RC Low-Pass Filter Integration in Single Polysilicon CMOS
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Solution Overview
Problem
The challenge in forming resistor-capacitor (RC) low-pass filters in integrated circuits is that many circuits are fabricated using a single polysilicon process flow, which lacks a load resistor layer or control gate layer, making it difficult to integrate additional polysilicon layers for RC filter formation.
Innovation Solution
An RC low-pass filter is formed using a single polysilicon process by utilizing a base region as a resistive electrode and a doped polysilicon layer for the upper electrode, with the capacitor dielectric layer being formed simultaneously with the gate dielectric layer, eliminating the need for additional polysilicon layers and simplifying the process integration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a double polysilicon process flow is used to form RC low-pass filters, then the filter can be formed with dedicated load resistor and control gate layers, but the process complexity increases and compatibility with single polysilicon CMOS processes is reduced
Solution Approach 1:
The patent merges the RC filter formation process with the standard CMOS fabrication process by using the same polysilicon layer that forms the transistor gate electrodes to also serve as the capacitor electrode and resistor elements. This eliminates the need for separate load resistor and control gate layers, thereby reducing process complexity while maintaining RC filter functionality.
Solution Approach 2:
The polysilicon layer is designed to serve multiple functions simultaneously: it acts as the gate electrode for MOSFETs, the capacitor electrode for the RC filter, and the resistive element for the RC circuit. This multi-functionality approach allows RC filter integration without requiring additional dedicated layers, resolving the contradiction between filter capability and process complexity.
2Reliability
If additional polysilicon layers are added for RC filter formation, then the filter structure can be properly formed, but the process integration difficulty increases
Solution Approach 1:
The patent combines the formation of the RC filter capacitor electrode with the formation of the transistor gate electrode into a single polysilicon deposition and patterning step. This merging of operations simplifies process integration by eliminating the need for additional polysilicon layers and reducing the number of fabrication steps required.
Solution Approach 2:
The RC filter structure is formed during the preliminary stages of CMOS fabrication, specifically during the polysilicon gate formation step, rather than requiring subsequent additional steps. This preliminary action approach integrates the RC filter into the base process flow without adding manufacturing complexity.
Data Source
AI summary
A process of forming an electronic device can include forming a capacitor dielectric layer over a base region, wherein the base region includes a base semiconductor material, forming a gate dielectric layer over a substrate, forming a capacitor electrode over the capacitor dielectric layer, forming a gate electrode over the gate dielectric layer, and forming an input terminal and an output terminal to the capacitor electrode. The input terminal and the output terminal can be spaced apart from each other and are connected to different components within the electronic device. A filter can include the base region, the capacitor dielectric layer, and the capacitor electrode. A transistor structure can include the gate dielectric layer and the gate electrode. An electronic device can include a low-pass filter and a transistor structure, such as an n-channel transistor or a p-channel transistor.