Thick-Oxide Input Transistor for Low-Flicker Noise Preamplifier
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Solution Overview
Problem
Deep sub-micron CMOS technologies face challenges with high flicker noise in preamplifiers due to the use of oxy-nitrides for thin gate oxides, which affects noise performance, especially in capacitive transducers like miniature condenser microphones.
Innovation Solution
A deep sub-micron MOS integrated circuit die with a preamplifier featuring a thick-oxide transistor as the input stage, which reduces flicker noise by increasing gate dimensions and using nitrided silicon-dioxide for the gate oxide, optimizing gate capacitance and impedance for low-noise signal amplification from condenser microphones.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If thin-oxide transistors are used in deep sub-micron CMOS technology, then device density and integration are improved, but flicker noise increases dramatically due to oxy-nitride gate material
Solution Approach 1:
The patent changes the gate oxide thickness parameter from thin (typical for deep sub-micron CMOS) to thick (8-40 nm), which fundamentally alters the noise characteristics of the transistor. This parameter change reduces flicker noise by increasing the gate oxide thickness, thereby reducing carrier trap density effects while maintaining compatibility with deep sub-micron fabrication processes
Solution Approach 2:
The patent applies local quality by using thick-oxide transistors specifically for the input stage of the preamplifier where low noise is critical, while other stages can use standard thin-oxide transistors. This allows optimization of the noise-critical region without compromising overall device density and integration benefits
2Object-generated harmful factors
If gate oxide thickness is increased to reduce flicker noise, then noise performance is improved, but gate capacitance per unit area decreases
Solution Approach 1:
The patent creates an asymmetric transistor design where the gate oxide thickness is significantly larger than typical deep sub-micron transistors. This asymmetric approach to oxide thickness allows the input stage transistor to have different electrical characteristics (lower capacitance, lower noise) compared to standard transistors in the same process
Solution Approach 2:
The patent addresses the capacitance reduction by transitioning to a different dimensional approach - using increased gate width to compensate for reduced capacitance density. The thick-oxide transistor is designed with larger gate dimensions (e.g., 600 μm width) to achieve the necessary total capacitance value despite the lower capacitance per unit area
3Strength
If thick-oxide transistors are used for high voltage operation, then voltage tolerance is improved, but device geometry must be increased
Solution Approach 1:
The patent performs preliminary action by pre-defining the thick-oxide transistor with optimized dimensions during the design stage. The gate width and length are carefully selected to provide the necessary voltage tolerance and noise performance before fabrication, allowing the transistor to be operated at higher voltages without requiring further adjustments
Data Source
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AI summary
The present invention relates to a condenser microphone assembly comprising a condenser microphone transducer comprising adjacently positioned diaphragm and back-plate members having an air gap there between. Moreover, the assembly comprises a deep sub-micron MOS integrated circuit die comprising a preamplifier comprising a first signal input terminal for receipt of electrical signals generated by the condenser microphone transducer. The first signal input terminal is operatively coupled to an input stage of the preamplifier, said input stage comprising a thick-oxide transistor. The present invention further relates to a deep sub-micron MOS integrated circuit die comprising a thick-oxide transistor-based preamplifier.