In depth analysis of the working principle of MOS transistor

As an important electronic device, the working principle of MOS transistor plays a crucial role in the field of electronics. The following will provide a detailed analysis of the working principle, semiconductor structure and working principle, importance, and future development and application prospects of MOS transistors.

1、 Using VGS to control induced charges

Taking N-channel enhanced MOSFET as an example, its working principle is to use VGS to control the amount of "induced charge". When manufacturing pipes, a large number of positive ions are generated in the insulation layer through the process, so that more negative charges can be induced on the other side of the interface. These negative charges connect the high permeability impurities in the N region, forming a conductive channel. Even when VGS=0, there is still a large drain current ID. When the gate voltage changes, the amount of induced charge in the channel also changes, and the width of the conductive channel also changes accordingly. Therefore, the drain current ID will change with the change of gate voltage.

Specifically, when VGS is greater than the threshold voltage Vth, the MOS transistor enters a conducting state. At this point, the positive ions in the insulation layer interact with the electrons in the substrate, forming a conductive channel. The number of electrons in the channel is directly proportional to VGS, that is, the higher the VGS, the more electrons in the channel, the wider the conductive channel, and the larger the drain current ID. On the contrary, when VGS is less than Vth, the MOS transistor is in a cut-off state, the number of electrons in the channel decreases, and the drain current ID approaches zero.

2、 Control DS on/off through GS terminal voltage

MOS transistor controls the on/off state between DS by controlling the voltage at the GS terminal. For example, in the simplest circuit, connect the battery pack, light bulb, and switch with wires. When the switch is closed, the light bulb lights up (ignoring the positive and negative connections). This is the principle behind the working schematic connection of MOS transistors.

Specifically, when the voltage VGS at the GS terminal is greater than the threshold voltage Vth, the MOS transistor conducts, the current path between the drain D and the source S is opened, and the circuit conducts. When VGS is less than Vth, the MOS transistor is turned off and the circuit is disconnected. The characteristic of voltage controlled on-off makes MOS transistors widely used in electronic circuits.

3、 Depletion layer under zero gate voltage

When uGS is equal to 0V, the g electrode and the substrate b electrode (s electrode and b electrode are directly short circuited together) cannot generate an electric field, thus unable to form an electronic region, also known as a depletion layer. The drain source connection is equivalent to two back facing transistors, and even if voltage is applied between the S and D terminals, no current will be generated.

The depletion layer is an important region in MOS transistors, and its width is related to VGS. When VGS is greater than the threshold voltage Vth, the depletion layer disappears and a conductive channel is formed; When VGS is less than Vth, the depletion layer width increases and the conductive channel disappears. Therefore, controlling VGS can achieve control over the conduction and cutoff of MOS transistors.

4、 Semiconductor Structure and Working Principle

Taking the semiconductor structure of MOS transistor as an example, the two blue regions are N-type semiconductors, which are doped with pentavalent phosphorus in pure silicon crystal. At this time, the outermost layer of this phosphorus atom has an extra free electron. Because the free electron carries a negative charge, it is called N-type semiconductor, and N is taken from the first letter of negative.

In N-type semiconductors, there are more free electrons and better conductivity. In MOS transistors, N-type semiconductors are used as substrates to form P-type semiconductors with high permeability impurities through doping. In P-type semiconductors, there are a large number of holes and poor conductivity. When VGS is greater than the threshold voltage Vth, free electrons in N-type semiconductors interact with holes in P-type semiconductors to form a conductive channel.

5、 The importance of MOS transistors

MOS transistors are widely used in modern electronic technology, and their efficient control performance and low power consumption characteristics make them play an important role in integrated circuits, power management, and other fields. Here are a few application examples:

Integrated circuit: MOS transistor is the basic component for implementing integrated circuit functions such as logic gates and memory.

Power management: MOSFETs are used in power management circuits for switch control, improving power efficiency.

Dynamic Random Access Memory (DRAM): MOSFETs are the core components of DRAM memory cells.

Analog circuit: MOS transistors are used in analog circuits for functions such as amplification and switching.

6、 Future Development and Application Prospects

With the continuous advancement of electronic technology, the performance of MOS transistors is also constantly improving, and it is expected to achieve more widespread applications in high-performance computing, artificial intelligence and other fields in the future. Here are some development trends:

High speed and high-performance MOS transistors: By optimizing semiconductor materials, device structures, etc., the switching speed and transmission rate of MOS transistors can be improved.

Low power MOS transistor: While maintaining high performance, reduce the power consumption of MOS transistors to meet green environmental requirements.

Intelligent MOS transistor: Combining artificial intelligence technology to achieve intelligent control of MOS transistors and improve circuit performance.

New MOS transistor: Explore new semiconductor materials and device structures, develop new MOS transistors, and expand application fields.

In short, as an important device in the field of electronics, MOS transistors have significant importance in terms of their working principles, performance, and application prospects. With the continuous development of technology, MOS transistors will play a key role in more fields.