MINIATURE PHASE-CORRECTED ANTENNAS FOR HIGH RESOLUTION FOCAL PLANE THz IMAGING ARRAYS
An array of backward diodes of a cathode layer adjacent to a first side of a non-uniform doping profile and an Antimonide-based tunnel barrier layer adjacent to a second side of the spacer layer have a monolithically integrated antenna bonded to each backward diode. The Antimonide-based tunnel barrier may be doped with, for example, a non-uniform delta doping profile. An imaging/detection device includes a 2D focal plane array of an array of backward diodes, wherein each backward diode is monolithically bonded to an antenna, which array is located at the back of an extended hemispherical lens, and wherein certain of the arrays are tilted for correcting optics aberrations. The antennas may be a bow-tie antenna, a planar log-periodic antenna, a double-slot with microstrip feed antenna, a spiral antenna, a helical antenna, a ring antenna, a dielectric rod antenna, or a double slot antenna with co-planar waveguide feed antenna.
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This application claims benefit of provisional application Ser. No. 61/181,809 filed on May 28, 2009 and entitled “Miniature Phase-Corrected Antennas for High Resolution Focal Plane THz Imaging Arrays”, the disclosure of which is expressly incorporated herein by reference.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCHNot applicable.
BACKGROUNDNon-ionizing and penetrative nature of terahertz (THz) radiation makes it promising for various detection methods in the commercial and defense industry [1-2]. Likewise, in the medical scene, particular bands in the THz frequency regime can be identified as markers of malignant tissues. Tuned to these marker frequencies, THz radiation recently has been proposed as an effective tool for cancer detection that will exhibit satisfactory resolution, substantial penetration depth, and non-harmful radiation properties in contrast to the x-ray technology. This is especially true and important for the case of breast cancer with recently identified marker frequencies of 500 and 800 GHz. According to 2006 American Cancer Society surveillance research, one out of eight women will have breast cancer in their lifetime with 96% of these cases being curable if early detected. Moreover, real-time viewing and identification of the excised tissues during medical operation is highly desired in order to decrease the biopsy time and number of follow up operations.
Medical images using THz radiation typically are generated through a mechanical raster scan of the object. However, long image acquisition times associated with such a raster scan constitute a major bottleneck. Therefore, rapid THz imaging systems based on large arrays of sensitive detectors recently have been considered within the commercial and scientific communities. In the work disclosed herein, a focal plane imaging array topology with low noise and highly sensitive heterojunction detector diodes is developed. Specifically, we consider two major needs associated with the resolution of the THz imaging arrays constructed on extended hemispherical lenses. These needs include:
- (1) Compact THz detector layout for tightly packed 2D focal plane imaging arrays. For example, Schottky diodes monolithically integrated within double slot antennas were previously employed in heterodyne THz detectors settings. Although these detectors are attractive in conjunction with the double slot antennas (because of their high Gaussian beam coupling efficiency and diffraction limited patterns [3]), the need for local oscillator signal and relatively large low-pass IF filter sections do not allow for tightly packed array development.
- (2) Large number of antenna/detector elements (or equivalently pixels) without resorting to expensive and bulky lenses. When an extended hemispherical lens is used to focus the image on the array elements, reflections at the lens/air boundary significantly reduce coupling efficiency of the pixels positioned away from the lens axis. Therefore, the number of detector elements is significantly limited by the lens diameter, and cannot support imaging for scan angles beyond ±20° [4].
To alleviate these issues, in this disclosure, we disclose and verify a dual slot antenna element integrated with a zero-biased Sb-heterostructure backward diode [5] for direct detection of THz radiation. In addition, we consider improved antenna layouts that can support tilted radiation patterns in order to increase the number of detectors without resorting to expensive and large silicon lenses.
A general discussion of HBD structures is set forth in U.S. Pat. No. 6,635,907. An improved version of such HBD is used in the present disclosure. In particular, the Sb-heterostructure backward diode of use in the present disclosure is an InAs/AlSb/GaSb backward diode having a p-type δ-doping plane with sheet concentration of 1×1012 cm−2 in the n-InAs cathode layer, as disclosed in the following references: N. Su, R. Rajavel, P. Deelman, J. N. Schulman, and P. Fay, “Sb-Heterostructure Millimeter-Wave Detectors With Reduced Capacitance and Noise Equivalent Power,” IEEE Electron Device Letters, vol. 29, no. 6, pp. 536-539, June 2008; Su, Zhang, Schulman, and Fay, “Temperature Dependence of High Frequency and Noise Performance of Sb-Heterostructure Millimeter-Wave Detectors,” IEEE Electron Device Letters, Vol. 28, No. 5, May 2007; Fay, Schulman, Thomas, III, Chow, Boegeman, and Holabird, “High-Performance Antimonide-Based Heterostruccture Backward Diodes for Millimeter-Wave Detection,” IEEE Electron Device Letters, Vol. 23, No. 10, October 2002; and WO/2010/06966 published Feb. 22, 2010 (corresponding to PCT/US09/45288 filed on May 27, 2009). The disclosures of all of these references are expressly incorporated herein by reference.
Such preferred backward diodes as referenced immediately above can be described as a “cathode layer adjacent to a first side of a non-uniform doping profile, and an Antimonide-based tunnel barrier layer adjacent to a second side of the spacer layer having monolithically integrated antennas bonded thereto”. The Antimonide-based tunnel barrier of such backward diodes may be doped. Such doping may be a non-uniform delta doping profile. This HBD, then, will be referred to herein as “a cathode layer adjacent to a first side of a non-uniform doping profile, and an Antimonide-based tunnel barrier layer adjacent to a second side of the spacer layer” for ease in discussion.
BRIEF SUMMARYAn array of backward diodes of a cathode layer adjacent to a first side of a non-uniform doping profile and an Antimonide-based tunnel barrier layer adjacent to a second side of the spacer layer have a monolithically integrated antenna bonded to each backward diode. The Antimonide-based tunnel barrier may be doped with, for example, a non-uniform delta doping profile. An imaging/detection device includes a 2D focal plane array of an array of backward diodes, wherein each backward diode is monolithically bonded to an antenna, which array is located at the back of an extended hemispherical lens, and wherein certain of the arrays are tilted for correcting optics aberrations. The antennas may be a bow-tie antenna, a planar log- periodic antenna, a double-slot with microstrip feed antenna, a spiral antenna, a helical antenna, a ring antenna, a dielectric rod antenna, or a double slot antenna with co-planar waveguide feed antenna.
For a fuller understanding of the nature and advantages of the present device, reference should be had to the following detailed description taken in connection with the accompanying drawings, in which:
These drawings will be described in further detail below.
DETAILED DESCRIPTION THz Imaging System OverviewThe received radiation is rectified by the zero-bias diode and converted to a DC voltage measured through a wire-bonded pigtail. A 0.1 mm×0.2 mm pad, 20, with 5 mm gap is formed adjacent to the antenna layout as depicted in
Improved Off-Axis Detection with Asymmetrically Fed Miniature Slot Antennas
The number of detectors, 34, used to form a focal plane-imaging array under the extended hemispherical silicon lens, 32, is limited by the internal reflections at the lens surface [4]. To illustrate this, let us consider the off-axis radiation properties of the dual slot antenna elements designed in the previous section. Since the slots are positioned symmetrically around the feed in the x and y directions, the antenna radiates a pencil beam into the silicon half-space along the positive z (θ=0°) axis, 36, with 10.9 dB directivity. From the ray optics illustration shown in
Although ray optics demonstrates that any off-axis detection is simply possible with an appropriate element location, antennas positioned further way from the lens axis experience significant power loss due to the reflections, 42, at the lens/air boundary. As shown in
To alleviate this fundamental limitation and increase the number of allowable array elements for the same frequency and lens size, the disclosure proposes to minimize internal reflection using antenna structures, 40, with radiating patterns tilted towards the optical axis, 44, as shown in
Solid lines, 50, in
However, beam tilting supported by asymmetrically fed double slot antennas turn out to be limited by 25°. In order to enable beam tilting beyond 25°, the detector must consist of multiple antennas as illustrated in
Double slot antenna configuration is quite flexible for designs that can achieve excellent performance within a focal plane array (FPA) as seen in
The slot spiral antenna features broadband operation while maintaining a very small footprint. It is compact in size; thus, can easily be incorporated into a densely packed FPA. It exhibits a rather uniform radiation pattern throughout the operating frequency band. In
In addition to a spiral design, broadband performance also can be achieved by different antenna topologies, such as the one shown in
The narrow bandwidth of the versatile double slot antenna can be improved by modifying the antenna slots as depicted in
The achievable beam tilts for the 500 GHz-1 THz bands are shown in
As demonstrated in the previous section, focal plane THz imaging arrays (positioned at the back surface of an extended hemispherical lens) can employ small and directive slot antenna configurations in order to deliver the best detection performance in terms of sensitivity, loss, and resolution. That is, the antenna size must not be larger than that set by the diffraction limit of the lens aperture (1.22 λf/D), while the pattern is directive and symmetric with respect to the lens axis. The size of the antenna element becomes even more critical at multiband applications to obtain the best possible resolution at the high frequency regime.
For our frequencies of interest (breast cancer detection) at 500 GHz and 800 GHz, this disclosure proposes the double folded slot antenna configuration shown in
Clearly, smaller slot antenna/detector topologies are highly beneficial for high-resolution focal plane THz imaging arrays that will employ multiband detection. In addition, enabling pattern tilting for these multiband antennas will result in higher resolution without resorting to large and bulky lenses, as was discussed in the above.
HBD Structures with Matched Antennas
A device structure (see
Prior work by others using custom-grown structures has demonstrated extremely low 1/f noise and an intrinsic sensitivity that exceeds the theoretical limits of thermionic devices (e.g., Schottky diodes, planar-doped barrier diodes). To date, these demonstrations have been limited to W-band and below (<110 GHz). This effort sees the aggressive scaling of deep-submicron devices for extending their frequency range into the THz regime. These nanoscale devices will be integrated with antennas to form broadband FPA arrays that operate in the 100 GHz through THz regime.
Work on the present disclosure has already demonstrated a scalable 6×11 FPA monolithically-integrated with matched antenna-diode structures.1 Several alternative THz antenna architectures shown in
After considering the several alternative THz antenna architectures shown in
The integrated antenna-diode is shown in
This monolithic integration of sensor element and antenna allows the designer to flexibly modify the antenna topology. This modification can be done according to well-developed antenna design and microwave matching and filter theory techniques, in order to achieve a perfect match to the complex diode impedance. This highly promising integration of antenna and radiofrequency (RF) engineering is already opening up new avenues to develop a high-efficiency coupling of incident radiation into high-speed non-linear detectors. For example, similar approaches are being pursued to improve sensor responsivity and speed in the infrared (IR) and optical bands (using nano-antennas).
SUMMARYDisclosed herein is a dual slot antenna with tunable main-beam direction integrated with zero bias Sb-heterostructure backward diode for direct detection of THz radiation. The compact layout and high responsivity of such detector elements make them suitable to design 2D focal plane THz imaging arrays. Further, the disclosure proposed and demonstrated that the number of detectors supported by a fixed size silicon lens can be significantly increased by tuning the main radiation beam of each pixel to illuminate the optical axis. This can simply be achieved by shifting feed locations and/or introducing small parasitic slots into the antenna geometry. In addition, the disclosure demonstrated that double folded slot antennas are promising candidates for dual band THz detection of breast cancer. Improving resolution and enabling multiband detection are current challenges in the THz imaging arrays and can be addressed with the development of smaller antenna/detector topologies, as outlined in this disclosure.
Besides healthcare use of the disclosed detector system, other likely uses include, for example,
1. Biomedical
-
- THz imaging and diagnostics
- Cancer detection: Breast, oral, skin, prostate, and cervical
- Dental imaging
- Skin assessment: Burn diagnostics and dermatology, cosmetic diagnostics and treatment
- Orthopedic imaging (of exposed bones)
- Ablation: cancer treatment, cosmetic surgery, cosmetic therapeutics
- Volatile organic compound detection and spectroscopy
- Identifying polymorphs and hydrides in drug compounds
- Counter detection of drugs and pharmaceutical
-
- Microchip inspection
- Corrosion identification
- Gaseous compound inspection and detection
- Pharmaceutical quality control
- Package inspection
- Wind blade inspection
- Jet-propulsion inspection
- Material integrity and structural analysis
- Fuel cell quality control and diagnostics
- Process monitoring
- Pollution monitoring
- Diagnostics of natural gas pipelines
- Detection of separation of laminated materials
- Systems for 3D inspection of fragile art products
- Molecular recognition and protein folding
-
- Checkpoint screening
- Concealed contraband detection
- Controlled substances detection
- Harmful compound identification
- Biometrics (gates, hand, walking behavior)
- Imaging through fog
- Evaluation of agricultural products (imaging of fresh frozen samples, moisture differences, etc.)
-
- Line of sight high-speed digital and analog communications, >10 Gbits
- Military applications for high speed
- Extensions of broadband fiber optics
- High magnetic field application
- Sub-mmW and mmW astronomy
- Atmospheric observations/monitoring (such as ozone depletion)
- Guidance and ID systems
- Counter riot protection
-
- Aircraft penetration of dust and fog for improved visibility.
Additional fields of use include, for example, RF/EO/Optics imaging systems, RF/EO/Optics phased arrays, mmW imaging, mmW communications mmW adaptive arrays, mmW smart antennas, and UV Communications/Radios.
- Aircraft penetration of dust and fog for improved visibility.
While the device and its use have been described with reference to various embodiments, those skilled in the art will understand that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope and essence of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiments disclosed, but that the disclosure will include all embodiments falling within the scope of the appended claims. In this application all units are in the metric system and all amounts and percentages are by weight, unless otherwise expressly indicated. Also, all citations referred herein are expressly incorporated herein by reference.
REFERENCES
- [1] S. M. Hanham, T. V. Bird, B. F. Johnston, R. A. Minasian, “Dielectric Rods for THz Antenna Arrays”, WARS 2008.
- [2] M. C. Kemp et al, “Security Applications of Terahertz Technology”, Proceedings of SPIE, vol. 5070, 2003.
- [3] G. P. Gauthier, W. Y. Ali-Ahmad, T. P. Budka, D. F. Filipovic, and G. M. Rebeiz, “A Uniplanar 90-GHz Schottky-Diode Milimeter-Wave Receiver,” IEEE Transactions on Microwave Theory and Techniques, vol. 43, no. 7, pp. 1669-1672, July 1995.
- [4] D. F. Filipovic, G. P. Gauthier, S. Raman, and G. M. Rebeiz, “Off-Axis Properties of Silicon and Quartz Dielectric Lens Antennas,” vol. 45, no. 5, pp. 760-766, May 1997.
- [5] N. Su, R. Rajavel, P. Deelman, J. N. Schulman, and P. Fay, “Sb-Heterostructure Millimeter-Wave Detectors With Reduced Capacitance and Noise Equivalent Power,” IEEE Electron Device Letters, vol. 29, no. 6, pp. 536-539, June 2008.
- [6] D. F. Filipovic, S. S. Gearheart, and G. M. Rebeiz, “Double-slot antennas on extended-hemispherical and elliptical silicon dielectric lenses,” IEEE Transactions on Microwave Theory and Techniques, vol. 41, pp. 1738-1749, October 1993.
Claims
1. An array of backward diodes of a cathode layer adjacent to a first side of a non-uniform doping profile and an Antimonide-based tunnel barrier layer adjacent to a second side of the spacer layer having a monolithically integrated antenna bonded to each said backward diode.
2. The array of backward diodes of claim 1, wherein said antennas are one or more of broadband or single band.
3. The array of backward diodes of claim 1, wherein a plurality of smaller arrays is cut out therefrom.
4. The array of backward diodes of claim 1, wherein the Antimonide-based tunnel barrier is doped.
5. The array of backward diodes of claim 1, wherein the non-uniform doping profile further comprises a delta doping profile.
6. The array of backward diodes of claim 1, wherein said antennas are one or more of a bow-tie antenna configuration, a planar log-periodic antenna configuration, a double-slot with microstrip feed antenna configuration, a spiral antenna configuration, a helical antenna configuration, a ring antenna configuration, a dielectric rod antenna configuration, or a double slot antenna with co-planar waveguide feed antenna configuration.
7. The array of backward diodes of claim 6, wherein said antennas comprise said double-slot with microstrip feed antenna configuration.
8. An imaging/detection device comprising:
- a 2D focal plane array of backward diodes of a cathode layer adjacent to a first side of a non-uniform doping profile and an Antimonide-based tunnel barrier layer adjacent to a second side of the spacer layer having monolithically integrated antenna bonded to each said backward diode, which array is located at the back of an extended hemispherical lens.
9. The imaging/detection device of claim 8, wherein certain of said arrays are tilted for correcting optics aberrations.
10. The array of backward diodes of claim 8, wherein said antennas are one or more of broadband or single band.
11. The array of backward diodes of claim 8, wherein the Antimonide-based tunnel barrier is doped.
12. The array of backward diodes of claim 8, wherein the non-uniform doping profile further comprises a delta doping profile.
13. The array of backward diodes of claim 8, wherein said antennas are one or more of a bow-tie antenna configuration, a planar log-periodic antenna configuration, a double-slot with microstrip feed antenna configuration, a spiral antenna configuration, a helical antenna configuration, a ring antenna configuration, a dielectric rod antenna configuration, or a double slot antenna with co-planar waveguide feed antenna configuration.
14. The array of backward diodes of claim 13, wherein said antennas comprise said double-slot with microstrip feed antenna configuration.
15. An imaging/detection device comprising:
- a 2D focal plane array of an array of backward diodes, wherein each backward diode is monolithically bonded to an antenna, which array is located at the back of an extended hemispherical lens, and wherein certain of said arrays are tilted for correcting optics aberrations.
16. The array of backward diodes of claim 15, wherein said antennas are one or more of broadband or single band.
17. The array of backward diodes of claim 15, wherein the Antimonide-based tunnel barrier is doped.
18. The array of backward diodes of claim 15, wherein the non-uniform doping profile further comprises a delta doping profile.
19. The array of backward diodes of claim 15, wherein said antennas are one or more of a bow-tie antenna configuration, a planar log-periodic antenna configuration, a double-slot with microstrip feed antenna configuration, a spiral antenna configuration, a helical antenna configuration, a ring antenna configuration, a dielectric rod antenna configuration, or a double slot antenna with co-planar waveguide feed antenna configuration.
20. The array of backward diodes of claim 19, wherein said antennas comprise said double-slot with microstrip feed antenna configuration.
Type: Application
Filed: May 28, 2010
Publication Date: Dec 2, 2010
Applicant: THE OHIO STATE UNIVERSITY (Columbus, OH)
Inventors: Kubilay Sertel (Hilliard, OH), H. Lee Mosbacker (Columbus, OH), Gokhan Mumcu (Tampa, FL), Phillip Smith (Northbrook, IL)
Application Number: 12/789,805
International Classification: G01J 5/20 (20060101); H01Q 1/00 (20060101);