WO1994005046A2 - Structures autonomes en materiaux a base d'oxyde du type perovskite - Google Patents

Structures autonomes en materiaux a base d'oxyde du type perovskite Download PDF

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Publication number
WO1994005046A2
WO1994005046A2 PCT/US1993/007933 US9307933W WO9405046A2 WO 1994005046 A2 WO1994005046 A2 WO 1994005046A2 US 9307933 W US9307933 W US 9307933W WO 9405046 A2 WO9405046 A2 WO 9405046A2
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layer
region
supportive
substrate
stmcture
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PCT/US1993/007933
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English (en)
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WO1994005046A3 (fr
WO1994005046A9 (fr
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Luke P. Lee
Michael J. Burns
Kookrin Char
Guo-Chun Liang
John M. Rowell
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Conductus, Inc.
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Priority to JP6506586A priority Critical patent/JPH08500702A/ja
Priority to AU55837/94A priority patent/AU5583794A/en
Priority to EP94901150A priority patent/EP0656153A1/fr
Publication of WO1994005046A2 publication Critical patent/WO1994005046A2/fr
Publication of WO1994005046A9 publication Critical patent/WO1994005046A9/fr
Publication of WO1994005046A3 publication Critical patent/WO1994005046A3/fr

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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/20—Permanent superconducting devices
    • H10N60/203—Permanent superconducting devices comprising high-Tc ceramic materials
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N—ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10N60/00—Superconducting devices
    • H10N60/01—Manufacture or treatment
    • H10N60/0268—Manufacture or treatment of devices comprising copper oxide
    • H10N60/0661—Processes performed after copper oxide formation, e.g. patterning
    • 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
    • H10N30/01—Manufacture or treatment
    • H10N30/08—Shaping or machining of piezoelectric or electrostrictive bodies

Definitions

  • This invention relates to freestanding structures incorporating high-quality thin films of perovskite-like oxide materials.
  • it relates to electronic device structures utilizing unsupported regions of thin films of high-temperature superconductors and ferroelectric materials.
  • the new superconductors are ceramics. Where metals are malleable and are easily formed into wires and magnets, ceramics are brittle and fragile, tending to break when stressed. Metals usually melt at reasonable temperatures of a few hundred degrees Celsius, so they can be molded. Ceramics often decompose instead of melting, and must be fired at high temperatures in oxidizing atmospheres. While metals are robust, suffering only local modification when subjected to acids or high energy particles, ceramics may undergo wider ranging damage during chemical attack.
  • the three major families of high-temperature superconductors are the 1-2-3 compounds such as YBa2Cu3 ⁇ 7_ ⁇ , the thalium compounds such as TlBaCaCuO (several phases superconduct), and the bismuthates such as BaSrCaCuO (several phases superconduct).
  • the oxide superconductors have a complicated crystal structure based on a simpler structure, that of perovskite CaTi ⁇ 3, and the superconductors are often said to have a "layered perovskite" structure.
  • the crystal structure can be thought of as a bottom layer of perovskite, a middle layer, and a top layer of perovskite, where the layers are stacked in the c-direction.
  • a c-axis film will always present what appears to be a perovskite unit cell to its substrate and to any layer grown on top of it.
  • HTS high-temperature superconductor
  • the O 2 " and Ca 2+ ions form a close-packed cubic (face-centered cubic, FCC) structure which then has four octahedral interstices and eight tetrahedral interstices.
  • the O 2 " anions occupy the cube face centers, the Ca 2+ cations the cube corners, and the Ti + cations one-quarter of the octahedral interstices.
  • there are eight cube comers per unit cell each shared by eight cells, for a total of one "A-site" per unit cell.
  • Good perovskite ferroelectrics include BaTi ⁇ 3, PbTi ⁇ 3, NaNb ⁇ 3, KNb ⁇ 3, NaTa ⁇ 3, and substituted stmctures such as Pb(Zr,Ti)O3 (PZT), Pbo.9Lao.i(Zr,Ti)O3 (PLZT) and (Ba,Sr)Ti ⁇ 3 in which the A sites are occupied by mixtures of Pb + , Sr, 2+ , Ba 2+ , La 2+ , Ca 2+ , and Cd 2+ , and the B sites are occupied by mixtures Ti 4+ , Nb 4+ , Sn 4+ , Hf 4+ , Z ⁇ , Ce 4+ , Th 4+ , and Ta 4+ .
  • ferroelectric materials is based on the corundum (sapphire, AI2O3) structure and is called "ilmenite.”
  • the unit cell of comndum has the O 2 ⁇ arranged to form a hexagonal close-packed (HCP) structure, and Al 3+ ions fill in two-thirds of the octahedral interstices.
  • HCP hexagonal close-packed
  • FeTi ⁇ 3 the Fe 2+ ions fill one-third of the octahedral site and the Ti 4+ fill the other one-third of these sites.
  • Alternating layers of cations are either all Fe + or all Ti + .
  • Ferroelectrics having the ilmenite structure include LiNb ⁇ 3 and LiTa ⁇ 3; in these materials each layer has an ordered arrangement of Li 2+ and Nb 4+ or Ta 4+ ions.
  • the ilmenite structure is related to the perovskite structure in exactly the same way that th HCP structure is related to the FCC structure.
  • the arrangement of atoms in the close-packed plane of both of these stmctures is the same/that is, a hexagonal lattice in which each atom has six nearest neighbors. This arrangement has interstices bounded by three atoms, and has two interstitial sites for every atom. In both stmctures these layers are stacked so that each plane fit tightly into the one below, with each subsequent plane translated so that the atoms match up wit one of the interstitial sites in the structure below.
  • the layers are stacked A B-C, that is the atoms in the third layer lie over the interstices in the second layer that match up with interstices in the first layer.
  • HCP stacking is A-B-A, that is the atoms in the third layer lie over the interstices in the second layer that match up with atoms in the first layer.
  • phase transitions reduce th symmetry of the crystal and allow anisotropic properties to develop.
  • the most useful forms of these materials are generally the orthorhombic stmctures. In this crystal structure, the angles between all of the major axes are 90° (right angles) but all three axes have slightly different lengths. Similar phase transitions occur in the ilmenite stmctures.
  • ferroelectrics While these materials are not generally used to carry current, their properties, too, depend on crystal orientation and the structural stability problems are the same as for the superconducting perovskites.
  • grain boundaries of about 0° ( ⁇ 5°) or 90° (+5°) are not too detrimental to the properties of the films.
  • these films are referred to as “single crystal” films, although they are not, strictly speaking, a single grain.
  • they will be referred to in this description as “nearly single crystalline” which is defined as having a constant surface normal (vector perpendicular to the plane of the film) and having no high-angle (5° ⁇ 85°) grain boundaries.
  • the high-T c oxide, or cuprate, superconductors are most useful when made in thin film form. Films from 5 to 500 nm can be deposited on supportive substrates and processed so that the material becomes superconducting at temperatures as high as 120 K. These films can be patterned into devices and circuits using techniques modified from those use in semiconductor processing. The superconducting devices and circuits that result have far better performance than similar stmctures made with normal (non-superconducting) metals, and are more convenient to use than are superconducting stmctures made from older superconductors that require cooling with liquid helium. The necessity of the supportive substrate, however, is a serious drawback for many applications.
  • thin films of the perovskite and ilmenite ferroelectrics are more appropriate than bulk forms of these materials.
  • the films For integration into silicon devices and circuits it is desirable to have very little material, so the films must be of the highest possible quality.
  • Completely unsupported thin films are extremely fragile. Once the substrate has been entirely removed the film usually falls apart because it lacks cohesiveness across voids or grain boundaries. The fragility is inherent in some cases, while in others it is enhanced by the thinning process.
  • TEM transmission electron microscopy
  • bolometers are infrared radiation detectors.
  • thermally decouple the bolometer from the substrate In this way, the bolometer can heat up and cool down much more quickly than its support substrate, and thermal conduction between the substrate and the detector is reduced, reducing the background noise.
  • piezoelectricity is the production of an electric field in response to a mechanical stress.
  • Polarized ferroelectrics have very high coupling coefficients, that is, they translate a large fraction of the mechanical force into electric voltage.
  • the present invention is a superconducting structure which has a high-quality thin film of high-T c superconductor decoupled from its supportive substrate.
  • the superconducting layer is deposited on a supportive substrate which is well matched to the superconductor layer.
  • an intermediate sacrificial layer is deposited.
  • the superconductive layer is deposited over both the substrate and the sacrificial layer and is patterned. Then, the sacrificial layer is removed, leaving the superconductive film only partially supported by the substrate.
  • the films must be grown epitaxially.
  • epitaxy a film is deposited on a substrate whose atomic arrangement forms a template for the crystal stmcture of the film.
  • silicon on silicon the process is called homoepitaxy.
  • YBCO is deposited by heteroepitaxy. More detailed process conditions for epitaxial film growth are described throughout the literature. Several chemical compositions are known to attack cuprate superconductor materials.
  • Sapphire single crystal AI2O3
  • lanthanum aluminate single crystal LaA103
  • sapphire has a fairly large lattice constant mismatch as well as a thermal expansion coefficient mismatch with YBa2Cu3 ⁇ 7_ ⁇ , it has the lowest dielectric loss tangent known.
  • Lanthanum aluminate has higher dielectric loss, but is very well lattice-matched to oxide superconductors and films grown on it so far exhibit even lower microwave surface resistance than films grown on sapphire.
  • YBa2Cu3 ⁇ 7 . ⁇ materials which are appropriate for subsequent epitaxial growth of YBa2Cu3 ⁇ 7 . ⁇ are SrTi ⁇ 3, CaTi ⁇ 3, Ce ⁇ 2, MgO, and YSZ (yttria-stabilized zirconia or cubic zirconia, Z1O.Y2O3). These materials can be used as substrates and are often used as buffer layers to improve the epitaxy of YBCO, or as dielectrics to insulate two or more superconducting layers.
  • Silicon micromechanical technology is rapidly evolving and a number of innovative fabrication techniques have recently been developed for micromotors and other articulated microstructures. Silicon micromachining is based on depositing and etching structural and sacrificial films. After deposition of the films, the sacrificial material is etched away, leaving a completely assembled micromechanical stmcture. For the case of polysilicon films, considerable work has been done over the last several years to demonstrate specific applications of such microstructures. Similarly, several techniques for making membranes are known in other art areas. Pressure sensors have been made out of silicon membranes for many years. These achievements have been reviewed in a special section of Science, vol.
  • HTS high-temperature superconductor
  • oxide nanostructure technology requires techniques and epitaxial multilayer structures which are intrinsically different from conventional Si micromachining technology. This is because HTS microstructures need to be built from an entirely epitaxial technology, in which successive layers must be highly aligned in both the growth direction (out-of-plane orientation) and the plane of the substrate (in-plane orientation).
  • the oxide superconductors are very anisotropic, having an orthorhombic crystal stmcture, unlike silicon, which is a cubic crystal.
  • YBa2Cu3 ⁇ 7_ ⁇ (YBCO) air bridge technique described here can be extended to make YBCO membrane stmctures for detectors and micromachines. See D. B. Rutledge, D. P. Neikirk, and D. P. Kasilingham, "Integrated Circuit Antennas", Chapter 1 in Infrared and Millimeter Wave, Vol. 10, (Academic Press, New York, 1983). It can also be applied to micromachining for the fabrication of such nanostmctures as micromotors and manipulators.
  • a stmcture in which a thin film of oxide superconductor has been deposited over a patterned dielectric material on a supportive substrate under conditions which result in a high degree of epitaxy and in-plane alignment in the superconductive layer.
  • the dielectric material can be removed from selected areas, leaving air bridges: regions where the superconductor film is no longer in contact with the supportive substrate.
  • a stmcture in which a thin film of oxide ferroelectric has been deposited over a patterned dielectric material on a supportive substrate under conditions which result in a high degree of epitaxy and in-plane alignment in the ferroelectric layer.
  • the dielectric material can be removed from selected areas, leaving air bridges: regions where the ferroelectric film is no longer in contact with the supportive substrate.
  • Air bridges impart multiple advantages in performance and operating economy to superconducting and ferroelectric devices.
  • Air bridge bolometers detectors of infrared radiation, are more sensitive when they are not in contact with a large thermal mass like a supportive substrate which contributes to the background radiation detected by the device.
  • the reaction time of the sensor is significantly reduced since only the active region needs to detect the radiation and it is not necessary to allow the substrate to come to thermal equilibrium with the detector.
  • air bridge switches will have reduced switching times when compared to supported stmctures.
  • Ferroelectric acoustic sensors and transducers are also more sensitive and quicker to respond when isolated from a supportive substrate.
  • Another object of this invention is to provide electronic devices and circuits of high-temperature superconductors which exhibit higher performance than their entirely supported counterparts by virtue of the removal of the supportive substrate in regions of interest.
  • the superconducting properties must not be degraded by the processing sequence, otherwise any advantage gained from the removal of the supportive substrate would be lost.
  • Another object of this invention is to provide a method for fabricating freestanding stmctures from thin films of high-temperature superconductor and ferroelectric materials withou degrading their electronic properties.
  • the special chemical nature of these classes of compounds, the perovskites and ilmenites, must be taken into account when designing the process.
  • the process should be manufacturable, that is, it should be robust and reproducible in order to be suitable for volume production.
  • a further object of the instant invention is to provide a method of micromachining cuprate superconductor materials.
  • the area of nanotechnology is still in its infancy, but the usefulness of miniature motors, pumps, and other mechanical and electromechanical devices is undisputed.
  • the techniques described here are those which must be mastered to make these micromachines from high-temperature superconducting materials.
  • One of the advantages of silicon micromotor is their low power dissipation. A micromotor fabricated entirely from superconducting material needs even less power because it is essentially lossless. Low loss can translate into high speed, broadband operation, and ultra-fine precision.
  • this invention is directed to a freestanding thin film of high-temperature superconductor material.
  • This stmcture exhibits all of the desirable properties of a thin film of high-Tc superconductor, including a high transition temperature, a high critical current density, good in-plane alignment, and a lack of high-angle grain boundaries.
  • the stmcture contains regions in which the superconducting film is no longer in contact with the supportive substrate. This feature allows the superconductor to be studied without interference from the substrate material. It also allows the active region of a superconductive device or circuit to be thermally and electrically decoupled from the substrate.
  • ferroelectric materials and stmctures can be formed using the same method with only very minor adjustments. Also disclosed is a manufacturing method for these stmctures. This process can be used to fabricate not only single stmctures, but the arrays of devices and circuits described below.
  • Figure 1 is an artist's rendition of a scanning electron microscope (SEM) microphotograph of the YBCO air bridge.
  • Figure 2 is a schematic perspective view of a cantilevered beam structure as shown in Figure 1.
  • FIG 3 is a schematic illustration of the sequence of steps involved in the formation of the YBCO air bridge.
  • Figure 4 is a schematic perspective view of the bridge structure formed by the steps of
  • Figure 5 is a schematic perspective view of a cantilevered switch structure with a buffer layer.
  • Figure 6 is a schematic perspective view of a bridging crossover stmcture.
  • Figures 7a and 7b show schematically a bolometer array stmcture made by the inventive technique.
  • Figure 7a is a side view of part of the stmcture.
  • Figure 7b is a schematic perspective view of part of the stmcture.
  • Figure 8 is a schematic perspective view of an air bridge crossover patterned to allow contact to three individual layers.
  • Figure 9 is a schematic side view of a membrane formed on a sacrificial substrate.
  • Figures 10a and 10b show the resistance vs. temperature curves of the YBCO microbridge.
  • Figure 10a shows its R vs. T behavior before the HF wet etch of the SrTi ⁇ 3 sacrificial layer;
  • Figure 10b shows its R vs. T behavior after the HF wet etch of the SrTi ⁇ 3 sacrificial layer.
  • Figures 11a and 1 lb show the current vs. voltage curves of a YBCO microbridge at 77 K.
  • Figure 11a shows the I-N behavior of the stmcture before the HF wet etch of the SrTi ⁇ 3 sacrificial layer
  • Figure lib shows the I-V behavior of the stmcture after the HF wet etch of the SrTi ⁇ 3 sacrificial layer.
  • a YBCO air bridge 20 fabricated on a LaAl ⁇ 3 substrate 22 is shown in Figure 1.
  • This cantilevered stmcture is shown schematically in Figure 2.
  • This 10- ⁇ m-wide air bridge 20 was grown over a sacrificial dielectric layer 28 which was subsequently etched away.
  • the bridge 20 is robust enough to stand up to wafer cleaving to leave the freestanding YBCO line seen in the SEM picture.
  • each layer deposited is epitaxial to the remaining underlying layer unless explicitly stated otherwise.
  • Epitaxial deposition results in the "nearly single crystalline" films described above.
  • the substrates 22 are cleaned by ultrasonic agitation in acetone and blown dry by clean dry nitrogen gas.
  • epitaxial SrTi ⁇ 3 28 is deposited on a LaAl ⁇ 3 substrate 22 as a sacrificial dielectric layer. After deposition, the SrTi ⁇ 3 28 is patterned with conventional photolithographic techniques to form the region of YBCO to be freestanding or suspended.
  • YBCO or another oxide superconductor 24 is then deposited over the patterned dielectric 28.
  • This superconducting layer 24 is patterned using photolithography followed by dry etching to define the extent of the superconducting regions of the final device stmcture.
  • the sacrificial dielectric layer 28 is removed by wet etching to leave a gap 26.
  • Figure 4 shows a schematic view of this stmcture.
  • the gap 26 is instantaneously filled with etchant solution; during operation the gap 26 may be filled with air, a cryogen, or vacuum, but it remains unsupported by the substrate 22.
  • the "substrate" 22 onto which the sacrificial layer 28 is deposited may be a previously grown epitaxial stmcture 32, as shown in Figures 5 through 8. This would be desirable, for instance, when the substrate 22 of choice is sapphire. Because sapphire reacts chemically with YBCO and other high-T c superconductors, a buffer layer 32 must be deposited between the sapphire and any YBCO layer. Thus, in regions where the SrTi ⁇ 3 28 will not remain during YBCO deposition a buffer layer 32 must be present.
  • the buffer material may be added before the SrTi ⁇ 3 has been deposited, or after the SrTi ⁇ 3 has been patterned.
  • the sacrificial dielectric layer 28 can be deposited by any method that will yield an epitaxial layer with the desired crystallographic orientation and surface smoothness. We currently use laser ablation (also known as pulsed laser deposition or PLD), reactive sputtering (on-axis or off-axis), and metal-organic chemical vapor deposition (MOCVD) to deposit dielectric layers.
  • laser ablation also known as pulsed laser deposition or PLD
  • reactive sputtering on-axis or off-axis
  • MOCVD metal-organic chemical vapor deposition
  • a sacrificial layer 28 For use as a sacrificial layer 28, we deposit 300 to 400 nm of an appropriate oxide, e.g., SrTi ⁇ 3, CaTi ⁇ 3, or MgO.
  • an appropriate oxide e.g., SrTi ⁇ 3, CaTi ⁇ 3, or MgO.
  • the particular dielectric material chosen must provide a good template for epitaxial crystal growth of a high-temperature superconductor material and it must be soluble in at least one solvent or solution which attacks the superconductor material much more slowly that it attacks the dielectric material. With these two primary considerations in mind, the choice of a particular material for this layer may be governed by arguments of convenience, expense, or availability.
  • a positive photoresist such as AZ® 4620 available from Hoescht Celanese, although negative photoresist could be used as well.
  • the desired pattern is formed in the resist by exposure through an appropriate mask, an optional bake to set the resist, and development of the resist according to the instructions provided by the resist manufacturer.
  • the pattern is transferred to the sacrificial layer by argon ion (Ar + ) milling.
  • the surface of the SrTi ⁇ 3 28 regions remaining after this step is 300 to 400 nm above the surrounding bare substrate 22 regions, requiring the subsequently deposited YBCO 24 to traverse a 300 to 400 nm step.
  • the substrate 22 is again cleaned, and the sacrificial layer 28 deposited.
  • the same substrate choices are available, but for the sake of illustration, YSZ will be used in this case.
  • YBCO will be the sacrificial layer 28.
  • the YBCO is patterned and the ferroelectric, say, PZT, is deposited as bridge layer 24. This layer 24 is patterned as before into a useful pattern such as a memory device, a transducer, or an electro-optic element.
  • the etchant is chosen to have a much higher rate of dissolution of YBCO 28 than of ferroelectric 24.
  • Most acids attack YBCO much faster than they attack other oxides.
  • diluted HNO3 will remove the YBCO while leaving all of the other materials in the stmcture.
  • a good dilution ratio is 0.5% HNO3 (off the shelf, that is, prediluted) in H2O.
  • Other acids, such as HC1 can be substituted as long as they etch YBCO much faster than the other materials.
  • PrBa2Cu3 ⁇ 7- ⁇ is completely interchangeable with YBa2Cu3 ⁇ 7- ⁇ -
  • a variation of this process, shown in Figure 9, is to use a substrate 22 of sacrificial material.
  • the substrate 22 is cleaned and a buffer layer 32 (if desired) is deposited, followed by superconductor 24.
  • the back side of the substrate 36 is then patterned and etched away in selected regions to form a membrane of superconductor 24.
  • the superconducting properties of the YBCO were examined to identify any possible degradation from the above processing steps.
  • the samples were mounted on a temperature-controlled copper sample platform which was inserted into a liquid helium dewar above the liquid helium level.
  • the temperature of the copper sample platform was controlled by a commercial temperature controller to within 10 mK, the samples were open to the colder helium gas.
  • the center portion of the air bridges should be below the temperature of the copper sample holder and the sample substrate.
  • Figure 10a we show the resistance versus temperature curve for an air bridge before the sacrificial SrTi ⁇ 3 was removed.
  • the YBCO air bridge was ⁇ 300 nm thick, 10 ⁇ m wide and after the removal of the SrTi ⁇ 3 sacrificial layer the suspended portion was 50 ⁇ m long.
  • the figure show a transition at 87 K with a width of about 1 K.
  • Figure 10b we show the resistance versus temperature for the same sample as in Figure 10a after removal of the SrTi ⁇ 3 sacrificial layer. As can be seen from a comparison of Figures 10a and 10b, there was no appreciable degradation in the width of the superconducting transition by the SrTi ⁇ 3 removal process.
  • the YBCO was reduced 8 to 16 nm in thickness. Thus its cross-sectional area was reduced from 4 ⁇ m 2 to ⁇ 3.8 ⁇ m 2 . This reduction in cross- sectional area should have caused a reduction in critical current of ⁇ 0.25 milliamps, from 5 milliamps to -4.75 milliamps.
  • An examination of the air bridges using SEM ( Figure 1) did not show any obvious cracks or constrictions. The fact that the observed reduction in critical current was a factor of 8 larger (-2 milliamps) might indicate that the region which produced the before- etch depressed critical current was more sensitive to the etching process than the rest of the YBCO.
  • Figures 5 and 6 show air bridges used as crossovers.
  • the bridging superconducting or ferroelectric layer 24 contacts the support structure 22, 32 at only one edge while the other edge is suspended. This produces a cantilevered stmcture which may be useful as a switch or sensor.
  • the bridging superconducting or ferroelectric layer 24 contacts the support structure 22, 32 at both edges producing a true bridge.
  • both of these stmctures are useful as sensors and switches.
  • the bridging superconductor layer 24 is electrically isolated from supportecTsuperconductor layer 34. No current flows between the two layers and the switch is "open.”
  • When an external force is applied to bridging superconductor layer 24 it deflects toward supported superconductor layer_ 34, eventually approaching close enough to "close” the switch and allow current to flow from one layer to the other. Physical contact is not necessary since the electrons are able to tunnel across a very small air (or other non-superconducting) gap.
  • a ferroelectric sensor operates much the same way, except that depression of the cantilever does not cause a current to flow, rather a voltage is developed.
  • the force can be induced in a number of ways. If the lever or bridge 24 is depressed physically, the switch acts as a pressure sensor. A magnetic field will repel the superconducting lever or bridge 24 so that the switch will be sensitive to magnetic fields. For some applications, the magnetic field can be induced by a control line carrying electrical current in proximity to the switch.
  • Air is a very good insulator. In these air bridge configurations, the air gap 26 can take the place of a traditional dielectric or insulating material.
  • Figures 7a and 7b show an array stmcture 30 suitable for bolometer arrays.
  • This type of stmcture has many advantages for bolometer construction. Unlike typical bolometer fabrication techniques, this bolometer stmcture is monolithic. There is no need to thin an auxiliary stmcture and later attach it. Thus the technology of this invention is more convenient for manufacturing.
  • the freestanding structures have very low thermal capacity and very low thermal mass. The low thermal capacity, due to the very small volume that reacts to the incoming infrared signal, makes the bolometer more sensitive. The low thermal mass, since it is not coupled thermally to a large substrate, reduces the background signal significantly.
  • the ease of assembling several bolometers into an array makes imaging feasible. This array of detectors yields spatial as well as chemical information.
  • Another application that follows from the low thermal resistance of the air bridge stmcture is a microwave switch.
  • the switching time of a component must be very fast.
  • a very fast switch results when an air bridge 20 is thinned laterally to reduce its cross- sectional area between two regions of broader superconductor.
  • the air bridge material is forced to go normal, that is, to transform from the superconducting state to the non-superconducting state. This is accomplished by exceeding either the critical current, the critical magnetic field, or the critical temperature of the material in the air bridge. Due to the slower response time of the surrounding areas and to their greater cross-sectional area, only the air bridge undergoes this change of state.
  • a micromotor can be made using the above techniques to pattern a dielectric layer in addition to the superconductor layers.
  • the dielectric piece When the dielectric piece is allowed to move freely between two charged plates of a capacitor, it can be made to rotate by applying a changing voltage to the plates.
  • the motor can then be used as a sensor or an actuator, since any change in the dielectric's local environment will change the rotation speed or direction, and the motion of the motor itself can be used to move other parts- of a circuit.
  • this motion can be used to change the width of a gap between two parts of another capacitor in the system in order to change the capacitance and resonant frequency of the circuit.
  • the motion can also be used to produce (or detect) ultrasonic or acoustic waves in the motor's vicinity.
  • air bridges One practical advantage of air bridges is the reduction in physical and thermal mass that results from the elimination of dielectric layers. Because superconductors must be cooled to superconduct, thermal mass reduction is desirable. Smaller, lighter stmctures require less coolant than larger, heavier ones. This translates into less expensive cooling technology and extended time between coolant replenishing. In addition, many of the air bridge devices have particular utility in satellites and spacecraft where size and weight reductions are most welcome.

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  • Engineering & Computer Science (AREA)
  • Manufacturing & Machinery (AREA)
  • Chemical & Material Sciences (AREA)
  • Ceramic Engineering (AREA)
  • Superconductor Devices And Manufacturing Methods Thereof (AREA)
  • Crystals, And After-Treatments Of Crystals (AREA)

Abstract

L'invention concerne un pont d'air autonome YBa2Cu3O7-δ ou ferroélectrique. Cette structure est utile pour des détecteurs à membrane et peut être étendue à des applications dans lesquelles la présence d'un substrat peut dégrader les propriétés électroniques, thermiques et optiques du supraconducteurs ou de la structure ferroélectrique. Le pont d'air est produit par photolithographie classique, attaque à sec par faisceaux d'ions, et attaque sélective à l'acide. Dans le mode de réalisation préféré, on dépose une couche diélectrique sacrificielle entre un substrat de support et une couche de matériau supraconducteur. La couche diélectrique est ensuite soumise à une attaque dans des régions sélectionnées afin de former le pont d'air. On a obtenu une couverture étagée de couches de pont épitaxiales sans dégradation significative des propriétés supraconductrices des couches de YBa2Cu3O7-δ. On peut également utiliser du YBa2Cu3O7-δ comme couche sacrificielle lorsqu'un ferroélectrique tel que Pb(Zr,Ti)O3 est le matériau de pont d'air voulu.
PCT/US1993/007933 1992-08-24 1993-08-24 Structures autonomes en materiaux a base d'oxyde du type perovskite WO1994005046A2 (fr)

Priority Applications (3)

Application Number Priority Date Filing Date Title
JP6506586A JPH08500702A (ja) 1992-08-24 1993-08-24 ペロブスカイト系酸化材料の自立型構造
AU55837/94A AU5583794A (en) 1992-08-24 1993-08-24 Freestanding structures of perovskite-type oxide materials
EP94901150A EP0656153A1 (fr) 1992-08-24 1993-08-24 Structures autonomes en materiaux a base d'oxyde du type perovskite

Applications Claiming Priority (2)

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US93476292A 1992-08-24 1992-08-24
US07/934,762 1992-08-24

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WO1994005046A2 true WO1994005046A2 (fr) 1994-03-03
WO1994005046A9 WO1994005046A9 (fr) 1994-04-28
WO1994005046A3 WO1994005046A3 (fr) 1994-06-09

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Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2310951A (en) * 1996-03-06 1997-09-10 Marconi Gec Ltd Micromachined devices
FR2745956A1 (fr) * 1996-03-06 1997-09-12 Marconi Gec Ltd Procede de fabrication d'une structure de micropont(s) pour dispositif micro-usine, et produits ainsi obtenus
US7078695B2 (en) 2002-06-03 2006-07-18 Oxford Instruments Analytical Oy Superconducting antenna-coupled hot-spot microbolometer, methods for its manufacture and use, and a bolometric imaging arrangement
US7338549B2 (en) 2003-12-22 2008-03-04 The Boc Group, Inc. Oxygen sorbent compositions and methods of using same
US7347887B2 (en) 2003-12-22 2008-03-25 The Boc Group, Inc. Oxygen sorbent compositions and methods of using same
EP2107039A2 (fr) * 2008-04-02 2009-10-07 Consiglio Nazionale delle Ricerche - INFM Istituto Nazionale per la Fisica della Materia Dispositif microélectromécanique à film mince d'oxyde de métaux de transition et son procédé de fabrication
DE102008001005A1 (de) 2008-04-04 2009-10-22 Forschungszentrum Karlsruhe Gmbh Verfahren zur Herstellung eines Schichtverbundes mit epitaktisch gewachsenen Schichten aus einem magnetischen Formgedächtnis-Material und Schichtverbund mit epitaktischen Schichten aus einem magnetischen Formgedächtnis-Material sowie deren Verwendung

Families Citing this family (1)

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Publication number Priority date Publication date Assignee Title
KR102390936B1 (ko) * 2017-08-31 2022-04-26 구글 엘엘씨 양자 정보 처리 디바이스 형성

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WO1989007259A2 (fr) * 1988-01-27 1989-08-10 The Board Of Trustees Of The Leland Stanford Junio Microscope a action tunnel avec balayage integre
EP0457468A2 (fr) * 1990-05-14 1991-11-21 AT&T Corp. Assemblage électronique intégré comprenant une ligne de transmission
WO1992010729A1 (fr) * 1990-12-12 1992-06-25 Regents Of The University Of Minnesota Micro-dispositif de detection ou d'application d'une force et son procede de fabrication

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Publication number Priority date Publication date Assignee Title
WO1989007259A2 (fr) * 1988-01-27 1989-08-10 The Board Of Trustees Of The Leland Stanford Junio Microscope a action tunnel avec balayage integre
EP0457468A2 (fr) * 1990-05-14 1991-11-21 AT&T Corp. Assemblage électronique intégré comprenant une ligne de transmission
WO1992010729A1 (fr) * 1990-12-12 1992-06-25 Regents Of The University Of Minnesota Micro-dispositif de detection ou d'application d'une force et son procede de fabrication

Non-Patent Citations (2)

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Title
APPLIED PHYSICS LETTERS. vol. 61, no. 22 , 30 November 1992 , NEW YORK US pages 2706 - 2708 L.P. LEE ET AL. 'Free-standing microstructures of YBa2Cu3O7 :A high-temperature superconducting air bridge' *
See also references of EP0656153A1 *

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2310951A (en) * 1996-03-06 1997-09-10 Marconi Gec Ltd Micromachined devices
FR2745956A1 (fr) * 1996-03-06 1997-09-12 Marconi Gec Ltd Procede de fabrication d'une structure de micropont(s) pour dispositif micro-usine, et produits ainsi obtenus
US5942791A (en) * 1996-03-06 1999-08-24 Gec-Marconi Limited Micromachined devices having microbridge structure
GB2310951B (en) * 1996-03-06 2001-04-11 Marconi Gec Ltd Micromachined devices
US7078695B2 (en) 2002-06-03 2006-07-18 Oxford Instruments Analytical Oy Superconducting antenna-coupled hot-spot microbolometer, methods for its manufacture and use, and a bolometric imaging arrangement
US7338549B2 (en) 2003-12-22 2008-03-04 The Boc Group, Inc. Oxygen sorbent compositions and methods of using same
US7347887B2 (en) 2003-12-22 2008-03-25 The Boc Group, Inc. Oxygen sorbent compositions and methods of using same
EP2107039A2 (fr) * 2008-04-02 2009-10-07 Consiglio Nazionale delle Ricerche - INFM Istituto Nazionale per la Fisica della Materia Dispositif microélectromécanique à film mince d'oxyde de métaux de transition et son procédé de fabrication
EP2107039A3 (fr) * 2008-04-02 2013-08-28 Consiglio Nazionale delle Ricerche - INFM Istituto Nazionale per la Fisica della Materia Dispositif microélectromécanique à film mince d'oxyde de métaux de transition et son procédé de fabrication
DE102008001005A1 (de) 2008-04-04 2009-10-22 Forschungszentrum Karlsruhe Gmbh Verfahren zur Herstellung eines Schichtverbundes mit epitaktisch gewachsenen Schichten aus einem magnetischen Formgedächtnis-Material und Schichtverbund mit epitaktischen Schichten aus einem magnetischen Formgedächtnis-Material sowie deren Verwendung

Also Published As

Publication number Publication date
JPH08500702A (ja) 1996-01-23
WO1994005046A3 (fr) 1994-06-09
AU5583794A (en) 1994-03-15
EP0656153A1 (fr) 1995-06-07

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