Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01Q—ANTENNAS, i.e. RADIO AERIALS
  • H01Q9/00—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements
  • H01Q9/005—Electrically-short antennas having dimensions not more than twice the operating wavelength and consisting of conductive active radiating elements for radiating non-sinusoidal waves
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/49—Method of mechanical manufacture
  • Y10T29/49002—Electrical device making
  • Y10T29/49016—Antenna or wave energy "plumbing" making

Definitions

• THz Antenna Array System and Method of Making a THz Antenna Array
• the invention relates to a THz antenna array with a number of THz antennas, wherein a THz antenna has a photoconductive region and a first electrode and a second electrode, which are arranged spaced apart over a distance range which laterally over at least a part of the photoconductive region extends.
• the invention further relates to a method for producing a THz antenna array with a number of THz antennas, wherein a THz antenna has a photoconductive region and a first electrode and a second electrode, which are arranged spaced apart over a distance range, extending laterally over at least a portion of the photoconductive region.
• THz antennas can be formed and fabricated in a variety of ways, including such. can be used as a receiver and / or as a transmitter.
• a first fundamental form of a THz antenna provides a semi-large antenna single structure, which is designed in the range between microscopic structures (below 100 ⁇ m) and macroscopic millimeter structures (> 1 mm).
• Such a THz antenna is from Stone et.al. in the article "Electrical and Radiation Characteristics of Semiconductor Photoconductive Terahertz Emitters" in IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, Vol. 52, no. 10, October 2004.
• US 5,401,953 discloses an integrated submillimeter radiation generation device, the device comprising an array of N photoconductive switches biased by a common voltage source and having an optical path difference from a common optical pulse at a repetition rate
• BEST ⁇ TEGUNGSKOPIE provides different optical delay for each of the switches.
• the triggering of the N-switches takes place via a pulse traveling along the entire array of N-switches up to a single antenna, which radiates submillimeter radiation spherically in all directions as a point source.
• THz antenna arrays of the type mentioned in the beginning of a number of THz antennas or THz antenna structures have improved performance and modulability thereof as well as an improved directional characteristic.
• a THz antenna or THz antenna structure basically has two spaced apart electrodes with an intervening photoconductive material, i. As a rule, an area with semiconducting material in which optical charge carriers can be generated on.
• the individual THz antennas or THz antenna structures usually have microscopic dimensions.
• the problem here is the decoupling of the individual THz antennas as elements of the array in order to avoid destructive interference of the THz far field - usually, for. in finger structures, adjacent elements of the array, e.g. two fingers each with intervening photoconductive material, biased against opposite polarity. For this purpose, different possibilities of decoupling the individual elements of the array have hitherto been provided.
• the disadvantage here is that the production of such structures is comparatively complicated, since, inter alia, two additional material layers have to be deposited for the optical partitioning of suitable regions of the THz antenna array - this is at least an electrical insulation layer for the isolation of electrodes of adjacent THz Antennas and an opaque layer to be deposited thereon, which is usually designed as a metal layer.
• a cross-sectional view of such a THz antenna array is shown in FIG.
• the additional optically ablative layers mentioned there can in principle adversely affect the performance of the antenna arrangement. It has been shown that the dark current is comparatively high, since in the sealed-off regions of the THz antenna array in the reverse more than 50% of the total dark current is generated. This leads to a higher energy consumption of the THz antenna arrays in the case of a THz emitter or to a lower sensitivity in the case of a THz detector. In addition, the production of such an array has proven to be comparatively expensive.
• the invention begins, whose object is to provide a THz antenna array and a manufacturing method, which has improved properties, in particular simplified compared to the known arrays and manufacturing method.
• the object is achieved by the invention by means of the THz antenna array of the type mentioned above, wherein according to the invention a lateral region between adjacent THz antennas of the array is formed virtually non-photoconductive, i. A photoconductivity may or may not be present compared to a portion of a THz antenna or is negligibly small.
• a lateral area between adjacent THz antennas of the array is virtually free of photoconductive material.
• adjacent THz active elements of the array i. THz antennas or structures are per se isolated from each other in terms of photoconductivity - unlike conventional structures of the type described above, in which also areas between adjacent THz-active elements are photoconductive.
• the object is achieved by the invention with a manufacturing method of the type mentioned, in accordance with the invention a starting material is provided with a photoconductive region,
• the electrodes are patterned on the photoconductive area
• the resulting structure of the THz antenna array is lifted from the starting material and transferred to a substrate.
• the concept of the invention thus provides a direct decoupling of the THz-active elements of the array, ie the THz antennas or THz antenna structures, according to which a lateral area between adjacent T'Hz antennas of the array is formed virtually non-photoconductive.
• the invention has recognized that thereby an optical generation of photoconductive charge carriers in the lateral region between adjacent THz antennas of the array per se is impossible or negligible, so that in these areas per se no THz radiation can take place, the one to could contribute to destructive far-field interference.
• additional measures of antenna decoupling such as the location-dependent modulation of the optical excitation, whether by binary gratings, frequency mixing, or an optical isolation of the lateral areas between adjacent THz antennas, can advantageously be omitted.
• the invention provides that a part of the photoconductive region in the lateral region between adjacent THz antennas of the array is removed, in particular completely removed.
• a corresponding THz antenna array has, in particular, a photoconductive region which points to a limited lateral extent, which does not significantly beyond the lateral extent of the distance range or over the lateral extent of the distance range and the electrodes.
• the THz antenna arrays provided in accordance with the inventive concept and the corresponding production method use in an inventive manner the principle of the epitaxial lift-off method using comparatively thin photoconductive films.
• the elements of the array forming THz radiation emitting or detecting structures according to the concept of the invention can thus be particularly flexible and adapt with little effort and without additional components to a variety of optical systems with full-surface optical excitation. It has been shown that the emission power or detection sensitivity is optimized in comparison to previously known THz antenna arrays. It has been found that a THz antenna array according to the concept of the invention generally has a dark current reduced by at least 50%, which additionally increases the consumption or the sensitivity of a detector. In addition, the aforementioned disadvantages of the prior art are largely avoided. Should be in the context of special applications nevertheless an additional location-dependent modulation of the optical excitation be desired, the proposed concept offers the advantage of an increased tolerance range for adjusting an optical frequency mixing excitation or a binary grating. Additional optically isolating layers of material are generally not necessary. The production of the THz antenna array according to the concept of the invention can be implemented particularly effectively and inexpensively.
• a lateral region between adjacent THz antennas of the array may also be optically transparent and / or non-conductive.
• the electrical losses or dispersion effects can advantageously be largely avoided both in the THz frequency range and in the optical range.
• the lateral region between adjacent THz antenna arrays is formed by means of a substrate, in particular by means of a sapphire or quartz glass substrate.
• the substrate does not necessarily have to be optically transparent, for example, undoped silicon is also suitable, since it is comparatively low in absorption and / or dispersion in the THz range.
• the lateral area between adjacent THz antennas - in particular at a deposition height of the photoconductive area and / or the electrodes - is material-free, i. a lateral area between adjacent THz antennas of the array is virtually completely removed during the manufacturing process.
• a THz antenna array according to the concept, in particular measures of the cited developments of the invention are advantageously designed optimized for collective impulsive optical excitation in the photoconductive region, preferably - depending on the photoconductive material - at an energy above. half of 0.9 eV.
• the optical excitation is preferably carried out by means of a femtosecond laser pulse, in particular in a wavelength range between 650 nm to 1200 nm, preferably between 750 nm and 850 nm.
• a THz antenna by means of a metal-semiconductor-metal structure (MSM structure) formed in which the electrodes as a metal and the photoconductive region is formed as a semiconductor.
• MSM structure metal-semiconductor-metal structure
• the photoconductive region is particularly advantageously formed by means of LT-GaAs. The properties of the conductor carriers in the photoconductive region which are relevant for the THz radiation emission or detection are thereby advantageously adjustable.
• the photoconductive region has at least one photoconductive layer arranged below the electrodes, in particular a layer which extends over the lateral extent of the spacer region and of the electrodes.
• the photoconductive region has at least one photoconductive layer, optionally only between the electrodes, in particular a layer which optionally extends only over the lateral extent of the distance region.
• the photoconductive region is advantageously limited to a thickness of 10 ⁇ m, preferably 5 ⁇ m, preferably 2 ⁇ m, preferably 1 ⁇ m.
• the photoconductive region advantageously has a thickness of at least 0.5 ⁇ m.
• THz antennas which are formed by means of electrodes in the form of a finger structure.
• a finger of the finger structure may have a geometry that contributes to the formation of a THz resonator. So resonant peaks of certain THz frequency ranges can be achieved.
• the finger of the finger structure particularly advantageously has in its lateral extent a T-shaped geometry pointing away from the photoconductive region.
• At least a first number of THz antennas can be at different potential compared to a second number of THz antennas. This opens up an additional possibility of radiation modulation by potential control of the THz antennas.
• the invention also leads to a system comprising a number of THz antenna arrays of the type described above, in which at least a first number of THz antenna arrays have different potentials compared to a second number of THz Antenna array is located.
• THz antenna arrays can be found in the further subclaims and serve above all to increase the efficiency. This can be achieved alone or in combination of different measures in the array design and / or antenna design, the optical excitation improvement and a functionalization of the layers and / or surfaces of the THz antenna array and / or the THz antenna.
• a distance of THz antennas is chosen comparatively large, in particular at ⁇ / 2 .
• a microlens or microlens array can be provided for focusing and aligning the optical excitation.
• a functionalized array of high-permittivity nanoparticles can serve for field enhancement.
• advantageous developments of the invention can be found in the subclaims and specify in detail advantageous possibilities for realizing the above-described concept within the scope of the task as well as with regard to further advantages.
• metal layers can be deposited by means of evaporation within the framework of the electrode structuring and a lifting off of unnecessary electrodic areas can take place.
• the electrode structuring can also take place by means of chemical etching of non-required electrodic areas.
• the photoconductive region is limited to a lateral extent that does not significantly exceed the lateral extent of the spacer region or the lateral extent of the spacer region and the electrodes.
• the removal of the part of the photoconductive region takes place by means of chemical etching of a lateral region between adjacent THz antennas of the array.
• the lifting of the resulting structure of the THz antenna array from the starting material is advantageously carried out by means of chemical etching of a sacrificial region below the photoconductive region.
• Fig. 1 a THz antenna array in cross section, as in the aforementioned article by Dreysburg et.al. is described;
• FIG. 2 shows a first embodiment of a THz antenna array in cross section according to the concept of the invention
• FIG. 3 shows a second embodiment of a THz antenna array in cross section according to the concept of the invention
• FIGS. 2 and 3 shows a plan view of the embodiments according to FIGS. 2 and 3;
• Fig. 5 • a micrograph of structures for
• THz antenna arrays according to the concept of the invention before the epitaxial lift off of the semiconductor starting material
• FIG. 6 shows the structures of FIG. 5 as THz antenna arrays after transfer to an optically transparent substrate
• FIG. 7 shows a plan view of a further embodiment of a THz antenna array for the formation of
• Fig. 8 is a schematic illustration of the manufacturing process for a preferred embodiment
• Fig. 9 is a schematic illustration of the excitation and emission method for a preferred embodiment
• FIG. 11 shows the further preferred embodiment in a three-dimensional, semitransparent schematic representation
• FIG. 12 shows an exemplary embodiment of a functionalized surface of a THz antenna with nanoparticles as an AFM recording.
• Fig. 1 shows a schematic cross-sectional representation of a known THz emitter according to be processed by means of optical lithography on the surface of a semi-insulating GaAs wafer 12 to the above-mentioned products by 'Dreyhaupt et.al ..
• Two interlocking finger electrodes 11 The distances of the fingers of the finger electrode 11 are 5 microns.
• the metallization of a finger electrode 11 consists of 5 nm chromium and 200 nm gold.
• An opaque further metallization in the form of an optically transparent metal layer 14 made of chrome-gold covers every second finger electrode distance.
• This second metal layer 14 is isolated from the first metal layer of the finger electrode 11 by an insulating layer 13 in the form of a polyimide layer of about 2 ⁇ m or a silicon oxide layer of 560 nm thickness.
• the substrate in the form of the GaAs wafer 12 has a thickness of about 500 ⁇ m.
• the concept of the invention provides a THz antenna array 20, 30, 40 before, in which a lateral region between adjacent THz antennas is formed virtually non-photoconductive, ie A photoconductivity may or may not be present compared to a portion of a THz antenna or is negligibly small. This is achieved, as described with reference to FIGS. 1 to 8, in that a lateral area between adjacent THz antennas is free of photoconductive material.
• FIG. 2 shows a THz antenna array 20 in cross-section, with a number of THz antennas 29, wherein a THz antenna 29 has a photoconductive region 22 and a first electrode 21A and a second electrode 21B.
• the electrodes 21A, 21B are spaced apart by a spacing region 24 that extends laterally across at least a portion of the photoconductive region 22.
• the lateral region 25 between adjacent THz antennas 22 of the array 20 is not photoconductive.
• the present embodiment does not provide photoconductive material in region 25.
• the photoconductive region 22 is limited to a lateral extent that does not extend beyond the lateral Extending the distance range 24 and the electrodes 21A, 21B goes beyond.
• the photoconductive region is formed from LT GaAs, which has a charge carrier lifetime which is advantageously low for the THz emission. This is an additional advantage over the commonly used GaAs substrate as a photoconductive material, on the other hand, having a comparatively high carrier lifetime and relatively disadvantageous dispersion and attenuation properties to the LT GaAs.
• the thickness of the electrodes 21A, 21B is about 200 nm.
• the thickness of the photoconductive region is about 1,000 nm, which is well below commonly used photoconductive layers.
• the thickness of the substrate is in the range of 500 microns.
• the substrate is designed as an optically transparent non-conductive substrate in the form of a sapphire substrate 23. This has a particularly low dispersion and attenuation both in the THz and in the optical frequency range.
• FIG. 3 shows a further particularly preferred embodiment of a THz antenna array 30, again comprising a number of THz antennas 39, wherein a THz antenna 39 has a photoconductive region 32 and a first electrode 31A and a second electrode 31B are spaced apart over a spacing region 34 that extends laterally across at least a portion of the photoconductive region 32.
• the THz antennas 39 are deposited on an undoped silicon substrate 33. The thicknesses of the layers are similar to those in FIG. 2.
• the electrodes 31A, 31B are "buried".
• the photoconductive region 34 has another photoconductive Layer 32B.
• the photoconductive region also has a layer 32B arranged between the electrodes 31A, 31B, which extends in the present case only over the lateral extent of the spacer region 34.
• FIG. 4 shows the embodiments shown in cross section in FIGS. 2 and 3 in cross-section, wherein the same reference numerals are used correspondingly.
• the finger structure of the electrodes 21A, 21B, 31A, 31B is visible.
• Fig. 5 shows a microscopic photograph of a structure for a THz antenna array according to the embodiment shown in Fig. 2, i. the THZ antenna array prior to epitactically lifting off the starting material, with an associated scale.
• the starting material is provided as schematically shown in Fig. 8a.
• this is a GaAs substrate 51 with an epitaxially deposited heterostructure layer of 100 nm GaAs (not shown), 100 nm AlAs 52 as sacrificial layer and a layer 53 of LT GaAs in the range between 500 and 2000 nm.
• the electrode structuring in the form of a finger structure 54 shown in FIG. 8b can take place firstly by spin-coating a photoresist and subsequent lithography. Thereafter, a metal vapor deposition of the electrode material and then a lifting (lift-off) of the unneeded metal surface by dissolving the photoresist in acetone. In another procedure, first of all the metal vapor deposition can take place and then a spin-coating of the photoresist and the following lithography can be provided. This is followed by a wet-chemical etching of the unnecessary metal surfaces.
• a photoresist has additionally been spin-coated with the following Lithograph. Thereafter, as shown in Fig. 8c, the LT-GaAs lateral regions between adjacent THz antennas of the array have been wet-chemically or dry-chemically etched away.
• an epitaxial lift-off of the entire antenna array structure 52 shown in FIG. 5 takes place by wet-chemical etching of the AlAs sacrificial layer, for example in fluoric acid.
• the THz antenna array of Fig. 5 is shown after the transfer illustrated in Fig. 8e to an unspecified carrier substrate 55.
• This may be undoped silicon, which has comparatively little absorption and dispersion in the THz range or optionally also be an additionally optically transparent substrate such as sapphire or quartz glass.
• the final THz antenna array at the end of the manufacturing process is illustrated in Fig. 8f.
• FIGS. 5 and 6 are excerpts. Relatively high numbers of pieces are produced during production by processing a large number of antenna arrays on a GaAs output substrate 51 in parallel.
• FIG. 7 shows a further particularly preferred embodiment of a THz antenna array 40 according to the invention in a schematic plan view, similar to that in FIG. 4.
• the finger structure of the electrodes 41A, 41B is illustrated with the intermediate spacing region 44 extending extends laterally over at least a portion of the photoconductive region 42.
• the THz antennas 49 of the array 40 are applied to an undoped silicon substrate 43 in accordance with the production method explained with reference to FIGS. 5 and 6.
• the finger-like electrodes 41A, 41B of the finger structure have in their lateral extent a T-shaped geometry 46 facing away from the photoconductive region, which is used to form a THZ resonator. the square-like region 48 between the electrodes 41A, 41B - contributes.
• THz antenna arrays 20, 30, 40 can furthermore be improved by an employment of nanotechnology, photonics and microsystem methods with respect to an achievable THz output signal power of preferably at least an order of magnitude are, but the production costs are affected only slightly.
• FIG. 9 shows a schematic representation of the THz antenna arrays 20, 30, 40 described above-here a detail of a THz antenna 29, 39, 49, 49 ', 49 "thereof, in the case of a darkened optical excitation 51, in particular in the photoconductive region 22, 32, 42, which is already focused in accordance with the improvement between the first electrode 21A, 31A, 41A and the second electrode 21B, 31B, 41B and not to a brightly represented THz emission 53 through the THz transparent shown substrate down, that leads from the excitation side in the direction of radiation.
• This further-education concept of a focused optical excitation can be achieved on the excitation side of the THz antenna by an arrangement, not shown here, of a microlens.
• the directivity of a THz antenna array can be significantly improved.
• FIGS. 10 and 11 relate firstly to the device design and secondly to the optical excitation and thirdly to an increase in efficiency by functionalization of the semiconductor surface with the aid of metallic nanoparticles. In the present case, these are realized in a further preferred embodiment of a THz antenna array 50 and exploit in an improved manner the potential of the classical field theory for the antenna arrays.
• the directivity of the arrangement of the THz antenna array 50 can be significantly improved, whereby the optical losses are significantly reduced in the surrounding overall system.
• the directivity also depends on the electromagnetic coupling of the individual antennas 59, which can also be improved by advantageous measures such as refractive index adjustments or the like.
• the directivity factor may be increased up to an order of magnitude or beyond.
• the increase in the antenna distance D may also mean an increase in inactive intermediate areas, ie an enlargement of the spacing areas 24, 34, 44 as described in the preceding figures.
• the microlens array 55 on the excitation side above a THz antenna 59 in the THz antenna array 50 is illustrated in the embodiment of a microlens focusing illustrated in FIG and the microlens array 55 comprehensive component integrated.
• the microlens array 55 focuses the optical excitation 51 in the form of the optical excitation beam on the periodically arranged antennas 59 of the THz antenna array. In this way it is possible, as shown in FIG.
• a microlens array provided specifically for the THz antenna array 50 can be designed, which correspond to the required antenna spacing D.
• THz signal generation can, as in the present case in the context of a modification, for example, the semiconductor surface, in the form of a deposited layer, consisting of separate gold nanoparticles reach.
• Metallic as well as other materials with a high dielectric constant in the form of particles with diameters in the range of a few nanometers are used here in addition to an increase in the sensor surface and for influencing the field dynamics of the charge carriers generated by the optical excitation.
• the microlens array 55 can be integrated with the THz antenna array 50 to form a THz-emitting component.
• THz antennas as a finger structure is shown schematically in FIG. 11, and above this in extrapolation representation the nanoscale, functionalized surface 61.
• such a surface 61 can be achieved as a cost-effective process, for example in the context of a deposition of gold nanoparticles on a SiO 2 surface. Such an example is shown in FIG.
• FIG. 12 shows an AFM image which illustrates the significant separation of the Au particles, which is particularly suitable for the above-described efficiency-enhancing effects of a THz conversion in the case of an emitter, as described, for example, in FIG. 9 or FIG. 10 is shown.
• a THz antenna Array as described in FIG. 1 to FIG. 8.

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• 2006
  • 2006-03-29 DE DE102006014801A patent/DE102006014801A1/de not_active Withdrawn
• 2007
  • 2007-03-29 US US12/294,442 patent/US8581784B2/en not_active Expired - Fee Related
  • 2007-03-29 JP JP2009501952A patent/JP2009531841A/ja active Pending
  • 2007-03-29 EP EP07723734.5A patent/EP1999456B1/de not_active Not-in-force
  • 2007-03-29 WO PCT/EP2007/002790 patent/WO2007112925A1/de not_active Ceased

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