DMOS Transistor? | DMOS Structure, Advantages & Applications

DMOS is a physical structure to make a metal oxide semiconductor transistor. In it the D stand for double diffusion. In one polarity diffusion is done through formation of hole in the oxide and the other polarity of carrier diffusion is done. At the surface this diffusion produces the three areas of alternating polarity carriers that is used in making metal oxide semiconductor transistors only the middle channel is very short and thin.

Diffuse metal oxide semiconductor transistor (DMOS Transistor)

DMOS Transistor

Structure of DMOS

The structure of DMOS is given below .The length of channel is controlled by the junction depth produced by the positive side and p-type diffusions underneath the gate oxide. Length is also the distance between the n-p junction and the p-n substrate junction. The length of the channel can be made to a smaller distance of about 0.5 µm. This process is similar to the base width of a double-diffused bipolar transistor. When high positive voltage is applied to the gate but this voltage is less than threshold voltage[>VTH], it will cause the conversion of the p-substrate region underneath the gate to n- type substrate, and the n-type region inversion layer that will act as a conducting channel and electrons flow from source to drain.

DMOS Structure

In it the n-type substrate is very lightly doped. This will make enough space for the expansion of the depletion region between the p-type diffusion region and the n-type drain region. Due to this, the breakdown voltage will higher between the drain and source.

Advantages of DMOS transistor

The advantages of the DMOS transistor include following properties;

  • High input impedance
  • High current gain
  • High power gain
  • No thermal runway problems


  • Automobile control electronics
  • Inkjet print heads
  • Power supplies
  • Radio frequency
  • transportation technology


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