Radiation Detector Preamplifier Layout for Lower Input Capacitance
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Solution Overview
Problem
Conventional radiation detectors suffer from increased noise and deteriorated energy resolution due to parasitic capacitance in the amplifying circuit, which is caused by the arrangement of components leading to larger input capacitance.
Innovation Solution
The amplifier is designed with a feedback capacitor configuration where a first conductive layer serves as the bonding pad and a second conductive layer is positioned below it, with an insulating layer in between, eliminating parasitic capacitance from wiring and reducing input capacitance by incorporating overlapping components on the semiconductor substrate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional component arrangement is used in the amplifying circuit, then the circuit is easy to manufacture, but parasitic capacitance increases leading to higher noise and deteriorated energy resolution
Solution Approach 1:
The bonding pad and feedback capacitor are merged into a single integrated structure. The first conductive layer serves dual functions as both the bonding pad for external connections and one electrode of the feedback capacitor, eliminating the need for separate wiring and reducing parasitic capacitance while maintaining ease of manufacture.
Solution Approach 2:
The feedback capacitor is nested within the bonding pad structure. The second conductive layer is positioned below the first conductive layer (bonding pad) with an insulating layer in between, creating a capacitor structure that is embedded within the existing bonding pad footprint, thereby reducing overall device complexity.
2Reliability
If wiring is added to connect the bonding pad and feedback capacitor, then the circuit functionality is improved, but parasitic capacitance increases leading to higher noise
Solution Approach 1:
The harmful wiring element is extracted and eliminated. The direct connection between the bonding pad and feedback capacitor electrode is achieved by making the bonding pad itself the capacitor electrode, removing the intermediate wiring that would introduce parasitic capacitance and noise.
Solution Approach 2:
The insulating layer serves as an intermediary between the first conductive layer (bonding pad) and the second conductive layer, enabling the formation of a feedback capacitor without requiring conductive wiring, thus preventing noise introduction while maintaining circuit functionality.
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 configuration reduces noise in the signal output and improves energy resolution in radiation detectors by minimizing input capacitance, enabling more accurate X-ray detection and analysis.
Implementation Method 1
a feedback capacitor connected in parallel to the amplifying circuit; the feedback capacitor is configured so that the insulating layer serves as a dielectric while the first conductive layer and the second conductive layer serve as a pair of electrodes
Implementation Method 2
the conventional preamplifier causes a parasitic capacitance between an interconnection layer below the bonding pad 74 and, for example, the substrate 77, and also between the metal wiring 75 and, for example, the substrate 77
Data Source
AI summary
In a preamplifier (amplifier) for the radiation detector, an interconnection layer connected to the bonding pad forms one electrode of a feedback capacitor. Since there is no wiring for connecting the bonding pad and capacitor, a parasitic capacitance caused by the wiring will not be generated. Moreover, the capacitor is arranged below the bonding pad with a conductive layer serving as the other electrode, so that the feedback capacitance of the capacitor is included in the parasitic capacitance between the interconnection layer and the substrate. Compared to the conventional case, an amount of capacitance corresponding to the parasitic capacitance caused by wiring and the feedback capacitance for the capacitor is reduced from the input capacitance. Thus, the input capacitance for the amplifying circuit is reduced.