Page 108 - An Introduction to Microelectromechanical Systems Engineering

Passive Micromachined Mechanical Structures 87

Silicon
Adhesive

Silicon
Outlet
(a)

Inlet
Silicon Outlet

(b)
Figure 4.4 Illustration of side-shooter nozzles: (a) nozzles formed by orientation-dependent
etching of grooves, wafer bonding, and dicing [8], and (b) nozzle formed by DRIE and wafer
bonding. (After: [9].)

such as bumps and trenches (see Figure 4.5). The mandrel material must be electri-
cally conducting to enable electroplating and have sufficient adhesion to the metal
being plated but allow the metal to be peeled off after plating [10]. For example, the
materials system used by Hewlett-Packard for early-generation inkjet orifice plates
is electroplated nickel on a stainless steel mandrel: stainless steel has a thin epitaxial
oxide layer on it that allows electrical conduction but does not form a strong bond
to the plated nickel. Photoresist or some other insulator is patterned on the mandrel

Photoresist
Mandrel

1. Make mandrel, pattern photoresist

Metal

2. Electroplate metal

Orifice

3. Peel metal off
Figure 4.5 Illustration of an electroformed nozzle process.