Hybrid structure for ultra-wideband terahertz generation and reception with semiconductor devices

Abstract

Ultra-wideband hybrid structure (100) for transmitting or receiving high-frequency electrical signals, wherein the hybrid structure (100) comprises: - a substrate (110); - a high-speed semiconductor substrate (105) connected to the substrate (110); - an electrical intermediate connection (115) provided between the substrate (110) and the high-speed semiconductor substrate (105); - an ultra-high-speed device for generating or detecting high-frequency signals, comprising a first access port (P1) and provided on the high-speed semiconductor substrate (105); - a dielectric waveguide structure (DRW) comprising a second access port (P2) providing a characteristic high-pass interface operating over a high-frequency range characterized by a low cutoff frequency f CLstarting in the microwave or millimeter wave range, wherein the waveguide structure (DRW) is provided on the substrate (110) and on the high-speed semiconductor substrate (105), wherein the waveguide structure (DRW) comprises a tapered end facing the first access port (P1) of the ultra-high-speed device; a metal waveguide structure (TSA) providing a characteristic low-pass intermediate that operates over a low frequency range from DC to a high cutoff frequency f CHoperating in the millimeter wave range, wherein the waveguide structure (TSA) is provided on the substrate (110) and on the high-speed semiconductor substrate (105), wherein the metal waveguide structure (TSA) comprises a metal waveguide pattern defining a tapered coupler, preferably a tapered slotted antenna “TSA”, around the tapered end of the dielectric waveguide structure (DRW) and connected to the first access port (P1) of the ultra-high-speed device.

Description

[0001] The present invention relates to a novel structure that enables ultra-wideband high-frequency signal generation and acquisition using semiconductor devices with two distinguishing features: First, the structure of the semiconductor material is shaped to form a high-frequency (HF) waveguide, and second, the structure results from the hybrid integration of a small chip made of III-V semiconductor material for the active device that generates the HF, and part of the transmitting antenna with a larger silicon material for the rest of the antenna and other passive HF components. BACKGROUND OF THE INVENTION

[0002] Terahertz systems operate in the spectral range covering the frequency band between 0.1 and 10 THz, which lies between the microwave and optical frequency bands. The various technologies for generating and acquiring terahertz signals require components integrated on a single chip (an unpackaged, bare chip), which can be either electronic or photonic. Photonics-based systems require optoelectronic converters, with the most common active components being ultrafast photodiodes (primarily PIN photodiodes, PIN-PD, and unit-traveling carrier photodiodes, UTC-PD) and photomixers of a low-temperature grown photoconductive antenna (LTG-PCA) fabricated using III-V semiconductor compound alloys.There is also a wide range of electronics-based components, usually Gunn diodes, IMPATT diodes and resonant tunnel diodes (RTDs), as well as varactor Schottky diode multipliers, which generate high frequencies as higher-order harmonics from a microwave reference source.

[0003] The semiconductor material substrate most commonly used for fabricating photonic and electronic devices is indium phosphide (InP), a III-V semiconductor compound in which the highest operating frequencies have been achieved, making it the preferred substrate for terahertz systems. However, the main disadvantages of this material are its high brittleness and high cost.

[0004] These properties have a significant impact on the dimensions of the chip units, particularly for terahertz generating and receiving devices. In addition to the micrometer-sized component, it is desirable to integrate RF antennas with larger footprints (millimeter-sized). The substrate dimensions cannot be smaller than a minimum size (> 0.5 × 0.2 mm). 2The chip size must be small enough to allow for handling during assembly processes, and it is also not recommended to exceed a maximum size (< 12 mm × 6 mm) due to the fragility of the material. Chips with dimensions outside these limits are of course possible, but at the cost of significantly higher assembly costs and lower yield. These limitations also mean that for systems operating in lower frequency bands of the spectrum (i.e., in the microwave range, from 3 GHz to 30 GHz, or in the millimeter wave range, from 30 GHz to 300 GHz), the chip area is insufficient to monolithically integrate the antenna onto the substrate used for the component.

[0005] A current approach to assembling the chip and antenna is in Fig. Figure 1 shows a 3D model of the assembly (50) comprising an optical fiber aligned to the optical input of an ultrafast photodiode (PD chip), wherein the electrical contact surfaces of the ultrafast photodiode excite a planar tapered-slot antenna (TSA) through a microwave access port (Excitation Port 1). In particular, Figure 1 shows Fig. 1. A high-speed photodiode device fabricated on InP (εr = 12.4) and connected to a TSA-type antenna fabricated on a low-permittivity (εr = 2.2) 110RT / Duroid 5880 substrate. The size of the antenna prevents its integration on the InP substrate; it is then implemented on a suitable RF substrate. This makes the electrical connection between the ultrafast photodiode and the antenna extremely critical, especially since the desired operating frequency range extends into the higher frequency bands.

[0006] Among the various interconnection technologies currently available, the most common in the electronics industry is gold wire bonding. Fig. Figure 2 shows a photograph of an InP-integrated ultrafast photodiode chip (200) in which its electrical contact pads are connected to the antenna access terminal by gold wire bonds. However, the parasitic gold wire series inductance, which is partially attenuated by the use of two bond wires per connection, limits the maximum operating frequency.

[0007] An additional difficulty in the interface between the component chip and the antenna's RF substrate is the difference in permittivity between the substrates. The chip with the higher refractive index generates reflections at this interface, which are particularly detrimental to high-frequency signals. These reflections mean that part of the signal is reflected back to the transmitter, thus reducing the transmitter module's efficiency.

[0008] The present invention overcomes the aforementioned limitations and disadvantages. DESCRIPTION OF THE INVENTION

[0009] The present invention provides a solution to utilize the full bandwidth of an ultra-wideband antenna driven by an ultra-high-speed semiconductor device, making it possible to combine different substrates, overcoming the current limitations of available electrical interconnects that limit the bandwidth for terahertz and subterahertz systems.

[0010] Therefore, the present invention presents a novel structure for ultra-high-speed devices based on a hybrid dielectric conductor guide operating from DC to at least 300 GHz. The present invention proposes an ultra-wideband hybrid structure optimized for high-frequency electrical signals capable of operating up to 340 GHz and capable of achieving higher frequencies by varying the thickness and / or permittivity of the substrates. The ultra-wideband structure enables the coupling of high-frequency signals from high-speed circuits or components fabricated on high-speed semiconductor substrates (e.g., indium phosphide), the dimensions of which may be limited due to technological, manufacturing, or handling constraints (i.e., there are dimensional limitations that prevent the integration of large components).Broadband waveguides or antennas, such as tapered bifilar metal waveguides). The ultra-wideband structure solves this problem, thereby enabling high-performance emission for high-frequency signals. Therefore, the ultra-wideband structure according to the present invention allows most signals for all frequencies within the working bandwidth to be coupled into a single mode, as in the following. Fig. 4A to Fig. Shown in 4D.

[0011] The main aspects of the hybrid structure according to the present invention are: A dielectric waveguide excited in a single-mode regime, which couples signals to / from the component chip in the high-frequency band. This dielectric waveguide structure incorporates a high-pass filter characteristic that provides electrical interfacing for signals with frequencies above a low cutoff frequency (f). CL). The dielectric waveguide comprises a tapered end facing an access terminal (P1) of an ultra-high-speed semiconductor device (electronic or optoelectronic) fabricated on a high-permittivity substrate (e.g., indium phosphide) cleaved into a chip. For example, the dielectric waveguide structure can be designed to operate over a region operating at a low cutoff frequency (f CL) in the microwave range (i.e., between 3 GHz and 30 GHz) or in the millimeter wave range (i.e., between 30 GHz and 300 GHz), for example, at an operating frequency of 60 GHz, which covers a wide frequency range extending into the terahertz wave range (i.e., between 300 and 3000 GHz) and beyond. The dielectric waveguide structure can be provided on the substrate (110) and on the high-speed semiconductor substrate, the waveguide structure comprising a tapered end facing the first access port of the ultra-high-speed device.

[0012] The hybrid structure according to the present invention also includes a metal waveguide structure with a low-pass filter characteristic, which enables a metallic electrical contact to be established with the access port of the ultra-high-speed device, allowing the interfacing operating frequency range to start at low frequencies (i.e., preferably at DC, 0 Hz). This enables the electrical interfacing of signals from 0 Hz up to a high cutoff frequency (f CH) in the millimeter-wave range. For example, the metal waveguide structure can be designed to operate over a range starting at 0 Hz and extending into the millimeter-wave range (i.e., between 30 GHz and 300 GHz, e.g., at an operating frequency of 100 GHz). In a preferred embodiment for broadband operation, this metallic waveguide structure operates over a frequency range starting at a low frequency (i.e., starting at DC, from 0 Hz) and extending over the low cutoff frequency of the dielectric waveguide structure (f CH > f CL , e.g., over the 60 GHz of the previous example).

[0013] The metal waveguide structure can be provided on the substrate and on the high-speed semiconductor substrate, wherein the metal waveguide structure comprises a metal waveguide pattern defining a tapered coupler, preferably a tapered slotted antenna “TSA”, around the tapered end of the dielectric waveguide structure and connected to the first access port (P1) of the ultra-high-speed device.

[0014] The hybrid structure according to the present invention further comprises a low-frequency electrical connection, which can be established by various techniques (e.g., bonding or conductive epoxy), allowing for less restrictive requirements in both spatial and electrical precision. The hybrid structure enables ultra-wideband interconnections of electrical signals between substrates of the same or different permittivity at high frequencies, where a change in the substrate due to the introduction of a discontinuity is critical. High-frequency signal reflections are reduced by bridging the discontinuity, e.g., with conductive epoxy, thereby enabling the signal to be coupled to the dielectric waveguide structure.

[0015] The hybrid structure according to the present invention can further comprise an ultra-high-speed device for which the semiconductor material of the chip is structured to form an RF waveguide that attenuates surface modes and maximizes RF power transfer between the ultra-high-speed device and the metal waveguide structure at their contact surfaces. The semiconductor structure is fabricated during its production by an additional chemical etching (wet etching) process on the substrate of the ultra-high-speed device in a single additional lithography step. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] For better understanding of the above explanation and for the sole purpose of providing an example, some non-restrictive drawings are included which schematically represent a practical embodiment. The Fig. 1 and Fig. Figure 2 shows an embodiment of the prior art. The Fig. 3A to Fig. 3D images show four different embodiments of hybrid structures according to the present invention. The Fig. 4A to Fig. Figure 4D shows the simulated amplitude distribution of the electric field at 10 GHz (a), 60 GHz (b), 140 GHz (c) and 300 GHz (d). The Fig. 5A and Fig. Figure 5B shows the S-parameters obtained from the simulations performed. The Fig. 6A and Fig. Figure 6B shows the intermediate connection of an ultra-high-speed device fabricated on a substrate with high permittivity to another substrate with the same or different permittivity, having a rectangular shape or a shape adapted to the metal pattern. DESCRIPTION OF A PREFERRED VERSION

[0017] Fig. Figure 3A shows an example of an electrical interconnect according to the present invention; in particular, this figure shows an ultra-wideband hybrid structure (100) for high-frequency electrical signals. The structure (100) comprises an ultra-high-speed device on a high-speed semiconductor substrate (105) (for example, but not limited to, indium phosphide “InP”) and a substrate (110), as well as an electrical interconnect (115) provided at the split point between the substrate (110) and the high-speed semiconductor substrate (105). The split point can be selected at a location where the frequency does not cause the hybrid structure (100) to degrade signal transmission in the electrical interconnect.

[0018] The high-speed semiconductor substrate (105) contains the ultra-high-speed device for generating or detecting high-frequency signals (i.e., in the millimeter and terahertz wave range). The electrical contact surfaces of this ultra-high-speed device define an access port (P1) at which an antenna is monolithically defined by its corresponding metallization features. Due to the dimensional limitations of the high-speed semiconductor substrate (105) (i.e., such as indium phosphide), these metallizations are not large enough for the antenna to cover the full frequency range, limiting its operation to above a cutoff frequency. However, because the antenna is monolithically integrated onto the high-speed semiconductor substrate (105), the interface between the ultra-high-speed device and the antenna is optimized to operate at the highest frequencies.As an example, it shows... Fig. 3A an edge-illuminated photomixer device as the ultra-high speed device (i.e. photodiode with waveguide access) illuminated by an optical fiber (130).

[0019] Furthermore, the ultra-wideband hybrid structure (100) includes an optical waveguide (125) between the optical fiber (130) and the waveguide-accessible photodiode when the optical fiber (130) provides optical edge illumination. The substrate (110) is one that allows for larger sizes (e.g., RF substrates such as quartz, laminates, and ceramics, or silicon, among others) on which the larger metallization features corresponding to the TSA antenna or a bifilar metal waveguide can be fabricated. The larger antenna features enable operation over a frequency range that begins at the cutoff frequency of the antenna of the ultra-high-speed device in the high-speed semiconductor substrate (105) and extends to lower frequencies.

[0020] The substrate (110) is located adjacent to the high-speed semiconductor substrate (105) and is compatible with the metallization corresponding to the TSA antenna on each substrate, which is connected by an electrical intermediary (115) such as bonding or conductive epoxy. The electrical intermediary (115) prevents any influence on the performance of the structure (100) at high frequencies, thus providing an effective connection with low insertion losses. This attenuates both reflections and excitation of surface acoustic waves.

[0021] The structure (100) also includes a dielectric waveguide structure (DRW) which includes a second access port (P2) and provides a characteristic high-pass interface operating over a high-frequency range characterized by a low cutoff frequency f CLin the microwave or millimeter wave range. The structure (DRW) is provided on the substrate (110) and on the high-speed semiconductor substrate (105), wherein the structure (DRW) comprises a tapered end that faces or is connected to the access port (P1) of the ultra-high-speed device.

[0022] The structure (100) also includes a bifile metal waveguide structure (TSA) that provides a characteristic low-pass interface that operates over a low frequency range from DC to a high cutoff frequency f CHThe device operates in the millimeter wave range, with the structure (TSA) being provided on the substrate (110) and on the high-speed semiconductor substrate (105). The bifile metal waveguide structure (TSA) is a tapered structure, i.e., it comprises a metal waveguide pattern that defines a tapered coupler, preferably a tapered slotted antenna “TSA”, around the tapered end of the dielectric waveguide structure (DRW) and is located in the near field of the access port (P1) of the ultra-high-speed device.

[0023] The tapered bifilar metal waveguide structure (TSA) is positioned between the high-speed semiconductor substrate (105) and the substrate (110), where the major features of the tapered bifilar metal waveguide are produced. By dividing the tapered bifilar metal waveguide structure (TSA) between both the substrate (110) and the high-speed semiconductor substrate (105), the high frequencies are coupled to the dielectric waveguide (DRW) before reaching the electrical interface (115), e.g., conductive epoxy, between both the substrate (110) and the high-speed semiconductor substrate (105), thus avoiding reflections.

[0024] By appropriately selecting the division point between the substrate (110) and the high-speed semiconductor substrate (105), which each contain complementary parts of the tapered bifilament metal waveguide structure (TSA), the electrical connection between the corresponding metallization of the tapered bifilament metal waveguide structure (TSA) on each substrate (105, 110) does not interfere with the high frequencies already coupled to the dielectric waveguide structure (DRW).

[0025] The structure (100) also includes a second dielectric structure (120), preferably a pyramid-like structure, etched onto the high-speed semiconductor substrate (105). In some examples, the pyramid-like structure is a horn structure that can be provided on either one or both substrates (105, 110) and attenuates the surface waves.

[0026] Therefore, the Fig. 3A to Fig. 3D the intermediate connection of an ultra-high-speed device (electronic or optoelectronic) fabricated on a high-speed semiconductor substrate (105) with another substrate (110), which may have the same or a different permittivity, having an electrical intermediate connection (115), e.g., epoxy, provided between the two substrates (105, 110). The various embodiments of the structure (100) include both horizontal (edge) illumination ( Fig. 3A and Fig. 3C) as well as vertical lighting ( Fig. 3B and Fig. 3D) with an optical fiber (130).

[0027] To attenuate surface modes on the ultra-high-speed device substrate, a second dielectric structure (120), preferably a pyramid-like structure, can be etched onto the high-speed semiconductor substrate (105) ( Fig. 3C and Fig. 3D). This increases the amount of signal coupled in the fundamental mode of the dielectric waveguide (DRW), making it possible to bridge the discontinuity created by bonding substrates with few reflections.

[0028] The Fig. 4A to Fig. 4D shows the simulated amplitude distribution of the electric field at 10 GHz in Fig. 4A, Fig. 60 GHz in Fig. 4B, Fig. 140 GHz in Fig. 4C and Fig. 300 GHz in Fig. 4D for a horizontally illuminated photodiode ( Fig. 4A, Fig. 4C and Fig. 4E), which is made of substrate InP bonded to an aluminum oxide substrate (Al₂O₃, εr = 9.8) (logarithmic amplitude scale). The simulations show how most of the signal travels between the access terminals (P1) and (P2) in a single-mode mode at each frequency. As can be seen, at higher frequencies (Fig. B, C, and D), the signal is coupled from the antenna (TSA) (acting as a near-field coupler) to the tapered end of the silicon (DRW). This coupling occurs close to the photodiode, away from the discontinuity of the substrates (105, 110), thus reducing signal reflections.

[0029] The Fig. 5A and Fig. Figure 5B shows the S-parameters obtained from the simulations performed, which are presented in the Fig. 4A to Fig. 4D are shown. Due to the discontinuity created by the transition between the substrates (105, 110), reflections can occur, as shown in Fig. 5A is shown, although the transmission of signals is possible (assuming a level of -3 dB in S12 and S21) up to at least 340 GHz. To attenuate these reflections, the edge of the high-speed semiconductor substrate (105) to which the ultra-high-speed device is connected can be wound onto the (TSA) ( Fig. 6b). As can be seen in the S parameters, as in Fig. As shown in 5b, the reflections are suppressed, which reduces the degree of ripple in the S parameters.

[0030] Fig. Figure 6A shows another example of an ultra-wideband hybrid structure (100) for high-frequency electrical signals, comprising the interconnection of an ultra-high-speed device for generating or detecting high-frequency signals on a high-speed semiconductor substrate (105) comprising a high permittivity (for example, but not limited to indium phosphide “InP”) and a substrate (110), as well as an electrical interconnection (115) between them.

[0031] In this particular example, the substrate (110) has a rectangular shape that is easier to cut. The substrate (110) is one that allows for larger sizes (i.e., RF substrates such as quartz, laminates, and ceramics, or silicon, among others) on which the larger metallization features corresponding to the TSA antenna or a bifilar metal waveguide can be fabricated.

[0032] Furthermore, it shows Fig. 6A also the ultra-high speed device comprising an edge-illuminated photomixer device (i.e. photodiode with waveguide access) illuminated by an optical fiber (130).

[0033] Due to the discontinuity created by the transition between the substrates (105, 110), reflections can occur, as in Fig. 5A shows. To attenuate these reflections, the edge of the substrate (110) can be wound onto the (TSA). In this respect, it shows Fig. 6B the intermediate connection of an ultra-high speed device fabricated on a substrate with high permittivity to another substrate (110) having a shape adapted or tapered to the metal pattern (TSA). Fig.Figure 6B also shows the ultra-high-speed device comprising an edge-illuminated photomixer device (i.e., a waveguide-accessible photodiode) illuminated by an optical fiber (130) and the second dielectric structure (120), preferably a pyramid-like structure etched onto the high-speed semiconductor substrate (105).

Claims

[1] Ultra-wideband hybrid structure (100) for transmitting or receiving high-frequency electrical signals, wherein the hybrid structure (100) comprises: - a substrate (110); - a high-speed semiconductor substrate (105) connected to the substrate (110); - an electrical intermediate connection (115) provided between the substrate (110) and the high-speed semiconductor substrate (105); - an ultra-high-speed device for generating or detecting high-frequency signals, comprising a first access port (P1) and provided on the high-speed semiconductor substrate (105); - a dielectric waveguide structure (DRW) comprising a second access port (P2) providing a characteristic high-pass interface operating over a high-frequency range characterized by a low cutoff frequency f CLstarting in the microwave or millimeter wave range, wherein the waveguide structure (DRW) is provided on the substrate (110) and on the high-speed semiconductor substrate (105), wherein the waveguide structure (DRW) comprises a tapered end facing the first access port (P1) of the ultra-high-speed device; a metal waveguide structure (TSA) providing a characteristic low-pass intermediate that operates over a low frequency range from DC to a high cutoff frequency f CHoperating in the millimeter wave range, wherein the waveguide structure (TSA) is provided on the substrate (110) and on the high-speed semiconductor substrate (105), wherein the metal waveguide structure (TSA) comprises a metal waveguide pattern defining a tapered coupler, preferably a tapered slotted antenna “TSA”, around the tapered end of the dielectric waveguide structure (DRW) and connected to the first access port (P1) of the ultra-high-speed device. [2] Ultra-wideband hybrid structure (100) according to claim 1, wherein the substrate (110) has a rectangular shape. [3] Ultra-wideband hybrid structure (100) according to claim 1, wherein the substrate (110) has a shape that tapers towards the metal waveguide structure (TSA). [4] Ultra-wideband hybrid structure (100) for high-frequency electrical signals according to one of the preceding claims, further comprising a tapered structure (120) etched onto the high-speed semiconductor substrate (105) and / or the substrate (110). [5] Ultra-wideband hybrid structure (100) for high-frequency electrical signals according to claim 4, wherein the tapered structure (120) is a horn structure. [6] Ultra-wideband hybrid structure (100) for high-frequency electrical signals according to claims 1 to 5, wherein the ultra-high-speed device is an optoelectronic device. [7] Ultra-wideband hybrid structure (100) for high-frequency electrical signals according to claim 6, further comprising: - an optical fiber (130) that provides optical edge illumination or vertical optical illumination for the optoelectronic device. [8] Ultra-wideband hybrid structure (100) for high-frequency electrical signals according to claim 6 or 7, wherein the optoelectronic device is a high-speed photodiode or a photoconductive antenna. [9] Ultra-wideband hybrid structure (100) for high-frequency electrical signals according to claim 8, further comprising: an optical waveguide (125) between the optical fiber (130) and the high-speed photodiode or photoconductive antenna, if the optical fiber (130) provides optical edge illumination. [10] Ultra-wideband hybrid structure (100) for high-frequency electrical signals according to claims 1 to 5, wherein the ultra-high-speed device is an electronic device. [11] Ultra-wideband hybrid structure (100) for high-frequency electrical signals according to any of the preceding claims, wherein the high-speed semiconductor substrate (105) comprises group III-V compound semiconductors such as indium phosphide, gallium nitride, gallium arsenide, InAlAs / InGaAs and / or AlGaN / GaN. [12] Ultra-wideband hybrid structure (100) for high-frequency electrical signals according to any of the preceding claims, wherein the electrical intermediate connection (115) comprises wire bonding, tape bonding, flip-chip bonding or epoxy. [13] Ultra-wideband hybrid structure (100) for high-frequency electrical signals according to one of the preceding claims, wherein the substrate (110) comprises RF substrates such as quartz, laminates, ceramics and / or silicon.

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