Chapter 2 semiconductor basic Devices

Summary

1. Diode, transistor, and FET (master their external characteristics and main parameters)
2. Understanding the physical structure of Semiconductors

I. Diode

1. Characteristic Curve

Unidirectional conductivity is positive, that is, forward conduction, and the flow of current is from p type to N Type

2. Main Parameters (taking two specific diodes as an example)

 

	rectifying 1n4001	switch type 1n4148
maximum forward current	1.0a	200mA
reverse breakdown voltage	50 V	75 v
reverse current	5μa	25na
maximum wage frequency	3 kHz	1 MHz
reverse recovery time	...	4ns

3. Application Example

① Limiting circuit (limiting the negative half-axis of the input signal)

U1 is the input voltage waveform, while U2 is the output voltage waveform, which limits the negative half axis of the input signal.

② Dynamic Features

Where:

Us is the input voltage and its frequency is 1000 kHz;

The diode corresponding to U2 is 1n4004 (for a rectifying diode), and its frequency is 3 kHz, indicating that 3000 switching times can be performed within 1 second, and its waveform cannot be changed normally.

The diode corresponding to U1 is 1n4148 (switched diode), and its frequency is 1 MHz. It indicates that 1000000 switching times can be performed within 1 second, and its waveform can be changed normally.

③ Voltage Regulator diode circuit main parameters (stable voltage uz Stable Current iz maximum stable current izm)

Among them, u1 = 12 V is the input voltage, but may change, even if the change, because the voltage regulator diode is in the reverse breakdown area, so it has a regulator, but the regulator is required. For the voltage regulator diode above, the voltage regulator value is determined. It is 5.6 V. The operating current of the Voltage Regulator diode is generally 5mA, and the maximum operating current is 82mA.

The above three figures calculate the minimum values of resistance R and RL in the circuit when the voltage regulation is met.

 

Ii. semiconductor transistor

1. Structure of a three-level pipe

① Three zones: the emission zone, the base zone, and the Collector zone lead to three Poles from three zones: collector C base pole B emitter pole E

② Two PN Knots: power generation and electric Junction

③ Text symbol of the transistor: vt

④ Internal structure characteristics of the transistor

	Doping Concentration	Area Thickness	PN junction area
Base Zone	Low	Thin
Launch Zone	High: the doping concentration is much greater than that in the base zone and collector zone.	Thick
Power Supply Zone	Medium	Thick
Electric Junction			Large
Launch knot			Small

2. Transistor classification (this is only divided by the internal basic structure)

3. Three access methods for Transistor

4. Transistor characteristic curve:

I input feature curve

A curve that reflects the relationship between the input current IB and the input voltage UBE. It uses the output voltage UCE as a reference.

Generally, the launch voltage of the transistor that starts to increase significantly is called the conduction voltage. At room temperature, the conduction voltage of the silicon tube is about 0.6 ~ The on-going voltage of 0.7 V and GE tube is 0.2 ~ 0.3 V.

II Output Characteristic Curve

It reflects the curve of the relationship between the output current IC and the output voltage UCE. It takes the input current IB value as a reference and is divided into three zones:

① Cut-off zone: Both pn are in reverse bias. At this time, the output voltage of the tube pressure drop UCE is almost the power supply voltage.

② Amplification zone: the positive deviation of the emission junction and the reverse deviation of the collector junction. The output current IC of the transistor in the amplification zone is only controlled by the input current IB, and has little to do with the output voltage UCE.

③ Saturation zone: Both pn are in positive bias. When the output voltage UCE <input voltage UBE, the output current IC is no longer controlled by the input current IB. The UCE value of the output voltage when the transistor is saturated is called the saturation pressure drop, which is recorded as UCEs. The saturation pressure drop of the Low-Power silicon tube is 0.3 V.

5. Two Functions of the transistor:

① "Amplification": When the transistor is in a magnification area, it has the effect of current amplification and can be used in analog circuits.

② "Switch": When the transistor is in the saturation and cut-off areas, it is equivalent to closing and disconnecting the circuit. It has both switching characteristics and can be applied to the pulse digital circuit.

6. Main Parameters of the transistor

The parameters of the transistor can be used as a reference for circuit design and proper use of the device. The following figure shows two parameters:

3. field effect transistor

1. Introduction: a transistor is a device that uses input current to control output current.Current ControllerThe FET is a device that uses the input voltage to generate an electrical field effect to control the output current.Voltage controller. Compared with the transistor, it has high input impedance, low noise, good thermal stability, low power consumption, simple manufacturing process, etc.AdvantagesEasy to implementIntegration.

2. Category of FET

End-type FET		Insulated Gate-type FET
N-Channel	P-Channel	Enhanced		Depletion type
		N-Channel	P-Channel	N-Channel	P-Channel

3. Structure and graphics Of The FET (taking the nd-channel enhanced insulation gate FET as an example)

Note:

① It is a low impurity concentrationP-type Silicon WaferAs a substrate, twoN-zone, which is very close to each other and has a high doping concentration,Two electrodes, called the source Pole s and the drain electrode D, are extracted respectively. A thin insulation layer is formed on the wafer surface, and an aluminum metal film is made on the insulation layer as the gate G. There are three intermittent lines between the D pole and the S pole, which are expressed as enhanced (if the continuous line is expressed as depletion type), and B is the substrate lead, which is generally connected with the source pole S, the arrow indicates the n-channel in the inner direction, and the P-channel in the reverse direction.

② Because the gate is insulated from other electrodes and silicon wafers, it is called an insulating grating-type Fet. It is also made of metal (conductor), oxide (insulator) and a silicon wafer (Semiconductor) doped with a small amount of impurities.

4. principle diagram of MOS tube (taking the n-channel enhanced insulation gate FET as an example)

5. characteristic curves of MOS tubes (taking nchannel-enhanced insulation gate FET as an example)

I Transfer Characteristic Curve

① The Transfer Characteristic Curve refers to the relationship between the drain current ID and the grid source voltage UGS when the drain source voltage UDS is a fixed value.

② Because the input current ig of the FET is almost 0, the input feature is not required.

③ The Transfer Characteristic Curve clearly shows the control function of grid source voltage on drain current.

II Output Characteristic Curve

① The Output Characteristic Curve refers to the relationship between the drain current ID and the drain source voltage UDS when UGS is a fixed value.

② The output characteristic curve is a family of curves, which can be divided into three areas, as shown in:

6. Main Parameters of the FET (taking the nd-channel enhanced insulation gate FET as an example)

① Enable voltage utn (GS): When the leakage source voltage UDS is constant, the enhanced MOS tube begins to generate the gate source voltage UGS with the drain current ID. UGS is an important parameter for enhanced Fet. It is a positive value for the n-Channel FET and a negative value for the p-Channel FET.

② GM refers to the ratio of UGS of the gate source input signal to the drain current ID caused by UDS when the leakage source voltage UDS is set, it is an important parameter that indicates the grid source voltage UGS controls the size of the drain current ID.

③ Drain pole breakdown voltage U (BR) ds refers to the maximum voltage allowed to be added between the drain source poles. If the actual voltage value exceeds this parameter, the pnend reverse breakdown will occur.