Non-contact probe measurement test bed for millimeter wave and terahertz circuits, integrated devices/components, systems for spectroscopy using sub-wavelength-size-samples

A test fixture for characterizing a device-under-test (DUT) includes first and second planar antennas and a planar waveguide arranged to guide terahertz (THz) and/or millimeter wave (mmW) radiation between the first and second planar antennas. The planar waveguide is further configured to couple THz and/or mmW radiation guided between the first and second planar antennas with the DUT. A beam forming apparatus is arranged to transmit a probe THz and/or mmW radiation beam to the first planar antenna of the test fixture. An electronic analyzer is configured to wirelessly receive a THz and/or mmW signal emitted by the second planar antenna responsive to transmission of the probe THz and/or mmW radiation beam to the first planar antenna. The planar antennas may be asymmetrical beam-tilted slot antennas.

BACKGROUND

The following relates to the millimeter or submillimeter, or equivalently extremely high frequency (EHF) to terahertz (THz), device characterization arts, millimeter to submillimeter (EHF to THz) device spectroscopy arts, millimeter or submillimeter (EHF or THz) device probe arts, and the like.

The International Telecommunication Union (ITU) designates the frequency range 0.3 THz to 3 THz (where 1 THz=1012Hz) as terahertz radiation, terahertz waves, or tremendously high frequency radiation. The terahertz radiation range can alternatively be written as the wavelength range 1 mm to 0.1 mm (or 100 micron), and hence the terahertz radiation range is also called submillimeter radiation, and is in the 0.1 mm to 1 mm range. The frequency range 30-300 GHz frequency range (1-10 mm wavelength range) is known as the Extremely High Frequency (EHF) or millimeter band, sometimes abbreviated as the “mmW” band. Thus, mmW radiation is in the 1 mm to 10 mm range. Sensor, transceiver, spectroscopy and communications systems, and the like electronic and photonic systems for the THz and mmW bands are distinctly different in technology and science as compared to lower frequency bands of the electromagnetic spectrum. Much like the infrared and optical frequency bands are separately addressed due to the aforementioned technological and scientific differences, the mmW and THz bands are also distinct from the rest of the radio frequency spectrum.

Recent advances in novel THz devices that exploit ultrafast quantum mechanical transitions in semiconductor systems (such as tunneling, plasma waves and so forth) are enabling new sensors for the THz band. New devices, such as heterostructure backward diodes (HBDs), 2D electron gas (2DEG) field effect transistors (FETs), high electron mobility transistors (HEMTs), metal-insulator-insulator-metal (MIIM) junctions and quantum cascade structures can be produced with cutoff frequencies well beyond 1 THz. In order to minimize parasitics and enable ultrafast operation, these devices typically have dimensions in the micrometer to nanometer scale. Such high speed devices are typically characterized in the millimeter wave (mmW) regime by contact probes. However, for the sub-millimeter or THz bands such probes are not readily available. For example, focal plane array antennas feature very small details that do not allow direct probe contact for input impedance characterization. Alternatively, indirect impedance characterization methods have been developed in order to characterize THz antennas.

BRIEF DESCRIPTION

In some illustrative embodiments disclosed as illustrative examples herein, an apparatus for performing terahertz (THz) or millimeter wave (mmW) characterization of an associated device-under-test (DUT) is disclosed. The apparatus comprises: a test fixture including first and second planar antennas and a planar waveguide arranged to guide THz or mmW radiation between the first and second planar antennas and further configured to couple THz or mmW radiation guided between the first and second planar antennas with the associated DUT; a beam forming apparatus arranged to transmit a probe THz or mmW radiation beam to the first planar antenna of the test fixture; and an electronic analyzer configured to wirelessly receive a THz or mmW signal emitted by the second planar antenna responsive to transmission of the probe THz or mmW radiation beam to the first planar antenna.

In some illustrative embodiments disclosed as illustrative examples herein, an apparatus is disclosed for performing characterization of an associated device-under-test (DUT) fabricated as a component of a test fixture that further includes first and second planar antennas and a planar waveguide connecting the first and second planar antennas with the DUT. The apparatus comprises: a beam forming apparatus configured to wirelessly transmit a probe THz or mmW radiation beam to the first planar antenna of the test fixture; a signal receiver configured to wirelessly receive a THz or mmW signal emitted by the second planar antenna in response to receipt of the probe THz or mmW radiation beam at the first planar antenna; and an electronic analyzer in wired connection with the signal receiver and configured to perform at least one of vector network analysis and spectroscopic analysis of the THz or mmW signal wirelessly received by the signal receiver.

In some illustrative embodiments disclosed as illustrative examples herein, an apparatus comprises an integrated circuit including a THz or mmW device under test (DUT), first and second planar antennas, and a planar waveguide arranged to guide THz or mmW radiation between the first and second planar antennas and further configured to couple THz or mmW radiation guided between the first and second planar antennas with the THz or mmW DUT. The apparatus may further comprise an electronic analyzer wirelessly connected with the THz or mmW DUT by wireless contacts comprising the first and second planar antennas.

In some illustrative embodiments disclosed as illustrative examples herein, a method is disclosed for characterizing a device-under-test (DUT). The method comprises: providing a test fixture including first and second planar antennas connected via the terahertz DUT; wirelessly transmitting probe THz or mmW radiation to the first planar antenna of the test fixture; and wirelessly receiving a THz or mmW signal characterizing the DUT which is emitted by the second planar antenna of the test fixture responsive to the transmitting. In some embodiments the analyzing of the received terahertz signal uses a vector network analyzer (VNA). In some embodiments the analyzing comprises performing spectroscopic analysis on the received THz or mmW signal. The providing operation may comprise monolithically fabricating on a substrate wafer or chip the DUT, the first and second planar antennas, and a waveguide connecting the first planar antenna and the second planar antenna with the DUT.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Disclosed herein are test beds and testing techniques for device and circuit testing at THz and mmW frequencies without the need to make electrical contact to convey electromagnetic signals. In some embodiments, the disclosed non-contact probe design includes beam-tilted THz and/or mmW antennas integrated into the coplanar environment of monolithic circuits and devices, such as high-speed transistors, diodes and integrated circuits. In some illustrative embodiments, a commercially available THz and/or mmW vector network analyzer (VNA) (with extension modules) and waveguide-fed horn antennas are used to excite the beam-tilted planar THz and/or mmW antennas integrated into the test device feed lines. In some embodiments, an extended hemispherical lens configuration is used to enhance THz and/or mmW coupling efficiency. Propagation effects and the antenna coupling artifacts are optionally removed using a conventional calibration method using several known loads (for example, a standard and short circuit loads).

With reference toFIG. 1, an illustrative apparatus for performing THz and/or mmW characterization of a device-under-test (DUT)8is described. The DUT8may, by way of non-limiting illustrative example, comprise a heterostructure backward diode (HBD), a two-dimensional electron gas (2DEG) field effect transistor (FET), a high electron mobility transistor (HEMT), a metal-insulator-insulator-metal (MIIM) junction, a quantum cascade structure, an integrated circuit such as a low noise amplifier, a power amplifier, a THz and/or mmW mixer, a THz and/or mmW sensor, or so forth. Such devices can be produced with cutoff frequencies well beyond 1 THz. See, e.g. Rajavel et al., “Sb-Heterostructure millimeter-wave detectors with reduced capacitance and noise equivalent power,”IEEE Electron Device Letters, vol. 29, no. 6, June 2008; Dyakonov et al., “Plasma wave electronics: Novel Terahertz devices using two dimensional electron fluid,” IEEE Trans. Electron Devices, vol. 43, p. 1640-1645, October 1996; Knap et al., “Nonresonant detection of Terahertz radiation in field effect transistors”,J. Appl. Phys., vol. 91, pp. 9346-9353, 2002; Williams et al., “3.4-THz quantum cascade laser based on longitudinal-optical-phonon scattering for depopulation”,Appl. Phys. Lett., vol. 82, pp. 1015-1017, 2003. The DUT8is mounted on, or fabricated as part of, a test fixture10, which is a device or setup designed to hold the DUT8in place and allow it to be tested by being subjected to controlled electronic test signals. The illustrative test fixture10includes, a first planar antenna12, a second planar antenna14, and a planar waveguide16arranged to guide THz and/or mmW radiation between the first and second planar antennas12,14. The planar waveguide16is further configured to couple THz and/or mmW radiation guided between the first and second planar antennas12,14with the DUT8. A THz and/or mmW beam forming apparatus is arranged to transmit a probe THz and/or mmW radiation beam18to the first planar antenna12of the test fixture10. In the illustrative example ofFIG. 1, the THz beam forming apparatus includes a THz and/or mmW radiator, such as an illustrative horn antenna20(or alternatively a broadband, quasi-optical, photoconductive-switch-based THz and/or mmW radiator synchronized by a femto-second pulsed laser, or another THz and/or mmW radiator), and a lens22focusing THz and/or mmW radiation from the THz and/or mmW radiator20onto the first planar antenna12of the test fixture10to form the probe THz and/or mmW radiation beam18. In the illustrative example, the probe signal is generated by a THz and/or mmW frequency extension module24operatively connected with a THz and/or mmW vector network analyzer (VNA)26.

An electronic analyzer, such as the illustrative THz and/or mmW VNA26, or a spectrum analyzer, or a power detector (Golay cell or a THz pyroelectric sensor), or so forth, is configured to wirelessly receive a THz and/or mmW signal28emitted by the second planar antenna14responsive to transmission of the probe THz and/or mmW radiation beam18to the first planar antenna12. In the illustrative embodiment ofFIG. 1, a THz and/or mmW receiver30, such as an illustrative horn antenna, is operatively coupled with the electronic analyzer26, and a receiving lens32conveys the THz and/or mmW signal28emitted by the second planar antenna14to the THz and/or mmW receiver30. A second THz and/or mmW frequency extension module34is operatively connected with the THz and/or mmW VNA26to input the received THz and/or mmW signal to the VNA26.

In the illustrative example ofFIG. 1, the lenses22,32are constructed as a unitary lens40that defines the lens surface22configured to focus the probe THz and/or mmW radiation beam18onto the first planar antenna12, and that defines the lens surface32wirelessly coupling the THz and/or mmW signal28emitted by the second planar antenna14to the THz and/or mmW signal receiver30. In the illustrative embodiment the unitary lens40comprises a hemispherical lens defining the lens surfaces22,32and further having a planar back side44on which the test fixture10is disposed. The illustrative unitary lens40may also be referred to as an extended hemispherical lens as it includes a hemispherical portion and an extension portion meeting the hemispherical portion at a junction diagrammatically denoted by a dotted line46inFIG. 1. As seen inFIG. 1, in this illustrative embodiment the wireless path from the first lens surface22to the first planar antenna12is contained in the unitary lens40, and the wireless path from the second planar antenna14to the second lens surface32is also contained in the unitary lens40. In practice, the two lens surfaces22,32overlap significantly. This illustrative embodiment reduces signal losses at interfaces between different materials and enables efficient coupling of the wireless THz and/or mmW signals onto the planar antennas of the text fixture.

With continuing reference toFIG. 1and with further reference toFIG. 2which diagrammatically shows a plan view of the test fixture10, the first and second planar antennas12,14are suitably constructed as first and second asymmetrical beam-tilted slot antennas, such as the illustrative asymmetrical beam-tilted double slot antennas. The test fixture10includes (or, viewed alternatively, is supported by) a substrate wafer or chip50on which the various components12,14,16are fabricated. The substrate wafer or chip50supporting the various components12,14,16may, for example, comprise GaAs or high resistivity (high-res) silicon or GaN or InP, although other THz and/or mmW-compliant substrate materials are contemplated. In some embodiments, the DUT8is also fabricated on the same substrate wafer or chip50on which the various components12,14,16are fabricated. In such an embodiment, the test fixture10is an integrated circuit including (in this embodiment) the components12,14,16and the DUT8, suitably formed by monolithically fabricating on the substrate wafer or chip50the DUT8, the first and second planar antennas12,14, and a waveguide16connecting the first planar antenna12and the second planar antenna14with the DUT8.

As previously mentioned, in the illustrative embodiment ofFIG. 1the test fixture10is disposed on the planar back side44of the unitary lens40. More particularly, as seen inFIG. 1, in this illustrative embodiment the substrate wafer or chip50of the test fixture10is disposed on the planar second side of the unitary lens40. This allows the DUT8to be accessed, for example to apply an optional DC bias. The disclosed THz and/or mmW test bed is wireless in that no wired connections are used to inject or receive THz and/or mmW signals. However, it is contemplated to employ a wired DC bias connection to the DUT8, such as wire bonds or, in the illustrative example ofFIG. 2, DC probes52that are configured to contact the DUT8to apply a DC bias to the DUT8.

The THz and/or mmW test bed of illustrativeFIG. 1effectively couples the transmitted THz and/or mmW power into and out of the DUT8. The transmitting and receiving beams of the horn antennas20,30are effectively coupled into the hemispherical lens40, and focused onto the device plane using an the off-axis excitation. See Filipovic et al., “Off-axis properties of silicon and quartz dielectric lens antennas”, IEEE Trans. Microwave Theory and Tech., vol. 45, no. 5, pp. 760-766, May 1997; Trichopoulos et al., “A novel approach for improving off-axis pixel performance of THz focal plane arrays,”IEEE Trans. Microw. Theory&Tech, vol. 58, no. 7, pp. 2014-2021, July 2010. The two additional planar THz and/or mmW antennas12,14are provided to couple the THz and/or mmW radiation into the test device ports. The planar THz and/or mmW antennas12,14are designed to transmit and receive from the same off-axis directions as the external horns20,30that are coupled with the ports of the VNA26. As discussed Trichopoulos et al., supra, the design flexibility afforded by the double slot antennas (see Filipovic et al., supra) allows for the desired beam-corrected/beam-tilted broadband operation, which enhances the coupling efficiency (by more than 10 dB).

With particular reference toFIG. 2, the planar waveguide16is suitably a co-planar waveguide (CPW), and the planar THz and/or mmW antennas12,14are suitably broadband double slot antenna having a “butterfly” shaped slot design, as described in Topalli et al., “An indirect impedance characterization method for monolithic THz antennas,” inIEEE Int. Symposium on Antennas and Propagation, pp. 1882-1884, July 2011. The two asymmetrical beam-tilted butterfly slot antennas12,14can be integrated into the CPW environment, yielding a flexible topology that allows for the optional integration of matching circuitry (to optimize device response) into the CPW16, along with DC biasing connections (e.g. the DC probes52). Various standard active and passive circuits, such as filters and matching networks, can also be integrated using this topology. For example, the test fixture10of illustrativeFIG. 2includes a high impedance inductive line60and a low-impedance capacitive line62.

With reference toFIGS. 3-5, calibration and initial validation of the disclosed non-contact THz and mmW probe is described.FIG. 3illustrates a two-port network model of the measurement path of the test fixture10. The DUT8is modeled by a matrix

[A′B′C′D′].
The “Measurement plane for Port 1” designates the connection of the first planar antenna12to the waveguide16, while the “Measurement plane for Port 2” designates the connection of the second planar antenna14to the waveguide16. The measurement path from the first planar antenna12to the DUT8is characterized by a matrix161which in the illustrative two-port network model is represented by a matrix

[ABCD].
The measurement path from the DUT8to the second planar antenna14is characterized by a matrix162which in the illustrative two-port network model is represented by a matrix

[DBCA].
The measured S-parameters for the test fixture10including the DUT8are suitably represented by a matrix

[AmBmCmDm].
FIG. 4illustrates the two-port network model for a short circuit fixture which is the same as the test fixture10ofFIG. 2, except that the DUT8is replaced by a short circuit. The measured S-parameters for the short circuit fixture are suitably represented by a matrix [Ssh].FIG. 5illustrates the two-port network model for a standard load fixture which is the same as the test fixture10ofFIG. 2, except that the DUT8is replaced by a standard load (namely a 50-ohm resistance in the illustrative standard load fixture ofFIG. 5). The measured S-parameters for the standard load are suitably represented by a matrix [Sld].

For an accurate device characterization, the repeatable artifacts introduced by the probes are preferably eliminated from the measurements, and the reference planes moved to the device terminals. As shown inFIGS. 3-5, the two-port calibration artifact (or the error box) between the VNA26and the DUT8can be characterized using two separate measurements, e.g. by replacing the DUT8with a short (the short circuit text fixture ofFIG. 4) and by replacing the DUT8with a known, i.e. standard, load termination (a 50 ohm resistive load in illustrativeFIG. 5). After the test device measurement is taken (that is, the S-parameters

[AmBmCmDm]
acquired using the contactless test bed and the VNA26), the calibration artifacts are de-embedded using the short measurement [Ssh] and the standard load measurement [Sld] to obtain the corrected device characteristics.

With reference toFIGS. 6 and 7, computer simulations were performed using the calibration approach outlined inFIGS. 3-5, and initial results are summarized for the non-contact THz and mmW characterization approach. For this purpose, a simplified test device comprising a 150 ohm resistor was integrated into a simplified CPW setup. For these simulations, the contactless test bed did not include the hemispherical lens40, as diagrammatically shown in the inset of each ofFIGS. 6 and 7. Open-ended THz waveguides were used to couple into the two slot dipole antennas attached to the device ports.FIG. 6shows results for a design for a 0.9 THz to 1 THz band, whileFIG. 7shows results for a design for a 750 GHz to 850 GHz. As seen inFIG. 6, the extracted test device impedances show a fairly good agreement for two separate designs for in the 0.750-1 THz band.

With reference toFIG. 8, another THz characterization system is shown, which is similar to that ofFIG. 1and includes the THz probes24,34connected to a VNA (not shown inFIG. 8, but suitably connected to the VNA26as shown inFIG. 1), spectrum analyzer, or other electronic analyzer which is used to characterize the DUT8in the test fixture10as described with reference toFIGS. 1 and 2. The THz and/or mmW characterization system ofFIG. 8also includes the horn antenna20,30and unitary lens40of the system ofFIG. 1, but in a different physical arrangement. In the arrangement ofFIG. 8, the horn antenna (or, more generally, THz and/or mmW radiator)20is integrally constructed with the THz and/or mmW probe24, and likewise the horn antennal (or, more generally, THz and/or mmW receiver)30is integrally constructed with the THz and/or mmW probe34. These components are mounted on an optical table surface70, optionally on angled supports72,74as shown inFIG. 8. Suitable optics, such as illustrative off-axis parabolic mirrors80designed to redirect the THz and/or mmW beam by 90°, are used to direct probe THz radiation into the lens22focusing THz and/or mmW radiation from the THz and/or mmW radiator20onto the first planar antenna12of the test fixture10to form the probe THz and/or mmW radiation beam18, and to direct the THz and/or mmW signal28emitted by the second planar antenna14from the receiving lens32to the THz and/or mmW receiver30. In the arrangement shown inFIG. 8, the unitary lens40is “upside-down” as compared with its orientation inFIG. 1, so that the planar back side44of the unitary lens40is facing “upward” to form a flat surface on which the test fixture10is suitably disposed. This advantageously enables the DC probes52to be oriented to contact a flat “upper” surface of the DUT8which can be convenient for manipulation of the DC probes52.

As with the characterization apparatus ofFIG. 1, the system ofFIG. 8provides for contactless evaluation of active devices (e.g. DUT8) in the THz and/or mmW regime (0.03-3 THz). The test fixture includes the pair of THz and/or mmW antennas12,14that are fabricated on the substrate wafer or chip50(for example, comprising GaAs or high-res silicon). The THz and/or mmW antennas12,14that are suitably on-chip wideband impedance-matched butterfly-shaped antennas used to couple the THz and/or mmW signals onto the coplanar waveguide (CPW)16device environment which also includes the DUT8. As seen in the upper inset ofFIG. 8, the two complementary THz and/or mmW antennas12,14function as input/output probes and are connected with the CPW16. The mid-section of the CPW line16incorporates either a standard calibration load (seeFIG. 5, which may be a short circuit load as perFIG. 4) or the DUT8, and may include matching circuitry such as the illustrative matching circuitry60,62shown inFIG. 2. The DUT8is optionally monolithically integrated in the middle of the CPW16. The substrate wafer or chip50is placed under (in the configuration ofFIG. 1, or on top of in the configuration ofFIG. 8) the extended-hemispherical lens40to facilitate optical coupling to the external transmitter20and to the THz receiver30. This non-contact topology utilizes the versatility of the CPW environment, and provides the option of integrating matching and stabilization circuitry. Another advantage is that the THz and/or mmW excitation and interrogation of the integrated device (e.g. test fixture10) is facilitated by the planar THz and/or mmW antennas12,14on the same substrate50. The calibration process already described with reference toFIGS. 3-5is suitably applied for the system ofFIG. 8as well.

As previously mentioned, the illustrative horn antennas20,30can be replaced by other suitable THz and/or mmW transmitters/receivers, such as broadband, quasi-optical, photoconductive-switch-based THz radiators synchronized by femto-second pulsed lasers. Broadband butterfly-shaped antennas are suitably used as the first and second planar antennas12,14to provide broad bandwidth operation. In one illustrative embodiment, suitable planar antennas12,14were fabricated on a 400 um-thick GaAs wafer, although other THz and/or mmW-compliant substrates are contemplated.