Hard and Soft Composition Lead Zirconate Titanate Thin Films Deposited by Pulsed Laser Deposition
- PDF / 347,683 Bytes
- 5 Pages / 414.72 x 648 pts Page_size
- 82 Downloads / 215 Views
Biaxial tensile and compressive stresses were applied to the films using the apparatus in Figure 1. A PZT film on a 3" Pt coated Si substrate was sandwiched between two viton O-rings and clamped on top of a bored out aluminum round. The cavity behind the wafer could either be evacuated by a ltm roughing pump or pressurized by a gas bottle/regulator combination to apply compressive or tensile biaxial stress to the wafer. At a pressure of 15psi, the maximum stress at the center of the wafer was calculated to be 140MPa using large deflection plate theory [5].
Screws
O-rings
Pressure Gauge
Figure 1. Illustration of stress apparatus RESULTS Film Facts Figure 2 shows a glancing angle x-ray diffraction patterns of hard and soft composition films grown at room temperature and post deposition annealed at 650'C for 60 seconds. Films grown at room temperature typically exhibited partial (100) preferred orientation, but films grown at 400'C exhibited random orientation. Typical film thickness was -4000 A, and a typical surface grain size was -0.1 gim.
hard soft
Figure 2. Glancing angle x-ray diffraction patterns of hard and soft films grown at room temperature and post deposition crystallized
208
ElectricalProperties Electrical properties for both hard and soft films were found to be similar. Typical hysteresis loops for both types of films are shown in figure 3. Both compositions show similar coercive field and remanent polarization values. Dielectric constants of films in this study ranged between 1100 and 1500 with no trend of higher or lower values based on composition. The loss tangent, however, was found generally to be lower for soft films than for hard films. For the two films in figure 3, the loss tangents were 0.01 and 0.03 for soft and hard compositions, respectively. 80
60
.. ........... ..
. ...............
.. .
........
.
.... ......
PZT-8,
60 -40
"- 0
--_ -
---- --------
----
-20 -40 " -
:
-60 106
-40 106
-
20 106 0.0 10° Electric Field (Vim)
-20 106
40106
-
60 106
Figure 3. Hysteresis loops for hard and soft composition PZT thin films The observance of similar coercive field is notable because it is a prime indicator of domain wall mobility. Similar coercive field leads to the conclusion that the domain walls have comparable mobility in the hard and soft composition films. The increased loss tangent in hard composition films also supports this conclusion. In bulk hard and soft PZT, the loss is higher in soft PZT due to the contribution of domain wall motion, and lower in hard PZT for the lack of domain wall
motion [1]. The trend seen in these films is the opposite. If the contribution of domain walls were
similar in both cases, other contributions must be considered to explain the differences. An important contribution to consider is conduction. Since conduction in undoped PZT is generally p type, hard (acceptor) doped materials would be expected to exhibit increased conduction due to an increase in hole concentration. Soft PZT on the other hand, which is donor doped, should
Data Loading...
