LDMOS Drain Isolation Diode Circuit for Substrate Injection
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Solution Overview
Problem
In system-on-a-chip (SOC) applications with inductive loads, negative potential during switching leads to significant injection current into the substrate, disturbing adjacent circuits and affecting their operation.
Innovation Solution
The implementation of diode circuits, specifically Schottky diodes and PN junction diodes, coupled between the drain region and the isolation structure of laterally diffused metal oxide semiconductor (LDMOS) field effect transistors (FETs), which reduces or eliminates current injection into the substrate by maintaining the isolation structure potential even when the drain potential goes negative.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the drain region is directly connected to the isolation structure, then the device structure is simple, but significant injection current flows into the substrate during switching, disturbing adjacent circuits
Solution Approach 1:
A diode circuit is introduced as an intermediary component between the drain region and the isolation structure. This diode circuit controls the current flow path, allowing normal operation current to pass while blocking injection current from entering the substrate during switching events, thereby eliminating the harmful effect without complicating the overall device structure
2Adaptability or versatility
If the drain potential is allowed to go negative during switching, then the device can handle inductive loads, but this causes significant current injection into the substrate
Solution Approach 1:
The diode circuit serves as a protective intermediary that decouples the drain region from the isolation structure during negative potential events. When the drain goes negative due to inductive load switching, the diode blocks current flow to the isolation structure, preventing substrate injection and protecting adjacent circuits while still allowing the drain to experience the necessary negative potential for proper inductive load operation
3Ease of manufacture
If no diode circuit is used, then the manufacturing process is simple, but current injection disturbs adjacent circuit blocks
Solution Approach 1:
The diode circuit is integrated into the existing device structure using standard semiconductor fabrication techniques. The added components and processing steps are minimal and compatible with conventional manufacturing flows, allowing the harmful current injection effect to be eliminated without substantially increasing manufacturing complexity or cost
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 solution effectively reduces or eliminates current injection into the SOC substrate, thereby minimizing disruption to adjacent circuit blocks and improving the operational stability of SOC systems with inductive loads.
Implementation Method 1
The diode circuit includes a Schottky diode
Implementation Method 2
The diode circuit includes a PN junction diode
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
Embodiments of semiconductor devices (200, 600, 700, 1100, 1300) and driver circuits (110) include a semiconductor substrate (210, 610, 710, 1110, 1310) having a first conductivity type, an isolation structure (including a sinker region (222, 622, 722, 1122, 1322, 1610, 1710) and a buried layer (220, 620, 720, 1120, 1320)), an active device within an area (230, 630, 730, 1130, 1330, 1520, 1620, 1720, 1820) of the substrate contained by the isolation structure, and a diode circuit (160). The buried layer is positioned below the top substrate surface (212, 612, 712, 1112, 1312), and has a second conductivity type. The sinker region extends between the top substrate surface and the buried layer, and has the second conductivity type. The active device includes a drain region (236, 636, 736, 1136, 1336) of the second conductivity type, and the diode circuit is connected between the isolation structure and the drain region. The diode circuit may include one or more Schottky diodes (346, 446, 546, 1245, 1445) and/or PN junction diodes (846, 946, 1046, 1246, 1446, 1447). In further embodiments, the diode circuit may include one or more resistive networks (410, 510, 910, 1010) in series and/or parallel with the Schottky and/or PN diode(s).