Why are NMOS tubes more popular than PMOS tubes?

Time：2023-12-20　Reading：95

The first is in terms of performance:

The device area of a PMOS tube with the same driving capacity as an NMOS tube may be 2 to 3 times that of an NMOS tube, but the device area will affect the on-resistance and input and output capacitance, and these related parameters are easy to cause circuit delay.
Similarly, under the same size conditions, the on-resistance of the PMOS channel is larger than that of NMOS, so the on-loss of the switch will be larger than that of the NMOS tube.

In terms of channels, we can further elaborate:

The channel of NMOS is made up of N-type semiconductors, while the channel of PMOS is made up of P-type semiconductors. Because the electron concentration of N-type semiconductors is higher than that of P-type semiconductors, the electron mobility of NMOS is higher than that of PMOS, that is, under the same electric field, the electron speed in NMOS is faster than that in PMOS.
Here we need to mention that due to the difference in mobility, there is a difference in speed and channel on-resistance, and it is precisely this that the application range of PMOS tubes is limited.
In terms of process, the manufacturing difference between PMOS tubes and NMOS tubes is not large, and with the continuous progress of the process, this difference has become smaller and smaller.

So, why is the electron mobility of MOS higher than that of PMOS, and the electron velocity in NMOS faster than that of PMOS?

Let's briefly start with electron/hole mobility:
Electron mobility refers to the physical quantity of how fast an electron moves under the action of an electric field force.

Two semiconductor materials with the same electron concentration, under normal circumstances, the same voltage is applied at both ends, the larger the mobility of the semiconductor material, the faster the electron movement in it, the more electrons will pass through the unit time, that is, the greater the current.
Therefore, we can explain that the higher the electron mobility of the semiconductor material, the lower its resistivity, when passing through the same current, its loss will be smaller.
Hole mobility is the same as electron mobility, the higher the hole mobility, the smaller the loss.
However, in general (also mentioned above), the mobility of electrons is higher than that of holes.
That's because a hole is an electron vacancy, and the movement of a hole, essentially, is an electron moving from one hole to another hole.

This is where we come back to the differences in conductive channels between NMOS and PMOS.
MOS has only one type of carrier, an electron or a hole. Under the bias voltage, the inverse layer will be formed as a conductive channel, which is the migration path of carriers.
The MOS tube forms an N-type conductive channel during conduction, which means that electrons are used to conduct electricity. The conduction of the PMOS tube forms a P-type conductive channel, which is used to conduct electricity. Simple notes are as follows:
NMOS is an N-type channel and its carrier is an electron.
The PMOS is a P-type channel and the carrier is a hole.

In general, the electron migration rate is five to ten times that of the hole migration rate, and this multiple can be even higher depending on the material and structure and its own properties.
Because the mobility of electrons is higher than that of holes, the loss of NMOS tubes is much smaller than that of PMOS tubes when the volume size and doping are the same.
In addition to power consumption, electron/hole mobility also affects the speed of the device.

Cutoff frequency of an NMOS tube
The result shows that the cutoff frequency is proportional to the electron mobility.

Therefore, the higher the electron mobility, the higher the frequency at which the NMOS tube can operate.
When the Vgs voltage of NMOS changes at a high frequency, the thickness of the conductive channel will also change.
The change of this conductive channel is formed by the movement of electrons, and the faster the electron movement speed (in other words, the higher the electron mobility), the faster the conductive channel can respond to the change of Vgs, which involves the working principle of NMOS tubes.
This shows that the higher the electron mobility, the higher the operating frequency of the device.
The same goes for PMOS tubes.
In addition to the above aspects, there are other factors that choose NMOS tube more, such as price issues, PMOS on the market will generally be higher than the price of NMOS, this is because the market economy is composed of multiple factors, in the selection of MOS tube, NMOS is selected after comprehensive consideration of much more.

For the reasons why NMOS tubes are more popular in practical applications, a simple summary is made:
1. The channel on-resistance of NMOS is much smaller than that of PMOS, and the switching on-loss is smaller;
2. NMOS is an N-type channel and its carrier is an electron; The PMOS is a P-type channel and the carrier is a hole. The electron migration rate is faster than the hole migration rate, and NMOS has more advantages in loss and switching speed.
3. The current passing capacity of N-type MOS tube will be larger than that of PMOS;
4. Market price and other factors