Basic characteristics and detailed explanation of MOS field effect sub-threshold effect

MOS field effect sub-threshold effect

The subthreshold effect is also called the weak inversion effect. So far, we have assumed that when the voltage applied to the MOS tube gate exceeds the threshold voltage, the surface is inverted and the channel is formed immediately. This is called It is a strong inversion approximation. When using the strong inversion approximate model to calculate the threshold voltage, the semiconductor surface potential ф  is equal to the Fermi potential ф 1< /span>Double (ф=2ф 1). According to the strong inversion approximate model, the drain-source output current ID and VGS The relationship of is shown by the solid line in Figure 1.4-5. In fact, the weak inversion area produces a current ID, that is, when ф=2ф 1(VGSVT), it has begun to conduct electricity, which is called the subthreshold effect or weak inversion effect.

The dashed line (curve) in Figure 1.4-4 reflects the relationship between the classic strong inversion approximate model and the weak inversion model. The weak inversion model considers VGS<VT, the conduction has started, and the drain-source conductanceID The relationship between  and VGS is an exponential relationship. MOS field effect sub-threshold effect. When ID is accompanied by VGS The exponential increases until it crosses the solid line describing the strong inversion model at a certain point (the voltage corresponding to this point is ). This It means that when , ID and VGS is an exponential relationship; and when , the relationship is linear. After considering the weak inversion effect, you can define a turn-on voltage. Its value is

where nL is the correction factor of weak inversion turn-on voltage, about 1.5～3.

After considering the weak inverse effect, when , the drain-source current equation is (see reference [35] for detailed derivation)

式中

a is the correction factor for short channel effect. This means that the drain-source current ID is indexed with VGS in weak inversion Variety.

Contact: Mr. Zou

Contact number: 0755-83888366-8022

Mobile phone: 18123972950

QQ: 2880195519

Contact Address: 5C1, Block CD, Tianji Building, Tianan Digital City, Chegongmiao, Futian District, Shenzhen

Please search WeChat official account: "KIA Semiconductor" or scan the following picture to "Follow" official WeChat official account

Please "follow" the official WeChat account: provide MOS tube technical assistance