pmos

Basic information

PMOS refers to an n-type substrate, p-channel, a MOS tube that carries current through the flow of holes

Full name: positive channel Metal Oxide Semiconductor

Alias: positive MOS

Metal oxide semiconductor field effect (MOS) transistors can be divided into two categories: N-channel and P-channel, P-channel silicon MOS field effect The transistor has two P+ regions on the N-type silicon substrate, called the source and the drain. There is no conduction between the two electrodes. When a sufficient positive voltage is applied to the source (the gate is grounded), the N-type under the gate The silicon surface presents a P-type inversion layer, which becomes a channel connecting the source and drain. Changing the gate voltage can change the hole density in the channel, thereby changing the resistance of the channel. This MOS field effect transistor is called a P-channel enhancement type field effect transistor. If there is no gate voltage on the surface of the N-type silicon substrate, the P-type inversion layer channel already exists, and with a proper bias voltage, the resistance of the channel can be increased or decreased. Such MOS field effect transistors are called P-channel depletion field effect transistors. Collectively referred to as PMOS transistors.

P-channel MOS transistors have low hole mobility. Therefore, when the geometric size of the MOS transistor and the absolute value of the working voltage are equal, the transconductance of the PMOS transistor is smaller than that of the N-channel MOS transistor. In addition, the absolute value of the threshold voltage of the P-channel MOS transistor is generally high, and a higher operating voltage is required. The voltage and polarity of its power supply are not compatible with bipolar transistors-transistor logic circuits. Because of the large logic swing, long charging and discharging process, and small transconductance of the device, PMOS has a lower operating speed. After the emergence of NMOS circuits (see N-channel metal-oxide-semiconductor integrated circuits), most of them have been developed by NMOS circuits. Replace. However, due to the simple process and low price of PMOS circuits, some medium-scale and small-scale digital control circuits still use PMOS circuit technology.

MOSFET has three pins, generally G, D, and S. When a control signal is added between G and S, the conduction and cut-off between D and S can be changed. PMOS and NMOS are completely similar in structure, the difference is the doping type of the substrate and source and drain. Simply put, NMOS is formed on a P-type silicon substrate by selective doping to form N-type doped regions as the source and drain regions of NMOS; PMOS is formed on an N-type silicon substrate by selective doping The P-type doped region serves as the source and drain region of the PMOS. The distance between the two source and drain doped regions is called the channel length L, and the effective source and drain region dimension perpendicular to the channel length is called the channel width W. For this simple structure, the source and drain of the device are completely symmetrical. Only in the application can the specific source and drain be confirmed according to the direction of the source and drain current.

The working principle of PMOS is similar to that of NMOS. Because PMOS is an N-type silicon substrate, the majority carriers are electrons, the minority carriers are holes, and the doping type of the source and drain regions is P-type. Therefore, the working condition of PMOS is that the gate is relative to the source. A negative voltage is applied to the pole, that is, negatively charged electrons are applied to the gate of the PMOS, and movable positively charged holes and a depletion layer with fixed positive charges are induced on the substrate, regardless of the existence of silicon dioxide The number of positive charges induced in the substrate is equal to the number of negative charges on the PMOS gate. When it reaches the strong inversion type, under the action of the drain-source voltage that is negative relative to the source terminal, the positive charge holes at the source terminal reach the drain terminal through the conductive P-type channel, forming a source-drain current from the source to the drain. Similarly, the more negative the VGS (the greater the absolute value), the smaller the on-resistance of the channel, and the greater the value of the current.

Like NMOS, the working area of ​​the turned-on PMOS is also divided into unsaturated zone, critical saturation point and saturation zone. Of course, regardless of NMOS or PMOS, when the inversion channel is not formed, it is in the cut-off region. The voltage condition is:

VGS

|VGS|>|VTP (PMOS )|,

It is worth noting that the VGS and VTP of PMOS are both negative.

PMOS integrated circuit is a device suitable for applications in low-speed and low-frequency fields. The PMOS integrated circuit is powered by -24V voltage.

MOS field-effect transistors have very high input impedance and are easy to directly couple in the circuit, making it easy to make large-scale integrated circuits.

Comparison of the characteristics of various field effect transistors

In the International Electronic Device Conference (IEDM) in December 2004, it was stated that the dual stress liner (DSL) method resulted in NMOS and PMOS The effective drive current increases by 15% and 32%, respectively, and the saturation drive current increases by 11% and 20%, respectively. The hole mobility of PMOS can be increased by 60% without using SiGe, which has become the focus of other strained silicon research.

Chemicals

PMOs are periodic mesoporous organosilicas, mesoporous silicon-based organic-inorganic hybrid materials. It is a material in which organic and inorganic components are hybridized in the pore wall at the molecular level. This type of material has many unique properties: the organic functional groups are evenly distributed in the pore wall and do not block the pores, which is conducive to the introduction and diffusion of guest molecules; The organic functional groups in the framework can adjust the physical and chemical properties of the material to a certain extent, such as mechanical properties, affinity/hydrophobicity; it can also realize the modulation of the functionality of the pores and pore walls at the same time. Because of this, PMOs have become a research hotspot in the field of materials science today.

In the early 1990s, reports of ordered mesoporous silica materials represented by M41S (Mobile composite of matter) and FSM (folded sheets mesoporous materi-al) set off the synthesis and synthesis of mesoporous materials. The upsurge of applied research. On the one hand, the emergence of ordered mesoporous materials breaks through the pore size limit of microporous materials (such as zeolites), and can be applied in the fields of organic macromolecules and biological macromolecules, catalytic conversion, etc.; on the other hand, mesoporous materials The pores of different orientations, different sizes and different degrees of connectivity in the material are ideal nanoreactors, which can be used to assemble and confine metal complexes and biological macromolecules, and oriented synthesis of nanoparticles. The original mesoporous material is composed of silicon oxide. In order to expand its application in different fields, researchers are committed to expanding the study of its pore wall composition, including heteroatom-doped mesoporous silicon oxide and mesoporous metal oxide. , Metals, sulfides, carbon, polymers, etc., as well as organic modification of mesoporous silica. Among them, organic modification is one of the most convenient and flexible ways to expand its application. For organic functionalized meso-L silica materials, there are mainly two types: surface-bonded and bridged organic-inorganic mesoporous materials. Surface-bound organic-inorganic mesoporous materials can introduce organic groups into the pores of the mesoporous material by post-grafting or co-condensation. The introduced organic groups can also derive new active centers through further chemical reactions. The active sites of surface-bound organic-inorganic mesoporous materials are relatively easy to access, and there are relatively many types of organic groups to choose from. However, the materials synthesized by this method have the disadvantages of uneven distribution of organic groups, occupying pore space and reducing pore volume. Bridged organic-inorganic mesoporous materials, referred to as PMOs (Periodic Mesoporous Organosilicas), refer to organic-inorganic mesoporous materials in which organic groups exist in the pore wall structure of the material.

Security operating system

PMOS dedicated mobile operating system based on the deep customization of YunOS.

Application in reverse protection circuit

PMOS is used in reverse protection circuit, and the voltage drop is smaller without the use of diodes, and there is less power dissipation. Regardless of a parasitic forward diode, it is completely useless. When the circuit is normally energized, GATE is connected to the 0 potential far lower than the D terminal, and the PMOS is completely conductive. When the power supply is reversed, the potential of GATE is much higher than the S terminal, and the PMOS is completely cut off.