MIS Capacitor Voltage Dependence Reduction in LCD Driver ICs
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Solution Overview
Problem
In the manufacturing of semiconductor integrated circuit devices, particularly in LCD driver IC chips, there is a challenge in reducing the voltage dependence of capacitors while maintaining cost competitiveness, as existing methods to minimize voltage dependence increase process costs.
Innovation Solution
The semiconductor integrated circuit device incorporates a semiconductor substrate with N-type and P-type low withstanding voltage well regions, where a P-channel type low withstanding voltage MISFET and an N-type medium withstanding voltage MIS capacitor are formed, with the N-type medium withstanding voltage well region acting as one capacitor electrode, and similarly, an N-channel type low withstanding voltage MISFET and a P-type medium withstanding voltage MIS capacitor are formed, utilizing polysilicon electrodes to reduce voltage dependence and enhance area efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing methods are used to minimize voltage dependence of capacitors, then voltage dependence is reduced, but process costs increase
Solution Approach 1:
The patent changes the voltage rating parameter of the capacitor from low withstanding voltage to medium withstanding voltage. This parameter change allows the capacitor to exhibit reduced voltage dependence while using a standard manufacturing process, thereby avoiding additional process costs. The medium withstanding voltage characteristic inherently provides better voltage independence compared to low withstanding voltage capacitors.
Solution Approach 2:
The patent uses the same N-type or P-type well region formation process for both the MISFET and the MIS capacitor. This multi-functional approach allows a single process step to create structures serving dual purposes: as the well region for the transistor and as one electrode for the capacitor, eliminating the need for separate expensive processes to achieve voltage independence.
2Area of stationary object
If area efficiency is enhanced through integrated capacitor design, then area efficiency improves, but device complexity increases
Solution Approach 1:
The patent merges the capacitor structure with the existing well region of the MISFET. Instead of creating a separate capacitor structure, the design combines the capacitor's electrode function with the well region that already exists for transistor operation. This merging achieves high area efficiency by utilizing shared structural elements.
Solution Approach 2:
The well region serves dual functions: as the active region for the MISFET and as one electrode for the MIS capacitor. This multi-functionality reduces the need for additional dedicated capacitor structures, thereby improving area efficiency without proportionally increasing device complexity.
Data Source
AI summary
In IC chips for display device driving, an operational amplifier is widely used in input and output circuits, and a capacitor in a medium withstanding voltage chip is used as a compensation capacitor. As for this product area, cost competitiveness is very important. Therefore, a MIS capacitor with good area efficiency is widely used. However, unlike a so-called varactor widely used in a VCO circuit, a characteristic of as small a voltage dependence of the capacitor as possible is used. Therefore, an additional process is added to reduce the voltage dependence of the capacitor, but there is a problem of an increase in process cost. A semiconductor substrate side capacitor electrode in a MIS capacitor within a first conduction type medium withstanding voltage chip used in an I/O circuit or the like on a semiconductor integrated circuit device is formed in a first conduction type low withstanding voltage well region.