SEMICONDUCTOR DEVICE PHYSICS AND DESIGN

5.2. METAL INTERCONNECTS 217

Element Work function, φm(volt)

Ag, silver 4.26

Al, aluminum 4.28

Au, gold 5.1

Cr, chromium 4.5

Mo, molybdenum 4.6

Ni, nickel 5.15

Pd, palladium 5.12

Pt, platinum 5.65

Ti, titanium 4.33

W, tungsten 4.55

ELECTRON AFFINITY OF SOME SEMICONDUCTORS

Element Electron affinity, χ (volt)

Ge, germanium 4.13

Si, silicon 4.01

GaAs, gallium arsenide 4.07

AlAs, aluminum arsenide 3.5

MATERIAL RESISTIVITY

(μΩ-cm)

Aluminum (Al)

Bulk 2.7

Thin Film 0.2-0.3

Alloys, Δρ

per %Si +0.7%Si

per %Cu +0.3%Cu

Titanium (Ti) 40.0

Tungsten (W) 5.6

Ti-W 15-50

Gold (Au) 2.44

Silver (Ag) 1.59

Copper (Cu) 1.77

Platinum (Pt) 10.0

Silicides

PtSi 28-35

NiS 2 50

WORK FUNCTIONS OF SOME METALS

Table 5.1: Resistivities of some metals used in solid state electronics

lower, allowing the thin interconnect film to carry very high current densities, of the order of
(∼ 106 Acm−^2 ).

Example 5.1In this example we will study some important concepts in thin-film resistors,

which form an important part of semiconductor device technology. The resistors are often

made from polysilicon that is appropriately doped. In thin-film technology it is usual to

define sheet resistance instead of the resistance of the material. Consider, as shown in

figure 5.1b, a material of lengthL, widthW, and depthD. The resistance of the material is

R=

ρL

WD

=

ρL

A

(5.2.1)

As we have discussed in chapter 3, the resistivityρis given by

ρ=

1

neμ

(5.2.2)