Low Parasitic Capacitance Schottky Diode Using Polysilicon Island
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Solution Overview
Problem
Integrated circuits, particularly those for RF and MS functions, face reduced quality factors due to capacitive coupling with resistive substrates, leading to parasitic capacitance and leakage in Schottky diodes, which degrades their performance and introduces noise.
Innovation Solution
A Schottky diode is fabricated using a polysilicon island on a shallow trench isolation (STI) pad, with metal/silicide contacts, isolating the island from the semiconductor substrate to reduce parasitic capacitance and leakage, and incorporating a ground contact to minimize noise, all within a standard CMOS processing flow with minimal additional steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Schottky diodes are made using conventional methods, then they can be produced in standard CMOS processing, but parasitic capacitance and leakage to the substrate increase, degrading diode performance
Solution Approach 1:
An n-type polysilicon island is introduced as an intermediary structure between the Schottky diode and the CMOS substrate. This polysilicon island is entirely isolated from the substrate by shallow trench isolation (STI), serving as a mediator that eliminates parasitic capacitance and leakage paths while allowing the diode to be formed using standard CMOS processing techniques
Solution Approach 2:
The diode structure is segmented into distinct components: the Schottky diode formed on the polysilicon island surface, the polysilicon island itself as a separate layer, and the STI isolation structure. This segmentation allows each component to be optimized independently and facilitates integration with standard CMOS processes
2Reliability
If the polysilicon island is entirely isolated from the substrate using STI, then parasitic capacitance and leakage are reduced, but the number of processing steps increases
Solution Approach 1:
The formation of the polysilicon island and the STI isolation structure is merged with the standard CMOS processing sequence. The polysilicon island is formed simultaneously with the CMOS polysilicon gate, and the STI is integrated into the existing isolation architecture, allowing multiple functions to be achieved without adding significant processing complexity
3Object-affected harmful factors
If a third ground contact is added to reduce noise, then noise is minimized, but device complexity increases
Solution Approach 1:
The n-type polysilicon island serves a dual function: it acts as the electrical connection element for the Schottky diode and simultaneously provides a path for the optional third ground contact to reduce noise. The polysilicon island essentially serves itself by providing both the electrical connection and the noise reduction functionality through its inherent properties and positioning
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 approach significantly reduces parasitic capacitance and leakage, maintains low production costs, and enhances thermal isolation, enabling the diode's use in sensitive applications like optical and infrared radiation detection without increasing production expenses.
Implementation Method 1
A first metal/silicide contact formed on the lightly-doped region provides the Schottky junction
Implementation Method 2
Parasitic capacitance and leakage from the polysilicon island to the underlying semiconductor substrate is greatly reduced by entirely isolating the polysilicon island from the semiconductor substrate using the STI pad
Implementation Method 3
the radiation impinging on the diode raises it temperature and the temperature change is detected by the diode in reverse bias which serves as a sensitive temperature dependent resistor
Implementation Method 4
The Schotkky on STI benefits from better thermal isolation as compared to 'bulk' diodes, and hence can be used as a bolometer detector for optical and infrared radiation
Data Source
AI summary
A low parasitic capacitance Schottky diode including a lightly doped polycrystalline silicon island that is formed on a shallow trench isolation (STI) pad such that the polycrystalline silicon island is entirely isolated from an underlying silicon substrate by the STI pad. The resulting structure reduces leakage and capacitive coupling to the substrate. Silicide contact structures are attached to lightly-doped and heavily-doped regions of the polycrystalline silicon island to form the Schottky junction and Ohmic contact, respectively, and are connected by metal structures to other components formed on the silicon substrate. The STI pad, polycrystalline silicon island, and silicide/metal contacts are formed using a standard CMOS process flow to minimize cost. A bolometer detector is provided by measuring current through the diode in reverse bias. An array of such detectors comprises an infrared or optical image sensor.