Abstract:
Planar-spiral piezoelectric-unimorph-actuators, that deflect out-of-their-plane, were
modelled, designed and fabricated. A range of other planar piezoelectric-device designs
has also been made. These include spokes, multi-arms, plates and swastikas. All these
devices consisted of a mechanical support in the plane with a piezoelectric layer
deposited on top. Impedance spectra demonstrated that a fabricated device was
piezoelectrically active. Finite-element (FE) models of straight and spiral piezoelectric-
unimorph-actuators were constructed. The mechanical stiffness of the spiral-beam was
increased with the curvature of the beam; consequently, the inner coils exhibited virtually
no deflection and appeared to be redundant. The advantage of the spiral-actuators is that
they allow large actuator lengths to be contained compactly without the loss of
mechanical stiffness.
Fabrication of the above devices necessitated the development of new fabrication
technologies. The active-piezoelectric and mechanical-support were a lead zirconate
titanate (Pb(Tii_XZrx)O3
-
PZT) thick-film and a-platinised-silicon-wafer respectively. Vias
were opened in the PZT with wet etching, and this was completed without damaging the
back electrode. Powder blasting allowed any 2-dimensional-shape to be cut into the
device wafer. Devices were released from the Si support with deep-reactive-ion-etching
(DRIE).
The PZT thick films were fired with a Cu20-PbO eutectic additive. Pb and Cu were
considered to dope on A and B lattice sites (of PZT) respectively, when the PZT was
sintered at high oxygen-partial-pressure (p02). The electrical conductivity of PZT thick
films was increased when they were sintered at low P02, and this was moderated by the
presence of Cu' as an acceptor ion.
A lead-platinum intermetallic and lead silicate glass phase simultaneously formed under
sintering conditions of low pot, and this simultaneous formation, was accounted for by a
six-stage mechanism. Step 1, residual C in the thick film reduces PbO to Pb followed by
step 2 where Pb diffuses into the Pt back electrode. In step 3, Pt3Pb formation occurs in
the intermetallic layer followed by step 4 in which PtPb forms. Step 5 occurs with
saturation of the intermetallic layer as Pb continues to diffuse from the thick film. There
is additional diffusion of Pb into the underlying Si substrate. Finally step 6 occurs at some
later point, when P02 has risen, Pb is oxidised to PbO, and Si is oxidised to Si02. PbO and
Si02 can flux to form PbSiO3
The glass was found to undermine film/substrate adhesion.