Why Trench Schottky rectifiers are the preferred choice

When it comes to any system, to achieve the most efficient design we try to utilize the most ideal solution possible. Compared to their planar counterparts, Trench Schottky rectifiers take us much closer to that ideal solution.

We are continually pushing our electronic systems to be ever more efficient. For many systems and specifically power conversion circuits, the planar Schottky barrier diode has been a design mainstay for a long time. However, planar diodes impose a trade-off in key performance characteristics such as forward voltage drop and leakage current. Similarly, in EMC-sensitive applications, traditional Schottky diodes are far from the ideal lossless and instantaneous rectifier solution we would love to use.

The ideal rectifier

An ideal rectifier should have a low forward voltage drop, a high reverse blocking voltage, zero leakage current and low parasitic capacitance. But when it comes to realizing this in real-life, compromises must be made.

For example, certain metals can be used to minimize the voltage drop across the metal-semiconductor interface but only at the expense of a higher leakage current. Or if the drift region is made thicker to achieve a higher reverse blocking voltage, then the advantage of a low voltage drop across the junction can disappear. Traditionally, this has limited the reverse blocking voltage of Schottky rectifiers to well below 200 V.

Etching trenches into silicon

One challenge then is to increase reverse voltage without increasing leakage current. A limitation of a planar Schottky is that the equi-potential lines tend to be crowded close to the metal electrode and not the substrate, which can lead to early breakdown when the critical electrical field is exceeded near the surface. By etching trenches into the silicon and filling them with polysilicon, effectively depletes the drift region in the reverse direction and flattens the electrical field profile along the drift region.

 

Equi-potential lines in a planar Schottky rectifier and in a Trench Schottky rectifier in reverse direction

That means our Trench Schottky rectifier family achieves a well-balanced trade-off between Vf and IR. Compared to equivalent planar diodes, the Trench devices have a wider safe operating area. With robustness against thermal runaway, this makes them ideal in applications which experience higher ambient temperatures.

An extra RC-element in the Trench Schottky rectifier circuit provides another benefit. It gives better EMC performance than planar Schottky diodes, therefore Trench rectifiers may be more suitable in EMC-sensitive applications.

All-in-all, Trench Schottky rectifiers are the preferred choice

By combining Schottky with Trench technology, the latest Trench Schottky rectifiers bring the performance benefits many applications demand. Trench Schottky diodes deliver a better trade-off between forward voltage drop and the leakage current. They also have excellent EMC performance together with robustness against thermal runaway effects.

It is only when considering parasitic capacitance that designers need to take some care. Per unit area, the total parasitic capacitance of a Trench Schottky rectifier is higher than its planar counterpart. So, if a design features high switching losses then a planar Schottky may still be the best choice despite their other drawbacks. However, Trench rectifiers are certainly the favorable choice in applications where the majority of losses are due to forward voltage drop or leakage current.

Reza Behtash

Reza Behtash

Reza received his diploma degree in electrical engineering in 1999 from the technical University of Hamburg. He then spent four years as a research fellow at DaimlerChrysler research institute in Ulm working on GaN HEMTs and MMICs, and subsequently received his PhD from the Ulm University. Reza continued working on GaN technologies for power amplifiers while at the Ferdinand-Braun-Institut für Höchstfrequenztechnik in Berlin and during his time at United Monolithic Semiconductors (UMS). For the past eight years, as part of the Application Marketing team of Nexperia in Hamburg, his main focus has been on discrete planar and Trench Schottky rectifiers in automotive applications.