Biochip Back Side Illumination Photodiode Structure
Solution Overview
Problem
Conventional biochips with front side illumination photodiode structures suffer from reduced light sensitivity due to light absorption by metal wiring lines and are prone to increased dark current and circuit interference during surface treatment and biochemical reactions.
Innovation Solution
A biochip with a back side illumination photodiode structure that collects light directly from the bottom surface of the wafer, avoiding metal wiring lines and preventing circuit interference, thereby enhancing light sensitivity and maintaining photodiode characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a front side illumination photodiode structure is used, then the photodiode can be manufactured with standard processes, but light sensitivity is degraded due to absorption by metal wiring lines
Solution Approach 1:
The patent inverts the conventional photodiode structure by placing the light-receiving surface on the back side of the substrate rather than the front side. This allows light to enter the photodiode from the back, completely avoiding absorption by the metal wiring lines that are located on the front side, thereby resolving the contradiction between manufacturability and light sensitivity
Solution Approach 2:
The patent transitions from a two-dimensional planar structure where light enters from the front to a three-dimensional structure where light enters from the back through the substrate. This dimensional change allows light to bypass the metal wiring lines that obstruct the front side, achieving both high light sensitivity and compatibility with standard manufacturing processes
2Reliability
If plasma surface treatment is applied to the biochip layer, then bio-material attachment is improved, but dark current of photodiodes increases
Solution Approach 1:
The patent divides the substrate into functionally independent sides: the front side for biochip layer formation and plasma treatment, and the back side for light reception by photodiodes. This segmentation isolates the photodiodes from the plasma treatment process, allowing plasma to be applied for improved bio-material attachment without generating dark current in the photodiodes
Solution Approach 2:
The substrate acts as an intermediary that separates the plasma treatment zone (front side) from the photodiode zone (back side). This intermediary structure allows plasma to treat the biochip layer surface without directly exposing the photodiodes to plasma, thereby preventing dark current generation while maintaining effective bio-material attachment
3Reliability
If the biochip layer is formed on the interlayer dielectric, then circuit protection is achieved, but solutions infiltrate through the dielectric causing circuit problems
Solution Approach 1:
The patent extracts the light-receiving function from the front side (where circuits and dielectric layers are located) and places it on the back side of the substrate. This extraction removes the photodiodes from the potential infiltration path of solutions, allowing the biochip layer to be formed on the interlayer dielectric for circuit protection without risking solution infiltration into circuits
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
Significantly improves light sensitivity and prevents circuit deterioration during manufacturing and biochemical reactions by directly collecting light at the bottom surface of the photodiodes, ensuring stable and high-sensitivity biochip performance.
Implementation Method 1
an image sensor with a back side illumination photodiode structure which collects light from the back side of a wafer of the biochip in order to improve capability of sensing light emitted from reaction regions of the biochip
Data Source
Figure 1~2
AI summary
A biochip (200) having an image sensor with a back side illumination photodiode structure includes: a biochip layer (200a); and an image sensor layer (200b) attached to one surface of the biochip layer and configured to sense light with biochemical reaction information, which is emitted from the biochip layer, wherein the image sensor layer includes a plurality of light sensing parts (PD1,PD2,PD3) which receive the light directed toward a back side of a wafer.