Counter-doped Varactor Structure for High Tuning Ratio
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Solution Overview
Problem
Existing varactor semiconductor devices face limitations in breakdown voltage, tuning ratio, and series resistance, where improving one factor often adversely affects the others, hindering their performance in applications requiring high capacitance variation and low AC losses.
Innovation Solution
The varactor diode structure is enhanced by incorporating a P+NPN structure with hyper-abrupt N doped regions and counter-doped P regions, optimizing the doping profile to increase the tuning ratio while maintaining or improving breakdown voltage and reducing series resistance, thereby enhancing the device's capacitance variation and quality factor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the device design is changed to improve the tuning ratio, then the capacitance variation increases, but the breakdown voltage or series resistance deteriorates
Solution Approach 1:
The patent applies local quality by creating a non-uniform doping profile within the semiconductor structure. Specifically, it uses a hyper-abrupt junction where the dopant concentration changes rapidly over a short distance, creating regions of different doping levels (lighter and heavier doped regions) within the depletion layer. This localized variation in doping quality allows the structure to achieve high capacitance modulation through the lighter doped region while the heavier doped region maintains structural integrity and breakdown voltage.
Solution Approach 2:
The patent employs parameter changes by precisely controlling the dopant concentration gradient in the hyper-abrupt junction. The doping profile is engineered to have a specific mathematical relationship where the concentration changes exponentially or hyper-abruptly rather than linearly. By adjusting the doping parameters (concentration, gradient, depth), the patent simultaneously optimizes the tuning ratio (capacitance variation) while maintaining adequate breakdown voltage and minimizing series resistance.
2Quantity of substance
If the device design is changed to improve the tuning ratio, then the capacitance variation increases, but the series resistance increases
Solution Approach 1:
The patent addresses series resistance by creating localized heavily doped regions at specific positions within the semiconductor structure. These heavier doped regions serve as conductive pathways that reduce series resistance, while the lighter doped regions maintain the high capacitance modulation capability. This spatial differentiation of doping quality allows simultaneous optimization of both capacitance variation and series resistance.
Solution Approach 2:
The patent effectively creates a composite doping structure within the single semiconductor crystal, combining regions of different doping concentrations (light and heavy) in a controlled manner. This composite approach allows the structure to exhibit both high capacitance modulation (from the hyper-abrupt junction with lighter doping) and low series resistance (from the strategically placed heavier doped regions), achieving properties that would be difficult to obtain with uniform doping.
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 significantly improves the tuning ratio at low applied voltages, useful for mobile communication devices, by adjusting the doping profile to maximize capacitance change without increasing series resistance, thus enhancing the varactor's performance in integrated oscillators and other communication devices.
Implementation Method 1
incorporating a P+NPN structure with hyper-abrupt N doped regions and counter-doped P regions, optimizing the doping profile to increase the tuning ratio
Implementation Method 2
The change in varactor capacitance with applied voltage comes about, for example, when the depletion region of a reverse biased junction widens and narrows with the applied voltage
Data Source
AI summary
An improved varactor diode (40) is obtained by providing a substrate (41) having a first surface (43), in which are formed a P+ region (53, 46) proximate the first surface (43), a first N region (54, 45) located beneath the P+ region (53, 46), an N well region (56, 44) located beneath the first N region (54, 45) and a first P counter-doped region (55) located between the first N region (54, 45) and the N well region (56, 44), thereby forming an P+NPN structure for the varactor diode. In some embodiments, a second P-type counter-doped region (59) is provided within the N-well region (56, 44) so as to reduce the N doping concentration within the N well region (56, 44) but without creating a further PN junction therein. The net doping profile (52) provides varactor diodes (40) having a larger tuning ratio than varactors (20) without such counter-doped regions. By interchanging N and P regions an N+PNP varactor is obtained.