CdTe Radiation Detector UBM Electrode Structure
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Solution Overview
Problem
The degradation of metal electrode layers during the formation of UBM layers in CdTe or CdZnTe substrates for radiation detectors results in insufficient electric characteristics, particularly due to the formation of high-resistance phosphorus concentration layers when using electroless nickel plating.
Innovation Solution
A radiation detector UBM electrode structure body is developed with a Pt or Au electrode layer formed by electroless plating, followed by an Ni layer and a Pd and Au layer formed by sputtering, with specific thicknesses to prevent degradation and achieve low resistance UBM layers, and an optional insulating film is applied to improve adhesion and reduce leak currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If electroless nickel plating is used to form UBM layers, then the UBM layer formation is easy, but high-resistance phosphorus concentration layers are formed resulting in insufficient electric characteristics
Solution Approach 1:
The UBM layer is divided into multiple layers: a bottom UBM layer (Ni-P alloy) formed by electroless plating for ease of manufacture, and an upper UBM layer (Ni) formed by sputtering for low resistance. This segmentation allows each layer to fulfill different functions - the bottom layer provides manufacturing ease while the upper layer ensures electric characteristics.
Solution Approach 2:
The patent uses a composite structure combining Ni-P alloy and Ni layers, where the Ni-P alloy layer (containing 3-10 mass% P) provides ease of formation through electroless plating, while the pure Ni layer formed by sputtering provides low resistance and good electric characteristics.
2Ease of manufacture
If UBM layers are formed on metal electrode layers, then solder joining is enabled, but the metal electrode layers degrade resulting in insufficient electric characteristics
Solution Approach 1:
A protective film (SiO2, SiN, or organic resin) is formed on the metal electrode layer before forming the UBM layer. This preliminary protective action prevents degradation of the metal electrode layer during subsequent UBM layer formation processes while still enabling solder joining capability.
Solution Approach 2:
The protective film acts as an intermediary between the metal electrode layer and the UBM layer, preventing direct contact and degradation during manufacturing processes. This intermediary layer preserves the electric characteristics of the metal electrode while allowing the UBM layer to be formed for solder joining.
3Strength
If thin UBM layers are formed to maintain adhesion, then adhesion is improved, but resistance increases
Solution Approach 1:
The UBM structure is segmented into a thin bottom Ni-P alloy layer (50-200 nm) for maintaining adhesion to the substrate, and a thicker upper Ni layer (200-500 nm) for providing low resistance. This segmentation allows the thin layer to maintain adhesion while the thicker layer compensates for resistance.
Solution Approach 2:
The composite UBM structure combines a thin Ni-P alloy layer optimized for adhesion with a thicker pure Ni layer optimized for low resistance, achieving both good adhesion and low resistance simultaneously through material composition optimization.
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 solution effectively suppresses the degradation of metal electrode layers, achieving sufficient electric characteristics and improved adhesion, while preventing the formation of high-resistance phosphorus concentration layers, thus enhancing the performance of radiation detectors.
Implementation Method 1
a Pt or Au electrode layer formed directly on the substrate by electroless plating
Implementation Method 2
an Ni layer formed directly on the Pt or Au electrode layer by sputtering
Data Source
Figure 1(a)~1(b)
Figure 2
Figure 3
AI summary
The present invention provides a radiation detector UBM electrode structure body and a radiation detector which suppress the degradation of metal electrode layers at the time of formation of UBM layers and achieve sufficient electric characteristics, and a method of manufacturing the same. A radiation detector UBM electrode structure body according to the present invention includes a substrate made of CdTe or CdZnTe, comprising a Pt or Au electrode layer formed on the substrate by electroless plating, an Ni layer formed on the Pt or Au electrode layer by sputtering, and an Au layer formed on the Ni layer by sputtering.