric field concentration on the pn junction increases leading to breakdown voltage failure
Solution Approach 1:
The protective diode employs a four-region structure with varying impurity concentrations where the second and fourth regions have lower doping levels than the first and third regions. This creates localized low-field regions that reduce electric field concentration and suppress depletion layer spreading, allowing area reduction without compromising reliability
Solution Approach 2:
The invention addresses electric field concentration by introducing a dimensional aspect through the vertical stacking of four semiconductor layers with different doping profiles. This layered structure distributes the electric field across multiple interfaces and regions, reducing peak field concentration even in compact areas
3Reliability
If the protective diode is frequently subjected to clamping voltage, then the protective function is effective, but localized deterioration of the pn junction occurs causing increased leakage current
Solution Approach 1:
The protective diode is segmented into multiple unit structures with distinct doping regions. This segmentation distributes the stress and deterioration effects across multiple junctions rather than concentrating them in a single pn junction, reducing localized deterioration and leakage current generation during frequent clamping operations
Solution Approach 2:
The four-region doping structure is designed beforehand to cushion against the harmful effects of frequent clamping voltage. The varying impurity concentrations create a structure that anticipates and mitigates depletion layer spreading and junction deterioration, preventing leakage current increase before it occurs
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 configuration suppresses the spreading of the depletion layer, reduces the area of the protective diode, and flattens the pn junction surface, thereby enhancing reliability by minimizing leakage current and preventing breakdown voltage failure.
Implementation Method 1
a protective diode that protects a surge voltage
Implementation Method 2
suppresses a spreading of a depletion layer
Data Source
Figure 1(a)~1(b)
Figure 2~3
Figure 4(a)~4(c)
AI summary
A protective diode (101) has a basic structure (103) including an n+ layer (11), an n- layer (10), a p+ layer (12), and an n- layer (10) in this order. A p-type layer forming the protective diode (101) is the p+ layer (12) with high impurity concentration. Therefore, the spreading of a depletion layer is suppressed and it is possible to reduce the area of the protective diode (101). In addition, phosphorus ions with a large diffusion coefficient are implanted to form the n- layer (10) with low impurity concentration in the polysilicon layer (9) forming the protective diode (101). A heat treatment is performed at a temperature of 1000°C or higher to diffuse the phosphorus ions implanted into the polysilicon layer (9). Therefore, the impurity profile of the n- layer (10) in the depth direction can be uniformized in the depth direction. As a result, a pn junction surface between the p+ layer (12) with high impurity concentration and the n- layer (10) with low impurity concentration is substantially perpendicular to the main surface of the substrate and it is possible to suppress the concentration of the electric field on the pn junction between the p+ layer (12) and the n- layer (10).