AN1506 - APPLICATION NOTE

4/14

The source mask does not need to be aligned within the strip itself; the only critical parameter is the

width of the strip (see figure 1), which depends on the equipment resolution. As can be argued from the

above description, the process benefits in a reduced number of feature sizes since it is now only

dependent on a single feature size, and higher packing densities can be obtained in comparison to the

conventional cell-geometry process. The new process is also named Extremely High Density (EHD)

referring to the possibility of getting devices with very high equivalent cell densities. Figure 3 compares

the obtainable channel perimeter density and thus the current density of the two structures.

Figure 3. Channel perimeter density comparison of cell-based and strip-based structures

4. STATIC AND DYNAMIC BEHAVIOR OF THE NEW DEVICE.

The resulting MOSFET device of the strip-based process shows very interesting characteristics:

extremely high packing density and low on-state resistance, rugged avalanche characteristics, and less

critical alignment steps. First of all we have selected the device STB80NF55, which was the candidate

for the actual application in an AC drive. The drive is described with more details in the next section. The

main electrical quantities of the component are summarized in Table 1.

Table 1. STB80NF55 Main Electrical Characteristics

A preliminary characterization in a dc chopper working on inductive load has been done. Looking for the

specific application supplied at a dc bus of 24V, several commutation tests (turn on and turn off) have

been done at this voltage while the current assumed a variable value. The energy losses in such

conditions are reported in figure 4. Linear dependence of the energy versus the switched current is

evident both for the turn on and turn off transients.

[m

Ω]

[V]

[nC]

Qsw

[nC]

Qgd

[nC]

trr

[nS]

Qrr

[nC]

Irr

[A]

Package

6.5

55

180

90

66

80

245

6.4

Minimum feature size [µm]

Cell-based layout

Strip-based layout

30

25

20

15

10

87

65

4

3

2

1