LDMOS Threshold Voltage Control via JFET Segmentation
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Solution Overview
Problem
Lateral double diffused metal oxide semiconductor (LDMOS) devices face challenges in adjusting threshold voltage without additional reticles or increasing dopant concentration, leading to difficulty in turning off due to conductive substrate regions, which results in persistent on-state operation.
Innovation Solution
A semiconductor device comprising a lateral double diffused metal oxide semiconductor, a junction field effect transistor, and an inner circuit, where the second source of the junction field effect transistor is connected to the first gate, allowing for adjustable threshold voltage through micrometer-scale width adjustments of the second source, enabling selective turn-on and turn-off states without additional reticles or increased dopant concentration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the concentration of dopant in the substrate is increased to adjust the threshold voltage higher, then the threshold voltage is improved, but the electrical resistance of the substrate decreases making the device hard to turn off
Solution Approach 1:
The invention divides the control function into two separate components: the LDMOS device for power amplification and a JFET for threshold voltage control. The JFET is segmented as a distinct control element that can independently adjust the threshold voltage of the LDMOS without affecting the substrate's electrical resistance, thus resolving the contradiction between threshold voltage adjustment and turn-off capability.
Solution Approach 2:
The JFET acts as an intermediary device between the control circuit and the LDMOS device. It mediates the threshold voltage adjustment by controlling the gate voltage of the LDMOS through its own gate-source voltage, allowing precise threshold control without directly modifying the LDMOS substrate doping concentration, thereby preserving the substrate's resistance characteristics and turn-off capability.
2Measurement precision
If an additional reticle is used to implant different dopant for adjusting threshold voltage, then the threshold voltage adjustment is achieved, but the manufacturing cost increases significantly
Solution Approach 1:
The JFET serves multiple functions: it acts as a threshold voltage adjustor, a control element, and a gate driver for the LDMOS device. This multi-functionality eliminates the need for additional reticles and complex ion implantation processes, as the JFET can be integrated into the existing manufacturing process without requiring separate doping steps or additional photomasks.
Solution Approach 2:
The invention merges the threshold voltage control function with the JFET structure, combining what would traditionally require separate reticle-based ion implantation into a single integrated device. The JFET's gate region is formed using the same photomask as other device regions, consolidating multiple functions into one manufacturing process and reducing overall manufacturing complexity and cost.
3Power
If the LDMOS device is designed as depletion mode with conductive substrate region, then the device has high operating bandwidth and output power, but the device remains always on and is difficult to turn off
Solution Approach 1:
The invention introduces dynamic control of the LDMOS device through the JFET. The JFET's gate-source voltage can be dynamically adjusted to control the LDMOS gate voltage, enabling the device to transition between on and off states. This dynamic control mechanism allows the LDMOS to maintain its depletion mode characteristics for high power operation while adding the capability to be turned off when needed.
Solution Approach 2:
The control circuit incorporating the JFET provides feedback control to the LDMOS device. The JFET monitors and adjusts the gate voltage of the LDMOS based on operating conditions, enabling precise control of the device state. This feedback mechanism ensures the LDMOS can be reliably turned off by controlling the JFET's gate-source voltage, which in turn controls the LDMOS gate voltage, resolving the always-on problem while preserving high power capability.
Data Source
AI summary
A method for operating a semiconductor device including a lateral double diffused metal oxide semiconductor (LDMOS) with a first source, a common drain and a first gate, a junction field effect transistor (JFET) with a second source, the common drain and a second gate wherein the second source is electrically connected to the first gate and an inner circuit electrically connected to the first source is provided. The first source provides the inner circuit with an inner current to generate an inner voltage by means of the lateral double diffused metal oxide semiconductor, and the lateral double diffused metal oxide semiconductor turns off when the inner voltage is elevated substantially as high as the first gate voltage.