GB2083694A - Application of lithium tetraborate to electronic devices - Google Patents
Application of lithium tetraborate to electronic devices Download PDFInfo
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- GB2083694A GB2083694A GB8116328A GB8116328A GB2083694A GB 2083694 A GB2083694 A GB 2083694A GB 8116328 A GB8116328 A GB 8116328A GB 8116328 A GB8116328 A GB 8116328A GB 2083694 A GB2083694 A GB 2083694A
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- lithium tetraborate
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- PSHMSSXLYVAENJ-UHFFFAOYSA-N dilithium;[oxido(oxoboranyloxy)boranyl]oxy-oxoboranyloxyborinate Chemical compound [Li+].[Li+].O=BOB([O-])OB([O-])OB=O PSHMSSXLYVAENJ-UHFFFAOYSA-N 0.000 title claims abstract description 18
- 239000013078 crystal Substances 0.000 claims abstract description 16
- 239000011149 active material Substances 0.000 claims abstract description 12
- 238000010897 surface acoustic wave method Methods 0.000 claims description 50
- 230000001902 propagating effect Effects 0.000 claims description 20
- ZOXJGFHDIHLPTG-UHFFFAOYSA-N Boron Chemical compound [B] ZOXJGFHDIHLPTG-UHFFFAOYSA-N 0.000 abstract description 2
- WHXSMMKQMYFTQS-UHFFFAOYSA-N Lithium Chemical compound [Li] WHXSMMKQMYFTQS-UHFFFAOYSA-N 0.000 abstract description 2
- 229910052796 boron Inorganic materials 0.000 abstract description 2
- 150000001875 compounds Chemical class 0.000 abstract description 2
- 230000007812 deficiency Effects 0.000 abstract description 2
- 229910052744 lithium Inorganic materials 0.000 abstract description 2
- 239000000463 material Substances 0.000 description 41
- 239000000758 substrate Substances 0.000 description 20
- 229910011129 Li2B407 Inorganic materials 0.000 description 17
- 230000008878 coupling Effects 0.000 description 11
- 238000010168 coupling process Methods 0.000 description 11
- 238000005859 coupling reaction Methods 0.000 description 11
- 229910011131 Li2B4O7 Inorganic materials 0.000 description 5
- 238000000034 method Methods 0.000 description 5
- 229910003327 LiNbO3 Inorganic materials 0.000 description 4
- 238000001514 detection method Methods 0.000 description 4
- 230000003993 interaction Effects 0.000 description 4
- 239000010453 quartz Substances 0.000 description 4
- 239000004065 semiconductor Substances 0.000 description 4
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N silicon dioxide Inorganic materials O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 4
- 230000005684 electric field Effects 0.000 description 3
- NJPPVKZQTLUDBO-UHFFFAOYSA-N novaluron Chemical compound C1=C(Cl)C(OC(F)(F)C(OC(F)(F)F)F)=CC=C1NC(=O)NC(=O)C1=C(F)C=CC=C1F NJPPVKZQTLUDBO-UHFFFAOYSA-N 0.000 description 3
- 239000013077 target material Substances 0.000 description 3
- 229910013637 LiNbO2 Inorganic materials 0.000 description 2
- 239000002800 charge carrier Substances 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 229920002120 photoresistant polymer Polymers 0.000 description 2
- 239000000126 substance Substances 0.000 description 2
- 238000001931 thermography Methods 0.000 description 2
- WSMQKESQZFQMFW-UHFFFAOYSA-N 5-methyl-pyrazole-3-carboxylic acid Chemical compound CC1=CC(C(O)=O)=NN1 WSMQKESQZFQMFW-UHFFFAOYSA-N 0.000 description 1
- WOIHABYNKOEWFG-UHFFFAOYSA-N [Sr].[Ba] Chemical compound [Sr].[Ba] WOIHABYNKOEWFG-UHFFFAOYSA-N 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- 239000004411 aluminium Substances 0.000 description 1
- 230000002547 anomalous effect Effects 0.000 description 1
- 238000003491 array Methods 0.000 description 1
- 230000006835 compression Effects 0.000 description 1
- 238000007906 compression Methods 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- XKENYNILAAWPFQ-UHFFFAOYSA-N dioxido(oxo)germane;lead(2+) Chemical compound [Pb+2].[O-][Ge]([O-])=O XKENYNILAAWPFQ-UHFFFAOYSA-N 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 238000005530 etching Methods 0.000 description 1
- 238000003780 insertion Methods 0.000 description 1
- 230000037431 insertion Effects 0.000 description 1
- 238000010884 ion-beam technique Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000009659 non-destructive testing Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 238000000926 separation method Methods 0.000 description 1
- 239000007787 solid Substances 0.000 description 1
- 230000003068 static effect Effects 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
Classifications
-
- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/36—Devices for manipulating acoustic surface waves
-
- H—ELECTRICITY
- H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
- H10N30/00—Piezoelectric or electrostrictive devices
- H10N30/80—Constructional details
- H10N30/85—Piezoelectric or electrostrictive active materials
- H10N30/853—Ceramic compositions
- H10N30/8542—Alkali metal based oxides, e.g. lithium, sodium or potassium niobates
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Materials Engineering (AREA)
- Ceramic Engineering (AREA)
- Physics & Mathematics (AREA)
- Acoustics & Sound (AREA)
- Multimedia (AREA)
- Surface Acoustic Wave Elements And Circuit Networks Thereof (AREA)
Abstract
An electronic device, such as a piezoelectric (Surface Wave, Bulk Wave) or pyroelectric device, exploiting the polar nature of an active material in which the active material is lithium tetraborate or a closely related compound for example one which has a slight deficiency or excess of Lithium or Boron. Various crystal orientations suitable for different devices are specified.
Description
SPECIFICATION
Application of lithium tetraborate to electronic devices
The present invention relates to the application of lithium tetraborate to electronic devices and in particular to surface acoustic wave, bulk wave resonant surface skimming bulk wave and pyroelectric detection devices. It also relates to devices used for the generation and detection of bulk waves in solids and liquids and devices for generation and detection of static displacements. Such devices are defined for the purpose of this invention as Electronic devices exploiting the polar nature of a material.
A surface acoustic wave device is defined for the purpose of the present invention as an electronic device which uses a piezoelectrically generated Rayleigh wave. Such devices include, Band Pass Filters, Delay
Lines, Tapped Delay Lines, Reflective Array Pulse Compression Filters, Chirped transducer filters and
Parametric Devices including Convolvers.
A Bulk Wave or Piezoelectric device is defined for the purpose of the present invention as an electronic device employing waves propagating in the bulk of the crystal material. Such devices include Band Pass
Filters Transducers for non destructive testing, Sonar devices Hydrophones, and Bulk Wave piezoelectric delay lines.
A pyroelectric device is defined for the purpose of the present invention as a device which uses pyroelectrically generated charge for sensing changes in temperature. Such devices include Pyroelectric
Thermal Imagers in which the pyroelectric target is scanned by a beam of charged particles, Single and
Multi-element detector arrays for use in equipment such as intruder alarms.
A suitable material for piezoelectric surface acoustic wave, bulk wave resonant and bulk wave transducer devices should possess defined electromechanical coupling and temperature compensation properties.
It is an object of the present invention to provide surface acoustic wave and bulk wave devices with good electrical and mechanical properties by the choice of material.
The present invention provides an Electronic Device exploiting the polar nature of an active material in which the active material is lithium tetraborate. Lithium tetraborate is herein defined to also include closely related compounds which for example, contain slight deficiencies or excess of lithium or Boron e.g.
Li2+tj,B407 or Li2B4+,207 where 61 and 62 are small numbers.
Lithium Tetraborate possesses the point symmetry 4 mm. The Z axis is conventionally defined as being parallel to the 4-fold symmetry axis. The X axis is defined as being perpendicular to the Z axis and parallel to the crystalographic (100) direction. The Y axis is mutually perpendicular to the X and Z axes.
An X cut Z propagating crystal or one that is close to X cut and Z propagating is particularly suited to
Surface Acoustic Wave Devices, a Z cut crystal orientation is particularly suited to Bulk wave devices, an X cut Y propogating crystal is particularly suited to Surface Skimming Bulk Wave devices and an X cut crystal is particularly suited to pyroelectric devices.
The choice of the material is however not the only factor in determining the characteristics of a surface wave or bulk wave device. The identification and selection of the crystal cut is a determining factor in the property of the device. By the choice of an appropriate angle of cut the characteristics of the material can be made to suit the particular required device. Appropriate cuts for the lithium tetraborate will be described hereinafter for various devices.
Lithium tetraborate, Li2B407 has been found to be a material which shows anomalous elastic constant temperature behaviour (i.e. certain coefficients of the elastic stiffness tensor increase with increasing temperature) which has been demonstrated by measurement using ultrasonic pulse-echo and piezoelectric resonance techniques. This means that the material may possess crystal cuts for piezoelectric bulk wave and
SAW (surface acoustic wave) devices which show zero temperature coefficients of frequency. The piezoelectric coupling factors for the material are moderate (for a Z-plate K0.4) which means that the bulk-wave and SAW coupling factors will be larger than those in quartz.The combination of the presence of temperature-compensated cuts with good piezoelectric coupling gives the material several advantages over the two materials most commonly used for SAW and bulk-wave devices: LiNbO3 and a-quartz (the former possesses good electromechanical coupling but shows no temperature compensation, while the latter shows temperature compensation but possesses only poor electromechanical coupling factors). These advantages include the ability to make wider bandwidth devices, showing smaller insertion losses than similar devices on a-quartz, while maintaining good frequency temperature stability.
Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings in which:
Figures 1 to 5 show for various crystal cuts as specified in graphs A, B and C respectively the variations of surface acoustic wave (S.A.W.) velocity Vs: SAW coupling factor k2s (defined conventionally as k52=28Vwhere V is the change in velocity of the surface wave which occurs as it passes under a conducting plane on the substrate surface) and TD the first order temperature coefficient of SAW delay with the change in the substrate orientation and SAW propagation direction. Figure 2 also shows in graph D the variation in SAW power-flow angle.
Figure 6 is a stereogram showing the orientation of the substrate plane normal and the SAW propogation direction defined by angles a, 0 and ,0.
Figure 7 shows a graph of dielectric loss (tan a) for lithium tetraborate plotted against frequency which is relevant to the properties of the material for use as a pyroelectric detector and,
Figure 8 shows the mean measured variation in specific time delay with temperature for several SAW delay lines fabricated on x-cut, Z propogating Li2B407 substrates.
Initial measurements of the piezoelectric and elastic properties of Li2B407 have indicated its promise as a piezoelectric surface acoustic wave (SAW) substrate and bulk wave (BW) resonator material. Table 1 shows the values of the elastic constant, dielectric constant and piezoelectric coefficient tensor moduli at a temperature of 20 C. Also listed in this table are the first order temperature coefficients of these moduli and the estimated standard errors in the various quantities.
TABLE 1
The piezoelectric, elastic and dielectric constant tensor coefficients of Li2B407
Coefficient Value at Estimated Units First-Order Temperature
20 C Enor Coefficient (10-80C-1)
C11E 12.71 0.11 1010Nm-2 -51
C12E 0.6 0.20 ,, +1600
C12E 2.94 0.15 " #390 C33E 5.38 0.83 " -21
C44E 5.38 0.04 " -22
C66E 5.74 0.05 - -200
e15 0.278 0.005 Cm-2 -349
e31 0.10 0.04 D -2300
e33 0.77 0.04 " +385 E;;1 0.80 0.01 10-10Fm-1 -92
Es88 0.78 0.01 + +120 CjE's are elastic constant stiffness coefficients at constant electric field are are piezoelectric coefficients are are crystal permittivities at constant strain
As stated a principal use of the material will be for SAW applications. The properties suitable for such applications are illustrated in Figures 1 to 6 and Figure 8.
Figures 1 to 5 show the computed variations of SAW velocity (Vs), SAW coupling factor Ks2 and the first order temperature coefficient of SAW delay with the change in the substrate orientation and the SAW propogation direction. Also shown, where approptiate, is the variation in SAW power-flow angle . The first set of orientations of interest are those shown in Figure 1. It can be seen that the computed SAW velocity maximises at 3920 ms-1 for #=30 while Ks2 decreases from 0.8 x 10 # = oto a value of 0.04 x 10-2 for # = = 450 All the orientations in this series show TD > 49 x 1 060C1. The k25 values are higher for the series of orientations represented in Figure 2, being in all cases greater than 0.65x 10-2.The predicted TD values vary from 49 x 10-6oC-1for 0 = oto 63 x 1 O-60C-1 for 0 = 450 Non-zero power-flow angles are observed for all orientations in this set with 0 < 0 < 450. Figure 3 shows the variations in SAW properties which occurs for [110] propagating waves as the substrate plane normal is rotated # from [ 001 ] to [110]. The SAW velocity increases from 3693 ms-' for 8 = 0 to 4152 ms-' for 8 = 75 .
The Ks2 value, however, decreases from 0.65 x 10-2 # = 0 to 0.016 x 10-2 for # = 75 . The orientation with the most promising predicted properties appears in Figure 4 with 0 = 45 , corresponding to an X-cut,
Z-propagating device, this is predicted to possess V, = 3510 ms-', Ks2 = 0.82 x 10-2 and TD = +5 x 10-6 C-1 at 20 C. Theoretical examination of this orientation over a wider temperature range has revealed that its time delay for surface waves is a parabolic function of temperature. It is, therefore, temperature compensated.
SAW delay lines with 48 cm wavelength, an aperture of 2.4 us, 25 fingers per transducer and a transducer separation of 2.6 mm were deposited on selected substrate orientations of Li2B407. Substrates were polished with Siton priorto deposition. A standard "float-off" procedure was used in which a negative photoresist was spun onto the substrates, windows defined in it and an Aluminium (Al) layer evaporated through the windows onto the exposed substrate surface, surplus Al being removed with the photoresist on washing.
Table 2a gives a comparison between some predicted and observed propagation properties for SAW delay lines fabricated on selected substrate cuts of Li2B407. It can be seen that there is very good agreement between the observed and predicted properties for all substrates. As noted above, the X-cut, Z-propagating orientation is of particular interest as this is predicted to show a parabolic variation of SAW time delay with temperature. Figure 8 shows the mean measured variation in the specific time delay (LI/zo) where lo is the delay at the turn-overtemperature) from - 1 0'C to 50'C for several delay lines facricated on the X-cut, Y propagating orientation.Fitting the curves for the individual devices to an equation of the form: AT = K2(T-T0)2 Tc gave the following mean constants k2 and To k2 = 227 (+ 50) x 10-9oC~2TO = 12+ 50C The observed SAW velocity is very similar to that predicted (see Table 2a) while the observed value of k52 is about 50% larger than the predicted value. The SAW properties of this orientation of Li2B407 are compared in
Table 2b with those of several other conventional SAW substrate materials.It can be seen that the observed coupling factor of 1.2 x 10-2 compares very well with the k2s for Y-cut, Z-propagating LiTaO3 and [ 100 ] -cut, [ 011 ] propagating Bi12SiO20. The total variation in delay time from - 1 0'C to +40'C for X-cut, Z-propagating Li2B407 is + 85 ppm, this compares with + 2350 ppm in Y-cut, Z propagating LiNbO3 and + 850 ppm in Y-cut,
Z propagating LiTaO2 over the same temperature range. This degree of temperature compensation, combined with the SAW coupling factor of 1.2% makes X-cut, Z propagating Li2B407 ideal for use in moderately-broad bandwidth SAW filters requiring good thermal stability.
TABLE 2a
Predicted and observed saw properties of lithium tetraborate
Orientation Angles Device Orientation in Degrees Predicted SAW properties observed SAW properties # # α Vs ks TD 10-60C-1 Vs ks TD 10-60C-1
ms-1 ms-1 90 6.7 90 6.7 X-axis Cylinder 3800#20 0.008 46 3808 0.014 52
#0.001 #9 0 0 90 Z-cut, X-Propagating 3860#20 0.008 46 3873 0.009 52
#0.001 0 90 90 X-cut, Z-Propagating 3510#30 0.008 Parabolic 3510 0.012 Parabolic
0.001 #6 90 6.7 0 6.7 X-axis boule 3860#20 0.007 53 3860 0.014 46
#0.001 #30 0 0 45 Z-cut, [110] Propagating 3690#30 0.007 57 3710 0.011 76
#0.001 #30 TABLE 2b
A comparison of Li2B4O7 with other SAW substrates
Substrate Orientation Angles Vs Ks # TD at 19 C
Material in degrees Substrate
# # α ms-1 x10 (Deg.) 10-6oC-1
Quertz 90 47.23 0 3159.5 0.14 0 0 St-cut
LiNbO2 90 90 90 3491.1 4.86 0 +94 Y-cut,Z-propagating
LiTaO3 90 90 90 3254 1.15 0 +34 Y-cut,Z-propagating
Bi12SiO20 0 90 45 1660 1.4 0 +18 (100)-cut, [011] propagating
Li2B4O7 0 90 90 3510 1.2 0 +5 X-cut, Z-propagating It is shown from this table that Li2B407 has several advantages over many of the other materials commonly-used for SAW devices. Other advantages include the facts that the material possesses a low melting point (950 C; c.f.1253 C in LiNbO3 and 1650 C in LiTaO3) which facilitates its growth by Czochralski techniques, and that it is a non-ferroelectric piezoelectric, which removes any requirement to pole the material before use.
Specific devices for which the material is suitable include SAW delay lines filters and convolvers for use in radar, communications and domestic video equipment. It may also be used in acousto-optic devices exploiting the interactions between laser beams and a propagating surface wave and acousto-electric devices in which a semiconductor is placed in close proximity to the propagating SAW and the interactions between the electric field associated with the SAW and the charge carriers in the semiconductor are exploited.
Li2B407 also has a set of pyroelectric and dielectric properties which make it suitable for use as a pyroelectric infra-red detector/thermal imaging system target material. Table 3 lists the values of its pyroelectric coefficient (p(T)), dielectric constant (e) and dielectric loss (tan b) measured parallel to the polar axis at room temperature (20 C). Also listed on this table are the material's volume specific heat (c1) and resistivity parallel to the polar axis (p), again at 20 C.
TABLE 2b
A comparison of Li2B4O7 with other SAW substrates
Substrate Orientation Angles Vs Ks # TD at 19 C
Material in degrees Substrate
# # α ms-1 x10 (Deg.) 10-6oC-1
Quartz 90 47.23 0 3159.5 0.14 0 0 ST-cut
LiNbO2 90 90 90 3491.1 4.86 0 +94 Y-cut, Z-propagating
LiTaO3 90 90 90 3254 1.15 0 +34 Y-cut, z-propagating
Bi12SiO20 0 90 45 1660 1.4 0 +118 (100)-cut, [011] propagating
Li2B4O7 0 90 90 3510 1.2 0 +5 X-cut Z-propagating
For definition of α, #, # - see Figure 6.
Vs = surface wave velocity Ks = coupling factor (SAW) # = power flow angle TD = temperature coefficient delay It is shown from this table that Li2B407 has several advantages over many of the other materials commonly-used for SAW devices. Other advantages include the facts that the material possesses a low melting point (950 C; c.f.1253 C in LiNbO3 and 1650 C in LiTaO3) which facilitates its growth by Czochralski techniques, and that it is a non-ferroelectric piezoelectric, which removes any requirement to pole the material before use.
Specific devices for which the material is suitable include SAW delay lines filters and convolvers for use in radar, communications and domestic video equipment. It may also be used in acousto-optic devices exploiting the interactions between laser beams and a propagating surface wave and acousto-electric devices in which a semiconductor is placed in close proximity to the propagating SAW and the interactions between the electric field associated with the SAW and the charge carriers in the semiconductor are exploited.
Li2B407 also has a set of pyroelectric and dielectric properties which make it suitable for use as a pyroelectric infra-red detector/thermal imaging system target material. Table 3 lists the values of its pyroelectric coefficient (p(T)), dielectric constant (E) and dielectric loss (tan b) measured parallel to the polar axis at room temperature (20 C). Also listed on this table are the material's volume specific heat (cl) and resistivity parallel to the polar axis (p), again at 20 C.
TABLE 3
The pyroelectric properties of a number of materials at 20 C
Material p(T) # tan # p c' F1=#### F2=########## p##o Tc
10-8 at 1592 Hz #cm Jcm-3k-1 10-10 10-8 sec. C
Ccm-2k-1 CcmJ-1
DTGS 3.3 25 2x10-3 > 1012 2.5 5.3 9.3 > 20 60
LiTaO3 1.9 43 1x10-3 > 1014 3.2 1.38 5.1 > 500 618
Sr0.5Ba0.5Nb2O6 6.5 380 3x10-2 1013 2.1 0.81 4.2 3.36 121
Pb5Ge3O11 1.1 45 1x10-3 5x1011 2.0 1.22 3.7 1.99 178
Li2B4O7 0.5 10 0.03 5x1010 3.2 1.6 0.5 0.04 - A substance's suitability for use in pyroelectric detection systems can be measured in terms of one of its pyroelectric figures -of-merit, which can be defined as follows. The voltage responsivity of a single element detector can be shown to be proportional to:
(This figure of merit also measures a material's suitability for use as a pyroelectric vidicon target material).
If the noise-sources in a single-element detector are considered, it can be shown that the Johnson Noise is minimised relative to the background temperature noise by chosing a material with the largest possible value of:
This figure measures material's suitability for use in a single element detector.
Finally, if a pyroelectric material is to be used as vidicon target it can be used in a conduction pedestal mode only if its electrical time constant, Tc = p. E.E.O is between 0.04 and 1 sec.
Table 3 lists the values of F1, F2 and p. E.E.O for Li2B407 and, for comparison, also lists the corresponding values for four other pyroelectric single crystals: lithium tantalate (LiTaO3), strontium barium niobate (SBN-Sr05Ba0.5Nb206), lead germanate (Pb5Ge3O,1) and deuteratedtriglycinesulphate (DTGS). It can be seen that, of these materials, DTGS gives the highest values for F1 and F2, although its electrical resistivity renders it unsuitable for use in a conventional mode pedestalvidicon tube, so that when it is used as a vidicon target other, less convenient, pedestal generation techniques are necessary. Furthermore, DTGS is relatively difficult to use because of its water solubility, low ferroelectric Curie temperature (Tc) and chemical instability at elevated temperatures.Of the other, more robust, oxide single crystal materials (LiTaO3, SBN or
Pb5 Ge3O11), LiTaO3 is the one most commonly used for single element detectors because of its high values of F1 and F2. Until recently, this has also looked to be the most promising material for use as an oxide pyroelectric vidicon target, in spite of its high electrical resistivity, and high thermal conductivity which necessitate reticulation of the target (i.e. dividing the target into thermally isolated islands = 50 m across by ion-beam etching).
Li2B407 possesses properties which give it a value of F1 slightly greater than LiTaO3 coupled with an electrical time constant of only 0.04 sec., making it good for use as a pyroelectric vidicon target which could be used in conduction pedestal mode. The high dielectric loss of Li2B407 indicates that it is not particularly suitable for use as a single-element detector material at frequencies below 2 KHz. However, as shown in
Figure 7 its loss is strongly dependent upon frequency so that at frequencies above 50kHz where tan 6 = x 1 0-3, F2 = 1.6 x 10-2 and therefore at these frequencies, although F2 is still considerably smaller than the value for LiTaO3, the material may be of interest for single element detectors.
Li2B407 has one other major advantage over the other materials in table 3 in that it is non-ferroelectric.
Thus, it does not need to be poled, nor is there any risk of any accidental thermal excursions depoling it, as there is with other more conventional materials. Furthermore, because it possesses no ferroelectric domains, there can be no problems with thermally generated noise caused by domain-wall motion, as would appear to be one problem with LiTaO3.
Li2B4O7therefore is a suitable material for a number of pyroelectric detector applications.
Claims (7)
1. An electronic device exploiting the polar nature of an active material in which the active material is lithium tetraborate.
2. A device as claimed in claim 1 which is a Surface Acoustic Wave device in which the active material is
Lithium Tetraborate on X-cut, Z propagating or an orientation close to X-cut or Z propagating.
3. A device as claimed in claim 1 which is a Surface Acoustic Wave device in which the active material is
Lithium Tetraborate on any other orientation than X-cut or using any orientation other than Z propagating.
4. A device as claimed in claim 1 which is a Bulk Wave device in which the active material is Lithium
Tetraborate on a Z-cut crystal orientation.
5. A device as claimed in claim 1 which is a Bulk Wave Device in which the active material is Lithium
Tetraborate on a crystal orientation other than Z-cut.
6. A device as claimed in claim 1 which is a Surface Skimming Bulk Wave device in which the active material is Lithium Tetraborate on X-cut Y propagating crystal.
7. A device as claimed in claim 1 which is a pyroelectric device in which the active material is Lithium
Tetraborate on an X-cut crystal.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8116328A GB2083694B (en) | 1980-06-11 | 1981-05-28 | Application of lithium tetraborate to electronic devices |
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB8019062 | 1980-06-11 | ||
| GB8116328A GB2083694B (en) | 1980-06-11 | 1981-05-28 | Application of lithium tetraborate to electronic devices |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| GB2083694A true GB2083694A (en) | 1982-03-24 |
| GB2083694B GB2083694B (en) | 1984-07-25 |
Family
ID=26275808
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GB8116328A Expired GB2083694B (en) | 1980-06-11 | 1981-05-28 | Application of lithium tetraborate to electronic devices |
Country Status (1)
| Country | Link |
|---|---|
| GB (1) | GB2083694B (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4489250A (en) * | 1982-06-30 | 1984-12-18 | Tokyo Shibaura Denki Kabushiki Kaisha | Temperature compensated surface acoustic wave device |
| EP0248233A2 (en) * | 1986-06-02 | 1987-12-09 | Hitachi, Ltd. | Cathode mounting a high-frequency piezoelectric chip |
-
1981
- 1981-05-28 GB GB8116328A patent/GB2083694B/en not_active Expired
Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4489250A (en) * | 1982-06-30 | 1984-12-18 | Tokyo Shibaura Denki Kabushiki Kaisha | Temperature compensated surface acoustic wave device |
| EP0248233A2 (en) * | 1986-06-02 | 1987-12-09 | Hitachi, Ltd. | Cathode mounting a high-frequency piezoelectric chip |
| EP0248233A3 (en) * | 1986-06-02 | 1990-01-24 | Hitachi, Ltd. | Cathode mounting a high-frequency piezoelectric chip |
Also Published As
| Publication number | Publication date |
|---|---|
| GB2083694B (en) | 1984-07-25 |
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Effective date: 20010527 |