Terahertz transmitter / receiver and method of manufacturing the same

Abstract

The present disclosure provides a terahertz (THz) transceiver that includes a triple-barrier resonant tunneling diode (TBRTD), a resonator antenna electrically connected to an emitter and a collector of the TBRTD, and a radiating antenna disposed on the resonator antenna and aligned perpendicularly thereto to reduce system size. A method for manufacturing a corresponding THz transceiver is also provided.

Description

[Technical Field]

[0001] The present disclosure relates to transceiver technology. In particular, the present disclosure further relates to a terahertz (THz) transceiver and a method for manufacturing a THz transceiver. [Background technology]

[0002] Non-destructive testing (NDT) is a method for testing the structural and molecular properties of a system without damaging it. NDT methods are widely used in mechanical engineering, civil engineering, materials science, medical fields, etc. In any small testing system, NDT is simple: very small amounts of sensed data are transmitted to an inspection station via a wired or wireless network. However, non-destructive testing of large structures such as coal mines, long-distance pipelines, wind turbine blades, and railways is not only extremely challenging, but also requires sensor fusion of different non-destructive technologies.

[0003] In recent years, automated NDT integrated with sensor fusion technology has become popular in many industries due to the advantages of testing large structures from remote stations. Industries have deployed artificial intelligence (AI), the Internet of Things (IoT), and cloud computing to perform automated NDT using sensor fusion. The bottleneck of performing automated NDT from a remote station is that wireless network bandwidth limits the number of sensors that can be wirelessly connected in the fusion network.

[0004] The future is becoming wireless, and wireless bandwidth and data transfer speed are key aspects for creating ultra-big sensor fusion networks for autonomous NDT from remote stations. Recent developments in IoT, AI, cloud computing, virtual reality (VR), augmented reality (AR), and autonomous vehicles are known to rapidly transfer large amounts of data. Furthermore, in the field of wirelessly connected sensors and systems, performance primarily depends on wireless speed. Specifically, wireless speed in short-range wireless networks is a key factor for the advancement of autonomous NDT and sensor fusion in the future wireless world.

[0005] In light of the above, terahertz (THz) electromagnetic waves are suitable for carrying several gigabytes of data per second, and terahertz beams are directional. Terahertz rays are not easily ionized and are non-invasive. Furthermore, THz rays can penetrate many dielectric materials, and many chemical fingerprints, such as those of explosives, lie within the terahertz spectrum, which extends the applications of terahertz waves from communications to non-destructive analysis of solids. Summary of the Invention

[0006] The present disclosure provides a terahertz (THz) transceiver that includes a triple-barrier resonant tunneling diode (TBRTD) having an emitter and a collector, a resonator antenna electrically connected to the emitter and the collector of the TBRTD, and a radiating antenna disposed above and aligned perpendicular to the resonator antenna.

[0007] The present disclosure further provides a method of fabricating a THz transceiver, including the steps of: forming a TBRTD having an emitter and a collector; forming a resonator antenna electrically connected to the emitter and collector of the TBRTD; and forming a radiating antenna disposed above and vertically aligned with the resonator antenna.

[0008] The present disclosure provides a THz transceiver and a method for fabricating a THz transceiver that overcomes the challenges associated with developing a compact, efficient, and low-cost terahertz transceiver for short-range, high-speed communication and non-destructive analysis using a portable terahertz scanner. The THz transceiver can be produced using mature planar integrated circuit (IC) manufacturing processes, enabling IC-level packaging of the transceiver as the size scales down to the micrometer scale. The THz transceiver also eliminates the need for silicon (Si) lenses used for THz extraction in conventional transceiver devices. The electronically reconfigurable frequency-tuning antenna in the provided THz transceiver not only helps extract terahertz radiation into free space but also tunes the output frequency in portable terahertz scanners for NDT. Furthermore, the THz transceiver can be installed with IoT devices, sensor fusion networks, and AR and VR devices to support high-speed data transfer in automated non-destructive testing applications.

[0009] Some of the advantages of the THz transceiver provided by the present disclosure are listed below.

[0010] Reduced system size: The small, compact TBRTD combined with a reconfigurable fractal radiating antenna with a ferroelectric substrate allows for a very small overall transceiver footprint (less than approximately 1 x 1 mm including the antenna) for 0.2-0.6 THz operation.

[0011] Tunable frequency and wideband operation: The provided THz transceiver utilizes a wideband TBRTD and a reconfigurable radiating antenna that enables very high Q (>100) narrowband continuous tuning and wideband (0.2-0.6 THz) operation.

[0012] Batch processing and price reduction: One way to reduce the price is to make the device simpler, easier to manufacture, and also utilize batch processing, making the device compatible apart from all the technical issues that need to be addressed. The THz transceiver provided provides a simpler, more cost-effective, and compatible device that fully meets the necessary market requirements and can be easily adopted to different specifications and standards.

[0013] Applications and Advancements: The provided THz transceivers overcome existing limitations in cost and portability, enabling applications such as portable THz scanners for biomedical imaging and portable THz spectrometers for nondestructive analysis for industrial and biomedical applications. Furthermore, the terahertz spectrum contains the chemical fingerprints of many toxic substances and explosives. Therefore, the provided THz transceivers are useful in many areas, such as security and screening applications in airports, for example, performing nondestructive analysis of explosives. [Brief explanation of the drawings]

[0014] The present disclosure can be more fully understood by reading the following description of the embodiments in conjunction with the accompanying drawings, in which: [Figure 1] FIG. 1 is a perspective view of a THz transceiver according to one embodiment of the present disclosure. [Figure 2] FIG. 2 is a perspective view of a THz transceiver according to one embodiment of the present disclosure. [Figure 3] FIG. 3 is a perspective view of a THz transceiver according to another embodiment of the present disclosure. [Figure 4] FIG. 4 is a top view of a grating reflector for a THz transceiver according to one embodiment of the present disclosure. [Figure 5] FIG. 5 is a cross-sectional view of a portion of a THz transceiver according to one embodiment of the present disclosure. [Figure 6] FIG. 6 is an exemplary graph illustrating voltage versus current density characteristics of a TBRTD according to one embodiment of the present disclosure. [Figure 7]FIG. 7 is an exemplary graph illustrating estimated device capacitance versus maximum oscillation frequency characteristics of a TBRTD according to one embodiment of the present disclosure. [Figure 8] FIG. 8 is a schematic diagram illustrating a frequency-tunable fractal antenna for a THz transceiver according to different embodiments of the present disclosure. [Figure 9] FIG. 9 is a schematic diagram illustrating a frequency-tunable fractal antenna for a THz transceiver according to different embodiments of the present disclosure. [Figure 10] FIG. 10 is a schematic diagram illustrating a frequency-tunable fractal antenna for a THz transceiver according to different embodiments of the present disclosure. [Figure 11] FIG. 11 is a schematic diagram illustrating a frequency-tunable fractal antenna for a THz transceiver according to different embodiments of the present disclosure. [Figure 12] FIG. 12 is an exemplary graph illustrating frequency shifts of a frequency-tunable fractal antenna in a THz transceiver according to different embodiments of the present disclosure. [Figure 13] FIG. 13 is an exemplary graph illustrating frequency shifts of a frequency-tunable fractal antenna in a THz transceiver according to different embodiments of the present disclosure. [Figure 14A] FIG. 14A is a cross-sectional view illustrating a method flow for fabricating a THz transceiver according to an embodiment of the present disclosure. [Figure 14B] FIG. 14B is a cross-sectional view illustrating a method flow for fabricating a THz transceiver according to an embodiment of the present disclosure. [Figure 14C] FIG. 14C is a cross-sectional view illustrating a method flow for fabricating a THz transceiver according to an embodiment of the present disclosure. [Figure 14D] FIG. 14D is a cross-sectional view illustrating a method flow for fabricating a THz transceiver according to an embodiment of the present disclosure. [Figure 14E] FIG. 14E is a cross-sectional view illustrating a method flow for fabricating a THz transceiver according to an embodiment of the present disclosure. [Figure 14F] FIG. 14F is a cross-sectional view illustrating a method flow for fabricating a THz transceiver according to an embodiment of the present disclosure. [Figure 14G]14G is a cross-sectional view illustrating a method flow for fabricating a THz transceiver according to an embodiment of the present disclosure. [Figure 15A] FIG. 15A is a cross-sectional view illustrating a method flow for fabricating a fractal antenna according to an embodiment of the present disclosure. [Figure 15B] 15B is a cross-sectional view illustrating a method flow for fabricating a fractal antenna according to an embodiment of the present disclosure. [Figure 15C] 15C is a cross-sectional view illustrating a method flow for fabricating a fractal antenna according to an embodiment of the present disclosure. [Figure 15D] FIG. 15D is a cross-sectional view illustrating a method flow for fabricating a fractal antenna according to an embodiment of the present disclosure. [Figure 15E] 15E is a cross-sectional view illustrating a method flow for fabricating a fractal antenna according to an embodiment of the present disclosure. [Figure 15F] 15F is a cross-sectional view illustrating a method flow for fabricating a fractal antenna according to an embodiment of the present disclosure. [Figure 15G] 15G is a cross-sectional view illustrating a method flow for fabricating a fractal antenna according to an embodiment of the present disclosure. [Figure 15H] FIG. 15H is a cross-sectional view illustrating a method flow for fabricating a fractal antenna according to an embodiment of the present disclosure. [Figure 15I] FIG. 15I is a cross-sectional view illustrating a method flow for fabricating a fractal antenna according to an embodiment of the present disclosure. [Figure 15J] FIG. 15J is a cross-sectional view illustrating a method flow for fabricating a fractal antenna according to an embodiment of the present disclosure. [Figure 15K] FIG. 15K is a cross-sectional view illustrating a method flow for fabricating a fractal antenna according to an embodiment of the present disclosure. [Figure 15L] FIG. 15L is a cross-sectional view illustrating a method flow for fabricating a fractal antenna according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0015] The following detailed description is used to explain the present disclosure. Those skilled in the art can easily conceive other advantages and effects of the present invention based on the disclosure in this specification. The present disclosure can also be implemented or applied as described in different embodiments. The following description for implementing the present disclosure can be modified or changed for different aspects and applications without departing from the spirit and scope thereof.

[0016] 1 and 2 are perspective views of a THz transceiver 100 according to one embodiment of the present disclosure. The THz transceiver 100 includes a grating reflector 110, a substrate 120, a buffer layer 130, a passivation layer 140, a spacer layer 150, a TBRTD 160, a resonator antenna 170, and a radiating antenna 180. In FIG. 1, the radiating antenna 180 and the spacer layer 150 have been removed to more clearly show the resonator antenna 170. The substrate 120 is disposed on the grating reflector 110. The buffer layer 130 is disposed on the substrate 120. The passivation layer 140 is disposed on the buffer layer 130. The TBRTD 160 is embedded in the passivation layer 140. A major portion of the resonator antenna 170 is disposed on the passivation layer 140. The top electrode of resonator antenna 170 is electrically connected to the emitter end of TBRTD 160, and the bottom electrode of resonator antenna 170 is electrically connected to the collector end of TBRTD 160. The top electrode of resonator antenna 170 is embedded in passivation layer 140, and the bottom electrode of resonator antenna 170 is disposed on buffer layer 130 and is embedded in or covered by passivation layer 140. Spacer layer 150 is disposed on passivation layer 140 and resonator antenna 170. Radiating antenna 180 is disposed on spacer layer 150.

[0017] In this embodiment, the resonator antenna 170 and the radiating antenna 180 are fractal antennas shaped according to the same fractal curve or pattern. Therefore, the radiating antenna 180 has the same shape and size as the main body of the resonator antenna 170. Furthermore, the radiating antenna 180 and the main body of the resonator antenna 170 are vertically aligned. For example, the resonator antenna 170 and the radiating antenna 180 shown in FIGS. 1 and 2 are both shaped according to a Hilbert curve. In other embodiments, the resonator antenna 170 and the radiating antenna 180 may be shaped according to another fractal curve or pattern, such as a Koch curve, a Peeno curve, a Sierpinski gasket, or a Minkowski geometry.

[0018] In this embodiment, the grating reflector 110 is made of metal and dielectric. The substrate 120 is made of indium phosphide (InP). The buffer layer 130 is made of InP. 0.53 Ga 0.47 The passivation layer 140 is made of As. The passivation layer 140 is made of silicon dioxide (SiO2). The purpose of the passivation layer 140 is to protect the unexposed portions of the THz transceiver 100 during etching in the manufacturing process. Therefore, the material of the passivation layer 140 can vary depending on the etchant. The spacer layer 150 serves as a separator between the resonator antenna 170 and the radiating antenna 180. The spacer layer 150 should be transparent in the terahertz region. Therefore, the spacer layer 150 is preferably made of a polymer such as cyclic olefin copolymer (COC) or benzocyclobutene (BCB). The resonator antenna 170 and the radiating antenna 180 may be made of any conductive material, such as a metal.

[0019] For transmitter operation, quantum mechanical resonant tunneling in the TBRTD 160 is a fast process that induces THz transients within the TBRTD 160. The inductance of the resonator antenna 170 compensates for the parasitic capacitance of the TBRTD 160, thus creating a resonance for THz oscillation based on the THz transients. The THz electromagnetic waves generated from the resonator antenna 170 are inductively coupled to the radiating antenna 180, which then radiates them into free space.

[0020] In receiver operation, the radiating antenna 180 functions as a receiving antenna that absorbs the THz signal incident on it. The local electromagnetic field of the THz signal at the radiator / receiver antenna 180 inductively couples with the resonator antenna 170. The electromagnetic field at the resonator antenna 170 induces a THz current flow through the TBRTD 160 by electrical rectification.

[0021] Because resonant tunneling diodes (RTDs) are the only electronic terahertz sources with the highest oscillation frequencies at room temperature, and triple-barrier RTDs (TBRTDs) offer higher direct current (DC) to radio frequency (RF) conversion efficiency than conventional double-barrier RTDs (DBRTDs), the THz transceiver 100 employs a TBRTD 160 as the terahertz source.

[0022] Conventional RTD THz transceivers use narrowband antennas, such as slot and patch antennas, which are extremely narrowband, and the output spectrum of these devices is not tunable. In contrast, the THz transceiver 100 provided by the present disclosure uses a high-gain, omnidirectional, wideband fractal antenna, and the output spectrum of the THz transceiver 100 is tunable. The fractal antennas, i.e., the resonator antenna 170 and the radiating antenna 180 of the THz transceiver 100, are capable of emitting and receiving THz radiation from 200 GHz to 600 GHz.

[0023] In addition, in conventional RTD THz transceivers, 98% of the generated THz power is trapped within the substrate due to total internal reflection (TIR) ​​within the substrate caused by the substrate's high refractive index, and therefore the generated power is wasted and converted into unwanted heat. Therefore, conventional RTD THz transceivers use a silicon lens on the back side of the substrate (the side facing away from the RTD) to extract as much power as possible. However, the adhesive layer between the substrate and the silicon lens causes a large loss of extracted power. Silicon lenses require precise alignment and are bulky and expensive.

[0024] In contrast, the grating reflector 110 used on the backside of the substrate 120 of the THz transceiver 100 not only eliminates the use of a silicon lens, but also reduces the TIR effect within the substrate 120 and improves DC-to-RF conversion efficiency. As shown in FIG. 4 , which is a top view of a grating reflector 110 according to an embodiment of the present disclosure, the grating reflector 110 is formed by alternating interleaved metal strips 112 and dielectric strips 114. The combined width of each adjacent pair of metal strips 112 and dielectric strips 114 is much smaller than the wavelength of the THz electromagnetic waves generated from the resonator antenna 170. In this configuration, the interleaved metal strips 112 and dielectric strips 114 periodically vary the refractive index at the interface between the substrate 120 and the grating reflector 110, thus reducing the TIR within the substrate 120 and reflecting the emitted power to the front side of the substrate 120 (the side facing the TBRTD 160). Therefore, the grating reflector 110 improves THz radiation at the front side of the substrate 120. Additionally, the metal strips 112 of the grating reflector 110 act as a heat sink to dissipate heat generated within the substrate 120 .

[0025] Note that the grating reflector 110 is not limited to the configuration shown in Fig. 4. For example, in another embodiment, the grating reflector 110 may be formed by two-dimensionally interleaved metal and dielectric patches based on a checkerboard pattern, in which the combined width of each adjacent pair of metal and dielectric patches measured along either of the two dimensions is much smaller than the wavelength of the THz electromagnetic waves generated from the resonator antenna 170.

[0026] FIG. 3 is a perspective view of a THz transceiver 300 according to an embodiment of the present disclosure, which is an alternative design to the previously described THz transceiver 100. The main portion of the resonator antenna 170 of the THz transceiver 300 is fabricated on the substrate 120 or buffer layer 130. In FIG. 3, the spacer layer 150 and the radiating antenna 180 have been removed, and only a small portion of the passivation layer 140 is shown, to more clearly show the TBRTD 160 and the resonator antenna 170. In fact, the passivation layer 140 of the THz transceiver 300 may have approximately the same size as its counterpart in FIG. 1, such that the passivation layer 140 covers the resonator antenna 170, and the THz transceiver 300 includes the spacer layer 150 disposed on the passivation layer 140 and the radiating antenna 180 fabricated on the spacer layer 150.

[0027] 5 is a cross-sectional view of a portion of a THz transceiver 500 according to one embodiment of the present disclosure. The THz transceiver 500 includes all of the components and layers of the THz transceiver 100 shown in FIGS. 1 and 2. The THz transceiver 500 further includes a bottom contact layer 510 disposed between the buffer layer 130 and the TBRTD 160, a top contact layer 520 formed on the TBRTD 160, a bottom contact metal 515 formed on the bottom contact layer 510, and a top contact metal 525 formed on the top contact layer 520. The bottom contact metal 515 and the top contact metal 525 are formed by sputtering gold and are terminal portions of the resonator antenna 170.

[0028] 5, the TBRTD 160 has a nine-layer stack including, from bottom to top, a collector layer 161, a spacer 162, a collector barrier 163, a quantum well (collector well) 164, a primary barrier 165, another quantum well (emitter well) 166, an emitter barrier 167, a spacer 168, and an emitter layer 169. Table 1 below lists the material, thickness, and molar concentration of silicon doping for each layer from the top contact layer 520 to the buffer layer 130 in FIG. 5.

[0029] [Table 1]

[0030] In a traditional double-barrier RTD or DBRTD, the emitter and collector barriers are identical (same barrier material and thickness) and the device structure is symmetrical, avoiding rapid thermal leakage current and increasing tunneling current.

[0031] In contrast, the triple barrier TBRTD 160 proposed by the present disclosure includes more quantum wells and barriers, increasing well charge and peak current and reducing peak voltage. Furthermore, the TBRTD 160 includes a non-identical primary barrier 165. As shown in Table 1, the collector barrier 163 and the emitter barrier 167 have the same material and thickness, but the primary barrier 165 is formed of a different material and has a different thickness. Furthermore, the collector well 164 and the emitter well 166 are also asymmetric due to their different thicknesses. Therefore, the aforementioned asymmetric structure increases the tunneling current and increases the maximum operating frequency limit.

[0032] As shown in Table 1, the main barrier 165 is In 0.52 Al 0.48 The collector barrier 163 and the emitter barrier 167 are made of AlAs. All other layers shown in Table 1 are made of In. 0.53 Ga 0.47The TBRTD 160 employs a combination of InGaAs / InAlAs / AlAs materials because this material system provides better RTD characteristics. The spacers 162 and 168 are made of undoped InGaAs to avoid charge carrier diffusion from the highly doped layers. 0.53 Ga 0.47 As.

[0033] The TBRTD160 is a simulated 440kA / cm 2 The theoretically calculated maximum extractable output power of the TBRTD160 is 1 μm. 2 The output power is approximately 250 μW at 0.95 THz for a device area of ​​1.5 mm, which is much higher than the previously reported output power of conventional TBRTDs. The non-identical triple-barrier structure of the TBRTD160 exhibits a ΔV of 0.41 V and a ΔI of 0.0033 A, where ΔV and ΔI are the voltage and current, respectively, in the negative differential resistance (NDR) region of the TBRTD160. The peak-to-valley current ratio (PVCR) is approximately 4.71. Compared with conventional TBRTDs, the peak current and peak voltage of the TBRTD160 are reduced without compromising the PVCR, while simultaneously increasing the DC-to-RF conversion efficiency. The maximum oscillation frequency of the TBRTD160 is 0.95 THz. The theoretically estimated parasitic capacitance of the TBRTD160 is c n =21.3fF. The series resistance of the TBRTD160 is R s = 3.25 Ω. The reciprocal of the negative conductance of the TBRTD160 is R n =18.66Ω.

[0034] Figure 6 shows the 1 μm 2 7 is an exemplary graph showing numerically simulated voltage versus current density characteristics of a TBRTD 160 having a device area of ​​1 μm. 2 1 is an exemplary graph illustrating the maximum oscillation frequency characteristic versus estimated device capacitance for a TBRTD 160 having a device area of ​​100 .mu.m.

[0035] In this embodiment, the resonator antenna 170 and the radiating antenna 180 of the THz transceiver 500 are fractal antennas, which utilize fractal technology to enable compact antennas and the integration of multiple bands. Fractal antennas have desirable properties, such as space-filling, self-similarity, fractal dimensions, infinite complexity, mechanical simplicity, and robustness, making them particularly advantageous for achieving compactness, wideband, and multi-band characteristics with better efficiency. The space-filling property is used to reduce antenna size. The self-similarity is used to achieve multi-band resonator antennas. The number of geometric repetitions of the resonator antenna 170 and the radiating antenna 180 is based on their operating wavelengths.

[0036] Furthermore, the radiating antenna 180 of the THz transceiver 500 is a fractal antenna that is reconfigurable to extend its operating frequency range. The radiating antenna 180 can be adjusted to achieve either reconfigurability or tunability in the desired frequency range for wireless communication.

[0037] In one embodiment, for a large frequency shift, a large section of electrical length or a large segment of the fractal pattern can simply be disconnected from the radiating antenna 180, thus reducing the overall size of the radiating antenna 180 and generating an upward frequency shift. On the other hand, more electrical length or more fractal patterns can be connected to the radiating antenna 180, thus increasing the overall size of the radiating antenna 180 and generating a downward frequency shift. The radiating antenna 180 can include at least one switch embedded in the fractal curve or fractal pattern of the radiating antenna 180. The at least one switch can be implemented by a diode or transistor that connects and disconnects one or more sections or segments of the radiating antenna 180 to reconfigure the radiating antenna 180 for a frequency shift. For example, in one embodiment, the radiating antenna 180 can be switched between a one-segment fractal curve 800 of FIG. 8 and a two-segment fractal curve 900 of FIG. 9. When the radiating antenna 180 is switched to the one-segment fractal curve 800 of Fig. 8, its reflection coefficient S11 is plotted as curve 1210 of Fig. 12. When the radiating antenna 180 is switched to the two-segment fractal curve 900 of Fig. 9, its reflection coefficient S11 is plotted as curve 1220 of Fig. 12.

[0038] In one embodiment, for an intermediate frequency shift, fewer fractal patterns or shorter electrical lengths can be disconnected from or connected to the radiating antenna 180 by controlling a switch embedded in the radiating antenna 180. This effect can decrease the electrical length of the radiating antenna 180 and increase the operating frequency, or vice versa. For example, in one embodiment, the radiating antenna 180 can be further switched between fractal curve 1000 in FIG. 10 and fractal curve 1100 in FIG. 11. When the radiating antenna 180 switches from fractal curve 900 in FIG. 9 to fractal curve 1000 in FIG. 10, three arms are disconnected from each fractal segment, increasing the electrical length. The resulting reflection coefficient S11 is plotted as curve 1230 in FIG. 12. A downward (leftward) frequency shift of approximately 0.02 THz is observed. If the radiating antenna 180 is switched to the fractal curve 1100 of Figure 11 and has a larger cut and electrical length reduction, the reflection coefficient S11 is plotted as curve 1240 of Figure 12. Here, an upward (rightward) frequency shift is observed.

[0039] In another embodiment, similar to the radiating antenna 180, the resonator antenna 170 may include at least one switch implemented by a diode or transistor for connecting and disconnecting one or more sections, segments, or arms of the resonator antenna 170 to reconfigure the resonator antenna 170 for large and intermediate frequency shifts.

[0040] In another embodiment, both the resonator antenna 170 and the radiating antenna 180 include switches for large and medium frequency shifts.

[0041] In one embodiment, for fine frequency shifting or continuous frequency tuning, the spacer layer 150 below the radiating antenna 180 includes a ferroelectric material, such as a polymer dispersed liquid crystal (PDLC), whose dielectric constant changes as the electric field applied to the ferroelectric material changes. Unlike the previously described fractal pattern reconstructions that rely heavily on fractal patterns, where the frequency shift is more discrete, voltage-induced dielectric constant changes in the radiating antenna 180 can produce much more continuous and fine changes in the operating frequency.

[0042] An example of this frequency shift due to dielectric constant change using a spacer layer 150 made of PDLC on a radiating antenna 180 is shown in Figure 13, where the frequency shift is due to the liquid crystal in the spacer layer 150 changing from an ordinary polarization state (corresponding to curve 1310) to an extraordinary polarization state (corresponding to curve 1320). The operating frequency of the radiating antenna 180 changes proportionally to the dielectric constant of the PDLC in the spacer layer 150.

[0043] In another embodiment, the substrate 120, buffer layer 130, or passivation layer 140 beneath the resonator antenna 170 comprises a ferroelectric material such as PDLC for fine frequency shifting or continuous frequency tuning of the resonator antenna 170.

[0044] In another embodiment, the substrate 120, buffer layer 130 or passivation layer 140 under the resonator antenna 170 and the spacer layer 150 under the radiating antenna 180 both comprise a ferroelectric material such as PDLC for fine frequency shifting or continuous frequency tuning of the resonator antenna 170 and the radiating antenna 180.

[0045] The key process in the overall fabrication of the THz transceiver 500 is the epitaxial growth of the quantum structure. Molecular beam epitaxy (MBE) technology is used to realize the quantum structure of the TBRTD 160. See FIG. 5 or FIG. 14A. First, a 3 μm thick In 0.53 Ga 0.47An As buffer layer 130 is grown on a semi-insulating Fe-doped InP substrate 120 to achieve perfectly lattice-matched growth layers. Next, a bottom contact layer 510, a layer of TBRTD 160, and a top contact layer 520 are grown from bottom to top. The quality and precision of the as-grown layers are verified using high-resolution X-ray diffraction (HR-XRD) or low-temperature photoluminescence spectroscopy (LT-PT).

[0046] The fabrication steps required to realize the THz transceiver 500 are shown in Figures 14A-14G. After growing and characterizing the TBRTD 160, the InP wafer undergoes a series of fabrication steps. Because the TBRTD 160 structure is large enough to use photolithography, all necessary patterns are created using an MA-6 Aligner tool with a 365 nm UV light source. The first step, as shown in Figure 14A, is to deposit the top contact metal 525 onto the top contact layer 520 using an E-gun evaporation or sputtering tool. A Ti / Pd / Au (20 / 30 / 150 nm thick) thin film combination is used as the top contact metal 525 because it provides a very low specific contact resistance.

[0047] The next step is to deposit bottom contact metal 515, where a first mesa etch is performed to etch down to the bottom contact layer 510, as shown in Figure 14B. Figure 14C shows the bottom contact metal 515 deposited on the bottom contact layer 510 after the first mesa etch. A Ti / Pd / Au thin film combination is also used as the bottom contact metal 515. A second mesa etch is performed to etch down to the InP substrate 120, as shown in Figure 14D. A H3PO4:HO2:HO (1:1:38) acid solvent mixture is used to complete the two mesa etching steps at an etch rate of approximately 100 nm / min.

[0048] The next step is to spin-coat or deposit a passivation layer 140 to protect the quantum structures of the TBRTD 160, as shown in FIG. 14E. The passivation layer 140 can be made of a polymer such as polyimide PI-225, cyclic olefin copolymer (CoC), or benzocyclobutene (BCB). A via for connection to the resonator antenna 170 is opened in the passivation layer 140 to expose the top contact metal 525. After the via opening, a resonator antenna metal 175 (Ti / Pd / Au) is deposited on the passivation layer 140, and a resonator antenna metal 174 (Ti / Pd / Au) is deposited on the buffer layer 130, as shown in FIG. 14F. The resonator antenna metals 174 and 175 constitute the resonator antenna 170. The resonator antenna metal 174 is connected to the bottom contact metal 515, and the resonator antenna metal 175 is connected to the top contact metal 525.

[0049] Next, as shown in FIG. 14G, a polymer is spin-coated on the resonator antenna metal 175 to form the spacer layer 150. The thickness of the spacer layer 150 is optimized based on the mutual coupling between the resonator antenna 170 and the radiating antenna 180. Finally, as shown in FIG. 14G, the radiating antenna metal 185 is deposited on the spacer layer 150. The radiating antenna metal 185 constitutes the radiating antenna 180. The thin-film technology-based radiating antenna 180 is introduced to maximize THz radiation on the air-side (front side) of the substrate 120.

[0050] 15A-15L are cross-sectional views illustrating a method for fabricating a fractal antenna according to an embodiment of the present disclosure. First, as shown in FIG. 15A, a gold layer 1520 is deposited on a glass layer 1510. Then, as shown in FIG. 15B, a polymer layer 1530 is spin-coated onto the gold layer 1520. Next, as shown in FIG. 15C, the polymer layer 1530 is irradiated with ultraviolet light to form liquid crystal droplets in the polymer layer 1530, converting the polymer layer 1530 into a PDLC layer. In the PDLC layer 1530, the polymer is the host material and the liquid crystal is the active material. The fabrication temperature at this stage should be kept below the glass transition temperature of the polymer to maintain the structural morphology.

[0051] Next, as shown in Figure 15D, the side regions of the PDLC layer 1530 are covered with tape 1540, and then, as shown in Figure 15E, another gold layer 1550 is deposited on the PDLC layer 1530 and tape 1540, and then tape 1540 and a portion of gold layer 1550 on tape 1540 are removed. Then, as shown in Figure 15F, an aluminum layer 1560 is deposited on the gold layer 1520, the PDLC layer 1530, and the remaining portions of gold layer 1550. The metal layers, i.e., gold layers 1520, 1550, and aluminum layer 1560, may be deposited by a low-temperature deposition method such as sputtering.

[0052] Next, as shown in Figure 15G, a photoresist layer 1570 is deposited on the aluminum layer 1560, and then a fractal pattern is formed in the photoresist layer 1570 by photolithography as shown in Figure 15H, and then the aluminum layer 1560 is etched with an aluminum etchant, and then the gold layer 1550 is etched with a gold etchant such as trifluoroacetic acid (TFA). Thus, the same fractal pattern is formed in the aluminum layer 1560 and the gold layer 1550 as shown in Figure 15I.

[0053] Next, reactive ion etching (RIE) is performed using oxygen plasma with carbon tetrafluoride (CF4) and argon (Ar) gas to thin the photoresist layer 1570 and etch the PDLC layer 1530 to form the same fractal pattern in the PDLC layer 1530, as shown in Figure 15J. After that, as shown in Figure 15K, the gold layer 1520 is etched using TFA to form the same fractal pattern in the gold layer 1520. Finally, as shown in Figure 15L, the photoresist layer 1570 and the aluminum layer 1560 are removed.

[0054] In an embodiment, the gold layers 1520 and 1550 constitute the aforementioned resonator antenna 170, and the PDLC layer 1530 is the aforementioned passivation layer 140. The aforementioned radiating antenna 180 can be fabricated by a similar process.

[0055] In another embodiment, gold layer 1520 comprises said resonator antenna 170, gold layer 1550 comprises said radiating antenna 180, and PDLC layer 1530 is said spacer layer 150.

[0056] In yet another embodiment, at least one of the gold layers 1520 and 1550 may be replaced with at least one layer of another type of conductor.

[0057] Although several embodiments of the present disclosure have been described in detail above, those skilled in the art may make various modifications and changes to the specific embodiments shown without substantially departing from the teachings and advantages of the present disclosure. Such modifications and changes are encompassed within the spirit and scope of the present disclosure as defined in the appended claims.

Claims

1. a triple barrier resonant tunneling diode (TBRTD) having an emitter and a collector; a resonator antenna electrically connected to the emitter and collector of the TBRTD; a radiating antenna disposed above the resonator antenna and aligned perpendicular to the resonator antenna; Including, the resonator antenna and the radiating antenna are fractal antennas shaped according to the same fractal curve or the same fractal pattern; Terahertz (THz) transceiver.

2. In a transmitter operation, the TBRTD generates a first THz current, the resonator antenna resonates with the TBRTD based on the first THz current to generate THz electromagnetic waves, the THz electromagnetic waves are inductively coupled with the radiating antenna, and are emitted into free space by the radiating antenna; In receiver operation, the radiating antenna absorbs an incident THz signal, the electromagnetic field of the incident THz signal at the radiating antenna inductively couples with the resonator antenna, and the electromagnetic field at the resonator antenna causes a second THz current to flow through the TBRTD due to electrical rectification.

2. The THz transceiver of claim 1.

3. at least one of the resonator antenna and the radiating antenna includes at least one switch embedded in the fractal curve or the fractal pattern of the resonator antenna and / or the radiating antenna; the at least one switch is configured to connect and disconnect portions of the resonator antenna and / or the radiating antenna to shift an operating frequency of the resonator antenna and / or the radiating antenna.

2. The THz transceiver of claim 1.

4. The TBRTD is a collector barrier; a collector well disposed on the collector barrier; a primary barrier disposed over the collector well; an emitter well disposed on the primary barrier; an emitter barrier disposed on the emitter well; Equipped with 2. The THz transceiver of claim 1.

5. The main barrier is In ０．５２ Al ０．４８ Made from As, The collector well and the emitter well are In ０．５３ Ga ０．４７ Made from As, the collector barrier and the emitter barrier are made of AlAs; 5. The THz transceiver of claim 4.

6. the thickness of the emitter well is greater than the thickness of the collector well; the thickness of the collector well is greater than the thickness of the primary barrier; the collector barrier and the emitter barrier have the same thickness; the thickness of the primary barrier is greater than the same thicknesses of the collector barrier and the emitter barrier; 5. The THz transceiver of claim 4.

7. a substrate made of indium phosphide; disposed on the substrate, ０．５３ Ga ０．４７ a buffer layer made of As; a substrate made of silicon dioxide or a polymer and disposed on the buffer layer; a passivation layer in which the TBRTD is embedded; and a spacer layer disposed on the passivation layer and made of a polymer; further comprising:

2. The THz transceiver of claim 1.

8. An In layer disposed between the buffer layer and the TBRTD. ０．５３ Ga ０．４７ a bottom contact layer made of As; An In disposed between the TBRTD and the spacer layer. ０．５３ Ga ０．４７ an upper contact layer made of As; Further comprising: a common doping concentration of silicon in the bottom contact layer and the top contact layer is greater than a common doping concentration of silicon in the collector and emitter of the TBRTD; a common doping concentration of silicon in the collector and emitter of the TBRTD is greater than a doping concentration of silicon in the buffer layer; 8. The THz transceiver of claim 7.

9. the radiating antenna has the same shape and size as a main part of the resonator antenna; a main portion of the resonator antenna is disposed on the substrate, the buffer layer, or the passivation layer; 8. The THz transceiver of claim 7.

10. and a grating reflector disposed below the substrate and made of alternating metal and dielectric materials, wherein the combined width of each adjacent pair of the metal pieces and the dielectric pieces is smaller than the wavelength of the THz electromagnetic waves generated from the resonator antenna.

8. The THz transceiver of claim 7.

11. at least one of the substrate, the buffer layer, the passivation layer, and the spacer layer comprises a ferroelectric material; When an electric field applied to the ferroelectric material is changed, the dielectric constant of the ferroelectric material changes.

8. The THz transceiver of claim 7.

12. forming a triple barrier resonant tunneling diode (TBRTD) having an emitter and a collector; forming a resonator antenna electrically connected to the emitter and the collector of the TBRTD; forming a radiating antenna disposed above and vertically aligned with the resonator antenna; the resonator antenna and the radiating antenna are fractal antennas shaped according to the same fractal curve or the same fractal pattern; A method for fabricating a terahertz (THz) transceiver.

13. The TBRTD is a collector barrier; a collector well disposed on the collector barrier; a primary barrier disposed over the collector well; an emitter well disposed on the primary barrier; an emitter barrier disposed on the emitter well; Equipped with The method of claim 12.

14. The main barrier is In ０．５２ Al ０．４８ Made from As, The collector well and the emitter well are In ０．５３ Ga ０．４７ Made from As, the collector barrier and the emitter barrier are made of AlAs; The method of claim 13.

15. the thickness of the emitter well is greater than the thickness of the collector well; the thickness of the collector well is greater than the thickness of the primary barrier; the collector barrier and the emitter barrier have the same thickness; the thickness of the primary barrier is greater than the same thicknesses of the collector barrier and the emitter barrier; The method of claim 13.

16. forming a grating reflector disposed below the resonator antenna and made of alternating metal and dielectric materials, the combined width of each adjacent pair of the metal pieces and the dielectric pieces being less than the wavelength of the THz electromagnetic waves generated from the resonator antenna; The method of claim 12.

17. providing a ferroelectric material disposed below the resonator antenna or the radiating antenna, the dielectric constant of which changes with a change in an applied electric field; The method of claim 12.

18. forming a first conductor layer; forming a polymer dispersed liquid crystal (PDLC) layer on the first conductor layer; forming a second conductor layer on the PDLC layer; forming an aluminum layer on the second conductor layer; forming a photoresist layer on the aluminum layer; forming a fractal pattern in the photoresist layer, the aluminum layer, the second conductor layer, the PDLC layer, and the first conductor layer by photolithography and etching; removing the photoresist layer and the aluminum layer; the first conductor layer and the second conductor layer constitute the resonator antenna and / or the radiating antenna; The method of claim 12.

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