TrenchMOS or Trenchgate MOS

- overview or tutorial about the basics and essential details of the TrenchMOS or Trench Gate MOS field effect transistor an electronics component used in many applications to give higher power performance than traditional FETs

The TrenchMOS technology provides a significant improvement over previous power MOS technologies. This new form of power MOSFET is an electronics component which uses a new structure to provide a more direct and hence more efficient path for the current flow within the semiconductor device.

The TrenchMOS technology is an MOS "trench" style technology developed by Philips Semiconductors, now NXP which provides high levels of performance in terms of current density and low "ON" resistance. Although many manufacturers have their own forms of "trench" technology, TrenchMOS is the process that is manufactured and marketed by NXP.

The TrenchMOS devices offer electronics designers a choice of lower heat dissipation for the same size chip, a higher current handling capability from the same sized chip, or a smaller chip with the same dissipation. When choosing electronics components, TrenchMOS is a semiconductor technology that ahs plenty to offer when power MOSFET applications are needed.

TrenchMOS structure

TrenchMOS uses a vertical structure for the FET device. This has the advantage that it provide a structure in which a much shorter channel can be fabricated. As the current only flows through a relatively small area, resistance values can be high reducing the efficiency of the device.

TrenchMOS uses a vertical structure as shown below. From this it can be seen that this form of semiconductor device has the source is at the top of the device, and the drain is at the bottom. Instead of flowing horizontally as in the standard FET, current in this device flows vertically.

TrenchMOS field effect transistor structure
TrenchMOS field effect transistor structure

TrenchMOS has differences to other forms of vertical MOS semiconductor device structures. Rather than using the more established V-groove structure, a different trench format is used. With TrenchMOS FET technology, the gate is formed by etching a trench in the semiconductor structure which then has an insulating oxide layer added and then filled with polysilicon. The resulting structure is more optimally configured for the operation of a power MOSFET, where the depth of the structure is of vital importance to the operation and the resistance. This results in the on resistance being considerably reduced when compared to other FET electronics components.

The low resistance of the TrenchMOS FETs means that heat sinks are not required in many instances, enabling these devices to be made in surface mount packages for easy assembly on printed circuit boards, i.e. SOT223 and SOT404 (equivalent to D2PAK). The Rds(on) values comprise 8, 14, 18 and 24 milli-Ohm and a choice of 5V or 10V operational drive voltage, all with a peak voltage load tolerance of up to 55V. These devices also have built-in ElectroStatic Discharge protection of up to 2kV to protect during handling and assembly.

TrenchMOS applications

There are many applications for TrenchMOS devices. They allow such a device, i.e. in any portable electrical product that requires voltages of less than 100V to be switched on and off, but the most significant area is in automotive. Here there are three main uses on which Philips is focussing their use:

  1. Provide an alternative to relays that the automotive industry wants to replace as, being electro-mechanical, they are not as reliable as solid state switches.

  2. Achieve low resistances values of typically around 8 milli-Ohms using TrechMOS semiconductor. This can enable two conventional 15 milli-Ohm devices used in parallel (a typical technique used to achieve low resistance values) to be swapped for one device, thereby saving PCB space.

  3. TrenchMOS FET semiconductor devices enable electronics circuits to be made much smaller, again saving in cost and PCB space

In addition to these applications, TrenchMOS FET devices are incorporated in many integrated circuit chips.

By Ian Poole

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