MIS Protective Structure for Semiconductor Sensors
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Solution Overview
Problem
Ion-sensitive field-effect transistors (ISFETs) are vulnerable to electrostatic discharges and electrochemically unfavorable operating conditions due to the exposure of their gate insulator, and existing protective structures like p-n junctions and capacitors are inadequate in preventing leakage currents and polarity inversions.
Innovation Solution
A monolithic Metal Insulator Semiconductor (MIS) structure is integrated on the same substrate as the semiconductor sensor, comprising a doped region, an epitactic layer, an insulating layer, and a metal layer, which forms a protective diode that switches from high-impedance to low-impedance state to prevent damage, with adjustable layer thicknesses and materials to optimize performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional p-n junctions are used as protective structures, then protection against electrostatic discharges is provided, but leakage current increases and measurement precision deteriorates
Solution Approach 1:
The patent changes the fundamental parameters of the protective structure by transitioning from a p-n junction design to an MIS (Metal-Insulator-Semiconductor) structure. This parameter change enables the protective function to be achieved with significantly reduced leakage current, thereby maintaining measurement precision while providing ESD protection.
Solution Approach 2:
The protective structure employs a composite MIS configuration combining metal, insulator, and semiconductor layers. This composite structure integrates the protective functionality against electrostatic discharges while maintaining electrical characteristics suitable for precise potentiometric measurements, resolving the contradiction between protection and measurement accuracy.
2Reliability
If capacitor elements are used as protective structures, then protection against electrostatic discharges is provided, but alternating current conduction occurs and protection against polarity inversion becomes ineffective
Solution Approach 1:
The patent transforms the protective structure from a capacitive design to an MIS-based design, changing the electrical parameters to achieve both DC protection (against ESD and polarity inversion) and AC blocking capability. This parameter change eliminates the harmful alternating current conduction while maintaining protective functions.
Solution Approach 2:
The MIS protective structure acts as a sacrificial element that can absorb and dissipate electrostatic energy and protect against polarity inversion, effectively replacing the need for more complex protective circuits that would be vulnerable to AC conduction and polarity issues.
3Measurement precision
If the gate insulator is exposed in the channel area for ion-sensitive detection, then sensitivity to measuring medium is improved, but vulnerability to electrostatic damage increases
Solution Approach 1:
The patent introduces an MIS protective structure as an intermediary element between the ion-sensitive gate insulator and the external environment. This intermediary structure provides electrostatic protection while allowing the gate insulator to remain exposed for ion-sensitive detection, thus resolving the contradiction between sensitivity and vulnerability.
Solution Approach 2:
The protective function is segmented into a separate MIS structure that is integrated alongside the ion-sensitive transistor. This segmentation allows the sensor element to maintain its ion-sensitive exposed gate insulator while the separate MIS structure handles the electrostatic protection, enabling both functions to operate independently and effectively.
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
The MIS structure significantly reduces leakage currents and provides effective protection against electrostatic discharges and polarity inversions while maintaining high sensitivity, with adaptable electric selectivity and quick response, ensuring the semiconductor sensor's stability and accuracy.
Implementation Method 1
an insulating layer, wherein the insulating layer is disposed between the semiconducting layer and the metal layer and electrically insulates same
Implementation Method 2
which forms a protective diode that switches from high-impedance to low-impedance state to prevent damage
Data Source
AI summary
A protective structure for a semiconductor sensor integrated in a semiconductor substrate for use in a state that is in direct contact with a measuring medium has a semiconducting layer that is applied to the semiconductor substrate, a metal layer and an insulating layer. The insulating layer is disposed between the semiconducting layer and the metal layer and electrically insulates same.