U.S. patent application number 14/058912 was filed with the patent office on 2015-04-23 for piezoelectric element, piezoelectric actuator, piezoelectric sensor, hard disk drive, and ink-jet printer device.
The applicant listed for this patent is TDK CORPORATION. Invention is credited to Yasuhiro AIDA, Hiroshi CHIHARA, Kazuhiko MAEJIMA, Ryu OHTA, Hitoshi SAKUMA, Yoshitomo TANAKA.
Application Number | 20150109372 14/058912 |
Document ID | / |
Family ID | 52775346 |
Filed Date | 2015-04-23 |
United States Patent
Application |
20150109372 |
Kind Code |
A1 |
AIDA; Yasuhiro ; et
al. |
April 23, 2015 |
PIEZOELECTRIC ELEMENT, PIEZOELECTRIC ACTUATOR, PIEZOELECTRIC
SENSOR, HARD DISK DRIVE, AND INK-JET PRINTER DEVICE
Abstract
The displacement as an actuator or the sensitivity as a sensor
of a piezoelectric element can be increased and, in addition, the
electric power consumption can be reduced by providing a thin film
of potassium-sodium niobate, which is a perovskite type compound
represented by a general formula ABO.sub.3, as a piezoelectric
layer, wherein a crystal orientation of a crystal structure of
potassium-sodium niobate has in-plane fourfold symmetry as a whole
piezoelectric layer, where a first axis of rotational symmetry is a
thickness direction of the piezoelectric layer.
Inventors: |
AIDA; Yasuhiro; (Tokyo,
JP) ; OHTA; Ryu; (Tokyo, JP) ; TANAKA;
Yoshitomo; (Tokyo, JP) ; CHIHARA; Hiroshi;
(Tokyo, JP) ; SAKUMA; Hitoshi; (Tokyo, JP)
; MAEJIMA; Kazuhiko; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TDK CORPORATION |
Tokyo |
|
JP |
|
|
Family ID: |
52775346 |
Appl. No.: |
14/058912 |
Filed: |
October 21, 2013 |
Current U.S.
Class: |
347/68 ; 310/338;
310/358 |
Current CPC
Class: |
G01L 9/008 20130101;
B41J 2/14233 20130101; H01L 41/1873 20130101; H01L 41/0805
20130101; G01L 1/16 20130101; B41J 2202/03 20130101; H01L 41/316
20130101; B41J 2/045 20130101; H01L 41/0973 20130101 |
Class at
Publication: |
347/68 ; 310/358;
310/338 |
International
Class: |
H01L 41/08 20060101
H01L041/08; G01L 1/16 20060101 G01L001/16; B41J 2/045 20060101
B41J002/045; H01L 41/187 20060101 H01L041/187 |
Claims
1. A piezoelectric element characterized by comprising a thin film
of potassium-sodium niobate, which is a perovskite type compound
represented by a general formula ABO.sub.3, as a piezoelectric
layer, wherein a crystal orientation of a crystal structure of
potassium-sodium niobate in the piezoelectric layer has in-plane
fourfold symmetry as a whole piezoelectric layer, where a first
axis of rotational symmetry is a thickness direction of the
piezoelectric layer, and the thin film of potassium-sodium niobate
contains at least a tetragonal crystal.
2. The piezoelectric element according to claim 1, characterized in
that, in the piezoelectric layer, there is a second axis of
rotational symmetry, with respect to which the crystal orientation
of the crystal structure of potassium-sodium niobate has fourfold
symmetry and which is inclined from the thickness direction, in
addition to the first axis of rotational symmetry.
3. (canceled)
4. A piezoelectric actuator comprising the piezoelectric element
according to claim 1.
5. A piezoelectric sensor comprising the piezoelectric element
according to claim 1.
6. A hard disk drive comprising the piezoelectric actuator
according to claim 4.
7. An ink-jet printer device comprising the piezoelectric actuator
according to claim 4.
Description
BACKGROUND OF INVENTION
[0001] 1. Field of Invention
[0002] The present invention relates to a piezoelectric element by
using a thin film piezoelectric material, a piezoelectric actuator
and a piezoelectric sensor including the piezoelectric element, and
a hard disk drive and an ink-jet printer device provided with the
piezoelectric actuator.
[0003] 2. Background Art
[0004] In recent years, there is an increasing demand for a
piezoelectric material becoming lead-free and research on
potassium-sodium niobate ((K,Na)NbO.sub.3 (hereafter may be
referred to as KNN) has become active. It is believed that a
relatively high Curie temperature and good piezoelectric
characteristics are obtained by KNN among lead-free piezoelectric
materials and, therefore, KNN has been noted.
[0005] In addition, instead of bulk piezoelectric materials,
commercialization of a piezoelectric element by using a thin film
piezoelectric material has proceeded. Examples include
piezoelectric sensors taking advantage of a piezoelectric effect,
in which a force applied to a piezoelectric layer is converted to a
voltage, e.g., a gyro sensor, a pressure sensor, a pulse wave
sensor, a shock sensor, and a microphone, piezoelectric actuators
taking advantage of an inverse piezoelectric effect, in which a
piezoelectric layer is deformed when a voltage is applied to the
piezoelectric layer, e.g., a hard disk drive head slider and an
ink-jet print head, and a speaker, a buzzer, a resonator, and the
like taking advantage of the inverse piezoelectric effect in the
same manner.
[0006] In the case where a piezoelectric material is made into a
thin film, miniaturization of an element becomes possible,
applicable fields are expanded and, in addition, mass productivity
increases because many elements can be produced on a substrate in
one operation. Furthermore, there are many advantages in
performances, for example, the sensitivity is improved in the case
where a sensor is produced. [0007] [PTL 1] Japanese Unexamined
Patent Application Publication No. 2009-295786 [0008] [PTL 2]
Japanese Unexamined Patent Application Publication No. 2008-192868
[0009] [PTL 3] WO 2003-070641
SUMMARY OF INVENTION
[0010] However, a piezoelectric layer made from KNN has a problem
in that the piezoelectric constant is low and a large displacement
is not obtained easily when a piezoelectric element is produced as
compared with a piezoelectric layer by using a material containing
lead.
[0011] If the piezoelectric constant is low, a high voltage is
required to obtain a large displacement and a problem occurs in
that dielectric breakdown is induced or the reliability during
continuous operation is reduced.
[0012] It is stated that the technology described in PTL 1 can
improve the piezoelectric constant by allowing the ratio of the
out-of-plane lattice constant c of the KNN thin film to the
in-plane lattice constant a to fall within a predetermined range.
However, in this technology, the lattice constant is controlled by
controlling the stress of the thin film. Therefore, the value is
susceptible to the film formation condition and the film thickness,
and the reproducibility is low.
[0013] It is stated that the technology described in PTL 2 can
obtain good electrical characteristics (leakage characteristics and
piezoelectric characteristics) by using at least one type of
element selected from the group consisting of Pb, Ba, La, Sr, Bi,
Li, Na, Ca, Cd, Mg, and K as the A site element and using at least
one type of element selected from the group consisting of Ti, Zr,
V, Nb, Ta, Cr, Mo, W, Mn, Sc, Co, Cu, In, Sn, Ga, Zn, Cd, Fe, Ni,
and lanthanide elements as the B site element in perovskite type
oxides, which include KNN and which are represented by ABO.sub.3.
However, in the case where a KNN thin film in which K and Na are
employed as primary components of the A site and Nb is employed as
a primary component of the B site is used as a piezoelectric
element, sufficient electrical characteristics are not obtained
even when the above-described additives are added to the
above-described sites.
[0014] It is stated that the technology described in PTL 3 can
obtain good piezoelectric characteristics and leakage current
characteristics by using Pb as a primary component of the A site,
using Zr, Ti, and Pb as primary components of the B site, and
further specifying the proportion of Pb atom relative to the total
atoms in the B site to be 3% or more and 30% or less in a
piezoelectric, which has a perovskite type crystal structure
represented by ABO.sub.3. However, the film formation condition to
dispose Pb serving as a primary component in both the A and B sites
is limited considerably, and the reproducibility and the mass
productivity are poor. In addition, unfavorably, Pb is hazardous
and, therefore, an environment suitable for the use is limited.
[0015] The present invention has been made in consideration of the
problems included in the above-described related art and it is an
object to provide a piezoelectric element including a KNN thin film
and having a more improved piezoelectric constant.
[0016] The fact that a large displacement can be obtained refers to
that a high piezoelectric constant is provided. Therefore, the
element on the basis of a piezoelectric effect can be applied to
the use of, for example, a sensor having high sensitivity and an
element on the basis of an inverse piezoelectric effect can be
applied to the use of, for example, an efficient actuator which can
produce large vibration by a small voltage.
[0017] In order to achieve the above-described object, a
piezoelectric element according to the present invention is a
piezoelectric element including a thin film of potassium-sodium
niobate, which is a perovskite type compound represented by a
general formula ABO.sub.3, as a piezoelectric layer, wherein a
crystal orientation of a crystal structure of potassium-sodium
niobate in the above-described piezoelectric layer has in-plane
fourfold symmetry as a whole piezoelectric layer, where a first
axis of rotational symmetry is a thickness direction of the
above-described piezoelectric layer.
[0018] The crystal orientation of the crystal structure of the
piezoelectric layer is allowed to have in-plane fourfold symmetry
and, thereby, the piezoelectric constant of the piezoelectric layer
is improved and, in particular, the displacement in the plane
direction (31 direction) increases.
[0019] In the case where a voltage is applied in the thickness
direction of the piezoelectric layer, the movement of a domain wall
in addition to the lattice strain due to the piezoelectric effect
distributes to the expansion and contraction behavior in the plane
direction because the direction of the applied electric field and
the polarization direction are not parallel. The direction of the
domain walls can be aligned by allowing the crystal orientation of
the crystal structure of the piezoelectric layer to have in-plane
fourfold symmetry, and the displacement can be increased
effectively as compared with a piezoelectric element including a
piezoelectric layer having an in-plane asymmetric crystal
structure.
[0020] In the piezoelectric layer of the piezoelectric element
according to the present invention, preferably, there is a second
axis of rotational symmetry, with respect to which the crystal
orientation of the crystal structure of potassium-sodium niobate
has fourfold symmetry and which is inclined from the
above-described thickness direction, in addition to the
above-described first axis of rotational symmetry. Consequently,
the piezoelectric characteristics can be further enhanced.
[0021] The crystal orientation of the crystal structure with
respect to the second axis of rotational symmetry, which is present
while being inclined from the thickness direction of the
piezoelectric layer, is present in addition to the crystal
orientation of the crystal structure with respect to the first axis
of rotational symmetry, which is the above-described thickness
direction, so that the piezoelectric characteristics in a higher
voltage region are enhanced. The reason for this is considered that
the inclined 180.degree. domain is present and, thereby, a
rotatable domain remains when a high voltage is applied, and the
region contributes to displacement.
[0022] Preferably, the piezoelectric layer of the piezoelectric
element according to the present invention contains at least a
tetragonal crystal. Consequently, temperature dependence of the
piezoelectric characteristics can be reduced.
[0023] It is considered that in the case where an orthorhombic
crystal is present in the piezoelectric layer, when heating is
continued, transition to a tetragonal crystal occurs before the
Curie point (cubic crystal phase transition temperature) is reached
and, thereby, large temperature dependence is provided, although
the influence is not exerted on a portion which is originally a
tetragonal crystal.
[0024] A piezoelectric actuator according to the present invention
includes the piezoelectric element represented by the
above-described configuration. Specific examples of piezoelectric
actuators include a head assembly of a hard disk drive and a
piezoelectric actuator of an ink-jet printer head.
[0025] Meanwhile, a piezoelectric sensor according to the present
invention includes the piezoelectric element represented by the
above-described configuration. Specific piezoelectric sensors
include a gyro sensor, a pressure sensor, and a pulse wave
sensor.
[0026] In addition, in a hard disk drive and an ink-jet printer
device according to the present invention, the above-described
piezoelectric actuator is used.
[0027] The piezoelectric element according to the present invention
can improve the piezoelectric characteristics as compared with the
piezoelectric element including the conventional KNN thin film.
Meanwhile, the piezoelectric actuator and the piezoelectric sensor
according to the present invention can also improve the
piezoelectric characteristics. Therefore, high-performance hard
disk drive and ink-jet printer device can be provided.
BRIEF DESCRIPTION OF DRAWINGS
[0028] FIG. 1 is a configuration diagram of a piezoelectric element
according to an embodiment of the present invention.
[0029] FIGS. 2A and 2B are structural diagrams of piezoelectric
actuators according to the present invention.
[0030] FIGS. 3A to 3D are structural diagrams of piezoelectric
sensors according to the present invention.
[0031] FIG. 4 is a structural diagram of a hard disk drive
according to the present invention.
[0032] FIG. 5 is a structural diagram of an ink-jet printer device
according to the present invention.
[0033] FIG. 6 is a diagram of a diffraction pattern showing the
in-plain orientation property obtained by an XRD measurement of a
piezoelectric layer in a conventional piezoelectric element.
[0034] FIG. 7 is a diagram of a diffraction pattern showing the
in-plain orientation property obtained by an XRD measurement of a
piezoelectric layer in a piezoelectric element according to the
present invention.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0035] A preferred embodiment according to the present invention
will be described below in detail with reference to the drawings.
In this regard, in the drawings, the same or equivalent members are
indicated by the same reference numerals. Meanwhile, vertical and
horizontal relationships between positions are as shown in the
drawing. And the same explanations will not be provided.
[0036] (Piezoelectric Element)
[0037] FIG. 1 shows a piezoelectric element 100 according to the
present embodiment. The piezoelectric element 100 includes a
substrate 4, an insulating layer 6 and a first electrode layer 8
disposed on the substrate 4, a piezoelectric layer 10 disposed on
the first electrode layer 8, and a second electrode layer 12
disposed on the piezoelectric layer 10.
[0038] A silicon substrate exhibiting (100) face orientation can be
used as the substrate 4. The substrate 4 has, for example, a
thickness of 50 .mu.m or more and 1,000 .mu.m or less. In addition,
a silicon substrate exhibiting face orientation different from a
(100) face, a Silicon on Insulator (SOI) substrate, a quartz glass
substrate, a compound semiconductor substrate made from, for
example, GaAs, a sapphire substrate, a metal substrate made from,
for example, stainless steel, a MgO substrate, a SrTiO.sub.3
substrate, or the like can also be used as the substrate 4.
[0039] The insulating layer 6 is used in the case where the
substrate 4 is electrically conductive. A silicon thermal oxidation
film (SiO.sub.2), Si.sub.3N.sub.4, ZrO.sub.2, Y.sub.2O.sub.3, ZnO,
Al.sub.2O.sub.3, or the like can be used as the insulating layer 6.
In the case where the substrate 4 does not have electrical
conductivity, the insulating layer 6 may not be provided. The
insulating layer 6 can be formed by a sputtering method, a vacuum
evaporation method, a thermal oxidation method, a printing method,
a spin coating method, a sol-gel method, or the like.
[0040] The first electrode layer 8 is formed from, for example, Pt
(platinum). The first electrode layer 8 has a thickness of, for
example, 0.02 .mu.m or more and 1.0 .mu.m or less. The first
electrode layer 8 is formed from Pt and, thereby, the piezoelectric
layer 10 having high orientation property can be formed. Also, a
metal material, e.g., Pd (palladium), Rh (rhodium), Au (gold), Ru
(ruthenium), Ir (iridium), Mo (molybdenum), Ti (titanium), or Ta
(tantalum), or an electrically conductive metal oxide, e.g.,
SrRuO.sub.3 or LaNiO.sub.3, can be used as the first electrode
layer 8. The first electrode layer 8 can be formed by the
sputtering method, the vacuum evaporation method, the printing
method, the spin coating method, the sol-gel method, or the
like.
[0041] In the first electrode layer 8, preferably, the (100) face
or an orientation face parallel thereto, e.g., a (200) face or
(400) face, has in-plane fourfold symmetry with respect to the
thickness direction. The first electrode layer 8 having in-plane
fourfold symmetry with respect to the thickness direction can be
formed by, for example, the vacuum evaporation method.
[0042] The substrate temperature at this time is specified to be
preferably 800.degree. C. or higher and 1,000.degree. C. or lower.
Consequently, the first electrode layer 8 having higher orientation
property can be formed.
[0043] As for the material used for the first piezoelectric layer
10, for example, a thin film of potassium-sodium niobate is used,
which is a perovskite type compound and in which the crystal
orientation of the crystal structure of the (001) face has in-plane
fourfold symmetry, where the thickness direction is an axis of
rotational symmetry.
[0044] The piezoelectric layer 10 is formed through film formation
by the sputtering method, the vacuum evaporation method, the
printing method, the spin coating method, the sol-gel method, or
the like.
[0045] The crystal orientation of the crystal structure of the
piezoelectric layer 10 is allowed to have in-plane fourfold
symmetry and, thereby, the piezoelectric constant of the
piezoelectric layer 10 is improved and, in particular, the
displacement in the plane direction (31 direction) can be
improved.
[0046] In the piezoelectric layer 10, preferably, there is a second
axis of rotational symmetry, with respect to which the crystal
orientation of the crystal structure of potassium-sodium niobate
has fourfold symmetry and which is inclined from the
above-described thickness direction, in addition to the
above-described first axis of rotational symmetry in the thickness
direction. Consequently, there is a tendency that the piezoelectric
characteristics can be further enhanced.
[0047] Preferably, the piezoelectric layer 10 contains at least a
tetragonal crystal. Consequently, there is a tendency that
temperature dependence of the piezoelectric characteristics can be
reduced.
[0048] Preferably, the first electrode layer 8 is subjected to
reverse sputtering before film formation of the piezoelectric layer
10. Consequently, for example, there is a tendency that formation
of the thin film of potassium-sodium niobate, which is a perovskite
type compound and in which the crystal orientation of the crystal
structure of the (001) face has in-plane fourfold symmetry with
respect to the thickness direction can be facilitated, and there is
a tendency that the piezoelectric characteristics of the
piezoelectric element can be further enhanced.
[0049] Preferably, the piezoelectric layer 10 is formed in two
steps. There is a tendency that, in the piezoelectric layer 10, the
second axis of rotational symmetry, with respect to which the
crystal orientation of the crystal structure of potassium-sodium
niobate has fourfold symmetry and which is inclined from the
thickness direction, can become present in addition to the
above-described first axis of rotational symmetry in the
above-described thickness direction by performing the formation in
the first step at a temperature lower than the temperature in the
second step and the piezoelectric characteristics can be further
enhanced. The piezoelectric layer 10 may be formed in further more
steps.
[0050] In the above-described method for forming the piezoelectric
layer 10 in the two steps, the formation in the first step is
performed within the range of preferably 200.degree. C. to
500.degree. C. Meanwhile, the formation in the first step is
performed within the film thickness range of preferably 10 nm to
100 nm. There is a tendency that the piezoelectric characteristics
of the piezoelectric element can be further enhanced by performing
the first step within these temperature range and film thickness
range.
[0051] The piezoelectric element 100 according to the present
invention can contain at least one type of element selected from
the group consisting of Li (lithium), Ba (barium), Sr (strontium),
Ta (tantalum), Zr (zirconium), and Mn (manganese) in the
piezoelectric layer 10. Consequently, there is a tendency that the
piezoelectric characteristics of the element can be further
enhanced.
[0052] The second electrode layer 12 is made from, for example, Pt.
The second electrode layer 12 has a thickness of, for example, 0.02
.mu.m or more and 1.0 .mu.m or less. Alternatively, a metal
material, e.g., Pd, Rh, Au, Ru, Ir, Mo, Ti, or Ta or an
electrically conductive metal oxide, e.g., SrRO.sub.3 or
LaNiO.sub.3, can also be used as the second electrode layer 12. The
second electrode layer 12 can be formed by the sputtering method,
the vacuum evaporation method, the printing method, the spin
coating method, the sol-gel method, or the like.
[0053] In this regard, the substrate 4 may be removed from the
piezoelectric element 100. Consequently, the displacement and the
sensitivity of the piezoelectric element can be increased.
[0054] Also, the piezoelectric element 100 may be coated with a
protective layer. Consequently, the reliability can be
enhanced.
[0055] In the piezoelectric element 100, an intermediate layer may
be provided in any one of or both of between the first electrode
layer 8 and the piezoelectric layer 10 and between the
piezoelectric layer 10 and the second electrode layer 12.
[0056] As for this intermediate layer, an electrically conductive
oxide is used. In particular, SrRuO.sub.3, SrTiO.sub.3,
LaNiO.sub.3, CaRuO.sub.3, BaRuO.sub.3,
(La.sub.xSr.sub.1-x)CoO.sub.3, YBa.sub.2Cu.sub.3O.sub.7,
La.sub.4BaCu.sub.5O.sub.13, and the like are preferable because the
electrical conductivity is high and the heat resistance is
provided.
[0057] (Piezoelectric Actuator)
[0058] FIG. 2A is a configuration diagram of a head assembly
mounted on a hard disk drive (hereafter may be referred to as HDD)
as an example of piezoelectric actuators including these
piezoelectric elements. As shown in this drawing, a head assembly
200 includes a base plate 9, a load beam 11, a flexure 17, first
and second piezoelectric elements 13 serving as driver elements,
and a slider 19 provided with a head element 19a, as main
constituents thereof.
[0059] In this regard, the load beam 11 includes a base end portion
11b fixed to the base plate 9 by beam welding or the like, first
and second plate spring portions 11c and 11d extending from this
base end portion 11b while tapering, an opening portion 11e
disposed between the first and second plate spring portions 11c and
11d, and a beam main portion 11f following the first and second
plate spring portions 11c and 11d and extending linearly while
tapering.
[0060] The first and second piezoelectric elements 13 are disposed
on a wiring flexible substrate 15 which is part of the flexure 17,
while keeping a predetermined distance from each other. The slider
19 is fixed to an end portion of the flexure 17 and is rotated in
accordance with expansion and contraction of the first and second
piezoelectric elements 13.
[0061] The first and second piezoelectric elements 13 are formed
from a first electrode layer, a second electrode layer, and a
piezoelectric layer sandwiched between the first and second
electrode layers. The electric power consumption can be reduced so
as to enhance the reliability and a large displacement can be
obtained by using the piezoelectric element exhibiting a large
displacement as the piezoelectric element used for the
piezoelectric actuator according to the present invention.
[0062] FIG. 2B is a configuration diagram of a piezoelectric
actuator of an ink-jet printer head, as another example of the
piezoelectric actuator including the above-described piezoelectric
element.
[0063] A piezoelectric actuator 300 is formed by stacking an
insulating layer 23, a lower electrode layer 24, a piezoelectric
layer 25, and an upper electrode layer 26 on a substrate 20.
[0064] In the case where a predetermined ejection signal is not
supplied and a voltage is not applied between the lower electrode
layer 24 and the upper electrode layer 26, deformation does not
occur in the piezoelectric layer 25. A pressure change does not
occur in a pressure chamber 21 provided with a piezoelectric
element supplied with no ejection signal, and an ink droplet is not
ejected from a nozzle 27 thereof.
[0065] On the other hand, in the case where a predetermined
ejection signal is supplied and a certain voltage is applied
between the lower electrode layer 24 and the upper electrode layer
26, deformation occurs in the piezoelectric layer 25. The
insulating film 23 is bent to a great extent in a pressure chamber
21 provided with the piezoelectric element supplied with an
ejection signal. Consequently, the pressure in the pressure chamber
21 increases instantaneously, and an ink droplet is ejected from
the nozzle 27.
[0066] Here, the electric power consumption can be reduced so as to
enhance the reliability and a large displacement can be obtained by
using the piezoelectric element exhibiting a large displacement as
the piezoelectric element used for the piezoelectric actuator
according to the present invention.
[0067] (Piezoelectric Sensor)
[0068] FIG. 3A is a configuration diagram (plan view) of a gyro
sensor as an example of a piezoelectric sensor including the
above-described piezoelectric element. FIG. 3B is a sectional view
of the section taken along a line A-A shown in FIG. 3A.
[0069] A gyro sensor 400 is a tuning fork vibrator type angular
velocity detecting element provided with a base portion 110 and two
arms 120 and 130 connected to one surface of the base portion 110.
This gyro sensor 400 is obtained by micromachining the
piezoelectric layer 30, the upper electrode layer 31, and the lower
electrode layer 32 constituting the above-described piezoelectric
element to correspond with the shape of the tuning fork vibrator.
The individual portions (base portion 110 and arms 120 and 130) are
integrally formed by the piezoelectric element.
[0070] Each of drive electrode layers 31a and 31b and detection
electrode layer 31d is disposed on a first principal surface of one
arm 120. Likewise, each of drive electrode layers 31a and 31b and
detection electrode layer 31c is disposed on a first principal
surface of the other arm 130. Each of these electrode layers 31a,
31b, 31c, and 31d is obtained by etching the upper electrode layer
31 into a predetermined electrode shape.
[0071] Meanwhile, the lower electrode layer 32 disposed all over
second principal surfaces (principal surface on the back side of
the first principal surface) of the base portion 110 and the arms
120 and 130 functions as a ground electrode of the gyro sensor
400.
[0072] Here, the longitudinal direction of each of the arms 120 and
130 is specified to be a Z direction, and a plane including the
principal surfaces of the two arms 120 and 130 is specified to be
an XZ plane, so that an XYZ rectangular coordinate system is
defined.
[0073] When a drive signal is supplied to the drive electrode
layers 31a and 31b, the two arms 120 and 130 are excited in an
in-plane vibration mode. The in-plane vibration mode refers to a
vibration mode in which the two arms 120 and 130 are excited in a
direction parallel to the principal surfaces of the two arms 120
and 130. For example, when one arm 120 is excited in a --X
direction at a velocity V1, the other arm 130 is excited in a +X
direction at a velocity V2.
[0074] In the case where rotation at an angular velocity w is added
to the gyro sensor 400 under this state while the axis of rotation
is specified to be the Z axis, the Coriolis force is applied to
each of the two arms 120 and 130 in a direction orthogonal to the
direction of the velocity, and excitation occurs in an out-of-plane
vibration mode. The out-of-plane vibration mode refers to a
vibration mode in which the two arms 120 and 130 are excited in a
direction orthogonal to the principal surfaces of the two arms 120
and 130. For example, when the Coriolis force F1 applied to one arm
120 is in a -Y direction, a Coriolis force F2 applied to the other
arm 130 is in a +Y direction.
[0075] The magnitudes of the Coriolis forces F1 and F2 are
proportionate to the angular velocity .omega. and, therefore, the
angular velocity .omega. can be determined by converting mechanical
strains of the arms 120 and 130 due to the Coriolis forces F1 and
F2 to electric signals (detection signals) by the piezoelectric
layer 30 and taking them from the detection electrode layers 31c
and 31d.
[0076] The electric power consumption can be reduced so that high
reliability and sufficient detection sensitivity can be obtained by
using the piezoelectric element exhibiting a large displacement as
the piezoelectric element used for the piezoelectric sensor
according to the present invention.
[0077] FIG. 3C is a configuration diagram of a pressure sensor as a
second example of the piezoelectric sensor including the
above-described piezoelectric element.
[0078] A pressure sensor 500 has a cavity 45 to respond to
application of a pressure and, in addition, is formed from a
support member 44 to support a piezoelectric element 40, a current
amplifier 46, and a voltage measuring instrument 47. The
piezoelectric element 40 includes a common electrode layer 41, a
piezoelectric layer 42, and an individual electrode layer 43, which
are stacked in that order on the support member 44. Here, when an
external force is applied, the piezoelectric element 40 is bent and
the voltage is detected by the voltage measuring instrument 47.
[0079] High withstand voltage and sufficient detection sensitivity
can be obtained by using the piezoelectric element exhibiting a
large displacement as the piezoelectric element used for the
piezoelectric sensor according to the present invention.
[0080] FIG. 3D is a configuration diagram of a pulse wave sensor as
a third example of the piezoelectric sensor including the
above-described piezoelectric element.
[0081] A pulse wave sensor 600 is configured to be equipped with a
transmitting piezoelectric element and a receiving piezoelectric
element on a substrate 51. Here, in the transmitting piezoelectric
element, electrode layers 54a and 55a are disposed on the two
surfaces of the transmitting piezoelectric layer 52 in the
thickness direction, and in the receiving piezoelectric element,
electrode layers 54b and 55b are also disposed on the two surfaces
of the receiving piezoelectric layer 53 in the thickness direction.
In addition, electrodes 56 and upper surface electrodes 57 are
disposed on the substrate 51, where the electrode layers 54a and
54b are electrically connected to the upper surface electrodes 57,
respectively, by wirings 58.
[0082] In order to detect pulses of a living body, initially, the
substrate back surface (surface not equipped with the piezoelectric
element) of the pulse wave sensor 600 is brought into contact with
the living body. Then, when pulses are detected, a specific drive
voltage signal is output to both the electrode layers 54a and 55a
of the transmitting piezoelectric element. The transmitting
piezoelectric element is excited in accordance with the drive
voltage signal input into both the electrode layers 54a and 55a, so
as to generate an ultrasonic wave and transmit the ultrasonic wave
into the living body. The ultrasonic wave transmitted into the
living body is reflected by a bloodstream and is received by the
receiving piezoelectric element. The receiving piezoelectric
element converts the received ultrasonic wave to a voltage signal
and outputs from both the electrode layers 54b and 55b.
[0083] The electric power consumption can be reduced and high
reliability and sufficient detection sensitivity can be obtained by
using the piezoelectric element exhibiting a large displacement as
the piezoelectric element used for the piezoelectric sensor
according to the present invention.
[0084] (Hard Disk Drive)
[0085] FIG. 4 is a configuration diagram of a hard disk drive
equipped with the head assembly shown in FIG. 2A.
[0086] A hard disk drive 700 is provided with a hard disk 61
serving as a recording medium and a head stack assembly 62 to
record the magnetic information thereto and regenerate in a housing
60. The hard disk 61 is rotated by a motor, although not shown in
the drawing.
[0087] In the head stack assembly 62, a plurality of assemblies
formed from an actuator arm 64 supported by a voice coil motor 63
in such a way as to rotate freely around a spindle and a head
assembly 65 connected to this actuator arm 64 are stacked in the
depth direction in the drawing. The head slider 19 is attached to
an end portion of the head assembly 65 in such a way as to opposite
to the hard disk 61 (refer to FIG. 2A).
[0088] As for the head assembly 65 (200), a form in which the head
element 19a (refer to FIG. 2A) is fluctuated in two steps is
adopted. Relatively large movements of the head element 19a are
controlled by whole drive of the head assembly 65 and the actuator
arm 64 on the basis of the voice coil motor 63, and fine movements
are controlled by drive of the head slider 19 by the end portion of
the head assembly 65.
[0089] The electric power consumption can be reduced and high
reliability and sufficient accessibility can be obtained by using
the piezoelectric element exhibiting a large displacement as the
piezoelectric element used for this head assembly 65.
[0090] (Ink Jet Printer Device)
[0091] FIG. 5 is a configuration diagram of an ink-jet printer
device equipped with the ink-jet printer head shown in FIG. 2B.
[0092] An ink-jet printer device 800 is configured to primarily
include an ink-jet printer head 70, a main body 71, a tray 72, and
a head drive mechanism 73. The piezoelectric actuator 300 is
included in the ink-jet printer head 70.
[0093] The ink-jet printer device 800 is provided with ink
cartridges of four colors of yellow, magenta, cyan, and black in
total and is configured to be able to perform full color printing.
In addition, this ink-jet printer device 800 is provided with a
dedicated controller board and the like in the inside, and the ink
ejection timing of the ink-jet printer head 70 and scanning of the
head drive mechanism 73 are controlled. Meanwhile, the main body 71
is provided with the tray 72 on the back and is provided with an
automatic sheet feeder (automatic continuous sheet feeding
mechanism) 76 in the inside, so as to automatically send recording
paper 75 and deliver the recording paper 75 from a front-mounted
delivery port 74.
[0094] The electric power consumption can be reduced and an ink-jet
printer device exhibiting high reliability and high safety can be
provided by using the piezoelectric element exhibiting a large
displacement as the piezoelectric element used for the
piezoelectric actuator of this ink-jet printer head 70.
[0095] For example, the piezoelectric element according to the
present invention can be used for applications, e.g., a gyro
sensor, a shock sensor, and a microphone, taking advantage of a
piezoelectric effect and applications, e.g., an actuator, an
ink-jet head, a speaker, a buzzer, and a resonator, taking
advantage of an inverse piezoelectric effect, and is particularly
suitable for applications taking advantage of the inverse
piezoelectric effect.
EXAMPLES
[0096] The present invention will be more specifically described
below with reference to the examples and the comparative examples.
However, the present invention is not limited to the following
examples.
Production of Piezoelectric Element
Example 1
[0097] In the example, a term "base member" refers to a member to
be provided with a film in each step.
[0098] A silicon wafer (substrate 4) which was provided with a
thermal oxidation film (SiO.sub.2: insulating layer 6) and which
had a diameter of 3 inches and a thickness of 400 .mu.m was placed
as a base member in a vacuum chamber of a RF sputtering apparatus,
evacuation was performed and, thereafter, a film of Pt was formed
as a first electrode layer 8. The base member temperature in film
formation was specified to be 400.degree. C. and the thickness of
the first electrode layer 8 was specified to be 200 nm.
[0099] After the first electrode 8 was formed, an out-of-plane XRD
(X-ray diffraction) measurement was performed to examine the
orientation property in a direction perpendicular to the plane and
an in-plane XRD measurement was performed to examine the
orientation property in the in-plane direction. Examples of other
methods for examining the orientation property in the in-plane
direction include a method in which a sample cut in the plane
(in-plane) direction with a TEM (transmission electron microscope)
is subjected to electron beam diffraction.
[0100] The out-of-plane XRD measurement is divided into a symmetric
reflection measurement (2.theta./.theta. measurement) in which a
lattice plane parallel to the sample surface is measured and an
asymmetric reflection measurement in which a lattice plane
obliquely intersecting the sample surface is measured. In the
present invention, the 2.theta./.theta. measurement was
performed.
[0101] The in-plane XRD measurement is a technique to allow the
incident x rays to graze the surface of the thin film sample and
measure diffraction from the lattice plane orthogonal to the
surface in the thin film. In the present example, an in-plane axis
was fixed to a plane obtained by the out-of-plane XRD measurement
performed in advance and a measurement called a twist measurement
was performed. The twist measurement is a technique to evaluate the
in-plane symmetric property of the substrate in a specific
plane.
[0102] The in-plane axis was fixed to the Pt (111) face obtained by
the out-of-plane XRD measurement and the twist measurement was
performed. As a result, a clear peak was not obtained and it was
ascertained that the Pt (111) face was in-plane asymmetry.
[0103] Subsequently, the base member was transferred to a chamber
of a RF sputtering apparatus equipped with a sputtering target,
evacuation was performed and, thereafter, the base member was
subjected to reverse sputtering. As for an atmosphere gas in the
reverse sputtering, 50 sccm of Ar (argon) was supplied to the
inside of a chamber, and an electric power of 500 W was put in
under a pressure of 1 Pa for 30 seconds to perform a treatment.
[0104] A (K.sub.0.5Na.sub.0.5)NbO.sub.3 thin film was formed as a
piezoelectric layer 10 on the base member following the reverse
sputtering. As for a sputtering target, a
(K.sub.0.5Na.sub.0.5)NbO.sub.3 sintered material was used. The base
member temperature in film formation was specified to be
600.degree. C. and the thickness of the piezoelectric layer 10 was
specified to be 2,000 nm.
[0105] After the piezoelectric layer 10 was formed, an out-of-plane
XRD measurement was performed to examine the orientation property
in a direction perpendicular to the plane and an in-plane XRD
measurement was performed to examine the orientation property in
the in-plane direction.
[0106] In the present example, piezoelectric layer 10 was further
subjected to a pole measurement. The pole figure obtained from the
pole measurement is a diagram indicating what orientation does a
certain crystal face have in the sample and is a diagram in which
distribution of an azimuth concerned (this is referred to as pole)
is plotted with respect to intensity in a polar stereographic
projection drawing. That is, the information on the manner of
orientation of the crystal face concerned relative to the sample
surface can be obtained by looking at the pole figure.
[0107] The in-plane axis was fixed to the KNN (001) face obtained
by the out-of-plane XRD measurement and the twist measurement was
performed. As a result, it was ascertained that the KNN (001) face
had in-plane fourfold symmetry because a clear peak appeared about
every 90.degree..
[0108] It was ascertained from the pole figure obtained by pole
measurement of the KNN (001) face that the axis of rotational
symmetry is not inclined relative to the thickness direction of the
piezoelectric film.
[0109] It was ascertained from the lattice constant of the
piezoelectric layer 10 obtained by the above-described out-of-plane
XRD measurement and in-plane XRD measurement that the piezoelectric
layer 10 was an orthorhombic crystal.
[0110] From the results of the above-described in-plane XRD
measurement, it is believed that in the piezoelectric layer 10 of
the present example, two types of crystal structures are present in
the plane while parallel c axes are displaced 90.degree. with
respect to each other.
[0111] Thereafter, the base member was transferred again to another
chamber of the RF sputtering apparatus, evacuation was performed
and, then, a film of Pt was formed as a second electrode layer 12.
The base member temperature in film formation was specified to be
200.degree. C. and the thickness of the second electrode layer 12
was specified to be 200 nm.
[0112] After the second electrode layer 12 was formed, a laminate
including the piezoelectric layer 10 was patterned by
photolithography and dry etching, wet etching, and the wafer was
subjected to cutting work, so as to obtain a piezoelectric element
100 having a movable part dimension of 5 mm.times.20 mm.
Comparative Example 1
[0113] In the piezoelectric element production step in Example 1,
reverse sputtering before film formation of the piezoelectric layer
10 was not performed. A piezoelectric element of Comparative
example 1 was produced, where other element configurations and the
production steps were the same as those in Example 1.
[0114] After the piezoelectric layer 10 was formed, the
out-of-plane XRD measurement was performed to examine the
orientation property in a direction perpendicular to the plane and
the in-plane XRD measurement was performed to examine the
orientation property in the in-plane direction.
[0115] The in-plane axis was fixed to the KNN (001) face obtained
by the out-of-plane XRD measurement and the twist measurement was
performed. As a result, a clear peak was not obtained and it was
ascertained that the KNN (001) face was in-plane asymmetry. FIG. 6
shows the result of the twist measurement.
[0116] It was ascertained from the pole figure obtained by the pole
measurement of the KNN (001) face that the axis of rotational
symmetry was not inclined relative to the thickness direction of
the piezoelectric film.
[0117] It was ascertained from the lattice constant of the
piezoelectric layer 10 obtained by the above-described out-of-plane
XRD measurement and in-plane XRD measurement that the piezoelectric
layer 10 was an orthorhombic crystal.
Example 2
[0118] The piezoelectric layer 10 film formation step following the
reverse sputtering in Example 1 was performed in two steps. The
base material temperature during film formation in the first step
was specified to be 450.degree. C. and the thickness was specified
to be 50 nm. Successively, the same chamber was employed, the base
material temperature in the second step was specified to be
600.degree. C., and the thickness was specified to be 1,950 nm. A
(K.sub.0.5Na.sub.0.5)NbO.sub.3 thin film having a thickness of
2,000 nm in total was formed as the piezoelectric layer 10 by the
above-described two-step film formation. A piezoelectric element of
Example 2 was produced as with Example 1 except the element
configuration and the production steps described above.
[0119] After the piezoelectric layer 10 was formed, the
out-of-plane XRD measurement was performed to examine the
orientation property in a direction perpendicular to the plane and
the in-plane XRD measurement was performed to examine the
orientation property in the in-plane direction.
[0120] The in-plane axis was fixed to the KNN (001) face obtained
by the out-of-plane XRD measurement and the twist measurement was
performed. As a result, it was ascertained that the KNN (001) face
had in-plane fourfold symmetry because a clear peak appeared about
every 90.degree..
[0121] It was ascertained from the pole figure obtained by the pole
measurement of the KNN (001) face that the axis of rotational
symmetry inclined relative to the thickness direction of the
piezoelectric film was present in addition to the axis of
rotational symmetry in the thickness direction of the piezoelectric
film.
[0122] It was ascertained from the lattice constant of the
piezoelectric layer 10 obtained by the above-described out-of-plane
XRD measurement and in-plane XRD measurement that an orthorhombic
crystal and a tetragonal crystal were present together in the
piezoelectric layer 10.
[0123] From the results of the above-described in-plane XRD
measurement, it is believed that in the piezoelectric layer 10 of
the present example as well, two types of crystal structures are
present in the plane while parallel c axes are displaced 90.degree.
with respect to each other.
Example 3
[0124] The piezoelectric layer 10 film formation step following the
reverse sputtering in Example 1 was performed in two steps. The
base material temperature during film formation in the first step
was specified to be 450.degree. C. and the thickness was specified
to be 50 nm. Successively, the same chamber was employed, and the
base member was subjected to reverse sputtering. As for an
atmosphere gas in the reverse sputtering, 50 sccm of Ar (argon) was
supplied to the inside of a chamber, and an electric power of 1,000
W was put in under a pressure of 1 Pa for 15 seconds to perform a
treatment. Thereafter, the film formation in the second step was
performed. The base material temperature during the film formation
in the second step was specified to be 600.degree. C. and the
thickness was specified to be 1,950 nm. A
(K.sub.0.5Na.sub.0.5)NbO.sub.3 thin film having a thickness of
2,000 nm in total was formed as the piezoelectric layer 10 by the
above-described two-step film formation sandwiching the reverse
sputtering. A piezoelectric element of Example 3 was produced as
with Example 1 except the element configuration and the production
steps described above.
[0125] After the piezoelectric layer 10 was formed, the
out-of-plane XRD measurement was performed to examine the
orientation property in a direction perpendicular to the plane and
the in-plane XRD measurement was performed to examine the
orientation property in the in-plane direction.
[0126] The in-plane axis was fixed to the KNN (001) face obtained
by the out-of-plane XRD measurement and the twist measurement was
performed. As a result, it was ascertained that the KNN (001) face
had in-plane fourfold symmetry because a clear peak appeared every
90.degree..
[0127] It was ascertained from the pole figure obtained by the pole
measurement of the KNN (001) face that the axis of rotational
symmetry inclined relative to the thickness direction of the
piezoelectric film was present in addition to the axis of
rotational symmetry in the thickness direction of the piezoelectric
film.
[0128] It was ascertained from the lattice constant of the
piezoelectric layer 10 obtained by the above-described out-of-plane
XRD measurement and in-plane XRD measurement that the piezoelectric
layer 10 was a tetragonal crystal.
[0129] From the results of the in-plane XRD measurement, it is
believed that in the piezoelectric layer 10 of the present example,
the a axis or the b axis of the tetragonal crystal is parallel to
the film thickness direction of the piezoelectric film and two
types of crystal structures are present in the plane while parallel
c axes are displaced 90.degree. with respect to each other.
Example 4
[0130] A silicon wafer (substrate 4) which was provided with a
thermal oxidation film (SiO.sub.2: insulating layer 6) and which
had a diameter of 3 inches and a thickness of 400 .mu.m was placed
as a base substrate in a vacuum chamber of an electron beam
evaporation apparatus, evacuation was performed and, thereafter, a
film of Pt was formed as a first electrode layer 8 by an electron
beam evaporation method. The base member temperature during film
formation was specified to be 800.degree. C. and the thickness of
the first electrode layer 8 was specified to be 200 nm. A
piezoelectric element of Example 4 was produced as with Example 4
except the element configuration and the production steps described
above.
[0131] After the first electrode layer 8 was formed, the
out-of-plane XRD measurement was performed to examine the
orientation property in a direction perpendicular to the plane and
the in-plane XRD measurement was performed to examine the
orientation property in the in-plane direction.
[0132] The in-plane axis was fixed to the Pt(200) face obtained by
the out-of-plane XRD measurement and the twist measurement was
performed. As a result, it was ascertained that the Pt(200) face
had in-plane fourfold symmetry because a clear peak appeared every
90.degree..
[0133] After the piezoelectric layer 10 was formed, the
out-of-plane XRD measurement was performed to examine the
orientation property in a direction perpendicular to the plane and
the in-plane XRD measurement was performed to examine the
orientation property in the in-plane direction.
[0134] The in-plane axis was fixed to the KNN (001) face obtained
by the out-of-plane XRD measurement and the twist measurement was
performed. As a result, it was ascertained that the KNN (001) face
had in-plane fourfold symmetry because a clear peak appeared every
90.degree.. FIG. 7 shows the result of the twist measurement.
[0135] It was ascertained from the pole figure obtained by the pole
measurement of the KNN (001) face that the axis of rotational
symmetry inclined relative to the thickness direction of the
piezoelectric film was present in addition to the axis of
rotational symmetry in the thickness direction of the piezoelectric
film.
[0136] It was ascertained from the lattice constant of the
piezoelectric layer 10 obtained by the above-described out-of-plane
XRD measurement and in-plane XRD measurement that the piezoelectric
layer 10 was a tetragonal crystal.
[0137] From the results of the in-plane XRD measurement, it is
believed that the piezoelectric layer 10 of the present example is
formed from a crystal structure in which the c axis of the
tetragonal crystal is parallel to the film thickness direction of
the piezoelectric film.
[0138] The element configuration, the production steps, and the
crystal system of the piezoelectric layer in each of the examples
and the comparative examples are shown in Table 1.
[0139] (Evaluation of Piezoelectric Element)
[0140] The displacement when a voltage was applied to each of
piezoelectric elements of Examples 1 to 4 and Comparative example 1
was measured by using a laser Doppler vibrograph (produced by
Graphtec Corporation). Table 1 shows the values of displacements
measured by applying a voltage of sinusoidal wave (.+-.20 V) with a
frequency of 1 kHz, where the first electrode layer was connected
to a positive electrode and the second electrode layer was
connected to a negative electrode.
[0141] It was ascertained that the displacement of the
piezoelectric element of each of Examples 1 to 4, which was a
piezoelectric element provided with a thin film of potassium-sodium
niobate, i.e. a perovskite type compound represented by a general
formula ABO.sub.3, as a piezoelectric layer, wherein the crystal
orientation of the crystal structure of potassium-sodium niobate in
the above-described piezoelectric layer had in-plane fourfold
symmetry as a whole piezoelectric layer, where a first axis of
rotational symmetry was the thickness direction of the
above-described piezoelectric layer, was larger than the
displacement of the piezoelectric element of Comparative example 1
not satisfying the above-described requirements.
[0142] It was ascertained that the displacement of the
piezoelectric element of each of Examples 2 to 4 having a second
axis of rotational symmetry, with respect to which the crystal
orientation of the crystal structure of potassium-sodium niobate
had fourfold symmetry and which was inclined from the
above-described thickness direction, in addition to the
above-described first axis of rotational symmetry and including a
potassium-sodium niobate thin film, which contains at least a
tetragonal crystal, as a piezoelectric layer was larger than the
displacements of the piezoelectric elements of Comparative example
1 and Example 1 not satisfying the above-described
requirements.
[0143] Furthermore, it was ascertained that the displacement of the
piezoelectric element of each of Examples 3 and 4 including a
potassium-sodium niobate thin film, which was a tetragonal crystal,
as a piezoelectric layer was larger than the displacements of the
piezoelectric elements of Comparative example 1 and Examples 1 and
2 not satisfying the above-described requirements.
[0144] It was ascertained that the displacement of the
piezoelectric element of Example 4, in which the Pt(200) face of
the first electrode layer 8 had in-plane fourfold symmetry with
respect to the axis in the thickness direction, was larger than the
displacements of the piezoelectric elements of Comparative example
1 and Examples 1 to 3 not satisfying the above-described
requirements.
[0145] In the above-described examples, the ratio of K to Na, which
were primary components of the A site, was specified to be 1, that
is, x in K.sub.1-xNa.sub.x was specified to be 0.5. However, the
effect of the present invention does not change in compositions in
which x is other than 0.5. Meanwhile, in the above-described
examples, an additive was not added. However, the effect of the
present invention does not change when Sr, Mn, Zr, Li, Ba, and Ta
are added.
[0146] The piezoelectric element according to the present invention
is provided with a piezoelectric layer having a predetermined
crystal structure. Therefore, the electric power consumption can be
reduced so as to enhance the reliability and a large displacement
can be obtained by using the piezoelectric element exhibiting a
large displacement as the piezoelectric layer of the piezoelectric
actuator.
[0147] The electric power consumption can be reduced and the high
reliability and sufficient detection sensitivity can be obtained by
using the piezoelectric element exhibiting a large displacement as
the piezoelectric layer of the piezoelectric sensor.
[0148] The electric power consumption can be reduced and high
reliability and sufficient accessibility can be obtained by using
the piezoelectric element exhibiting a large displacement as the
piezoelectric element used for the head assembly of the hard disk
drive.
[0149] In addition, the electric power consumption can be reduced
and an ink-jet printer device exhibiting high reliability and high
safety can be provided by using the piezoelectric element
exhibiting a large displacement as the piezoelectric element used
for the piezoelectric actuator of the ink-jet printer head.
TABLE-US-00001 TABLE 1 First electrode Piezoelectric layer film
Piezoelectric layer film layer formation first step formation
second step Insulating Pt film Reverse film thickness/ Reverse film
thickness/ Displace- layer/ formation sputtering film formation
sputtering before film formation ment substrate method before KNN
temperature second step temperature KNN crystal system (.mu.m)
Comparative SiO.sub.2/Si sputtering none 2000 nm/600.degree. C. --
-- orthorohmbic crystal 0.30 example 1 Example 1 SiO.sub.2/Si
sputtering 500 W/30 sec 2000 nm/600.degree. C. -- -- orthorohmbic
crystal 1.09 Example 2 SiO.sub.2/Si sputtering 500 W/30 sec 50
nm/450.degree. C. none 1950 nm/600.degree. C. orthorohmbic 1.40
crystal.cndot.tetragonal crystal Example 3 SiO.sub.2/Si sputtering
500 W/30 sec 50 nm/450.degree. C. 1000 W/15 sec 1950 nm/600.degree.
C. tetragonal crystal 1.90 Example 4 SiO.sub.2/Si evaporation 500
W/30 sec 50 nm/450.degree. C. 1000 W/15 sec 1950 nm/600.degree. C.
tetragonal crystal 2.53
* * * * *