Hybrid structures for ultra-wideband terahertz generation and reception using semiconductor devices

Abstract

An ultra-wideband hybrid structure (100) for transmitting high frequency electrical signals, the structure comprising: a substrate (110); a high speed semiconductor substrate (105) connected to the substrate (110) of the ultra-wideband structure (100); a conductive interface (115) constructed between the substrate (110) and the high speed semiconductor substrate (105); an ultra-high speed device defining a first access port (P1) and constructed on the high speed semiconductor substrate (105); and a second access port (P2) and constructed on the substrate (110) and on the high speed semiconductor substrate (105). a dielectric waveguide structure (DRW) having a tapered end connectable to a first access port (P1) of an ultra-high speed device; and a metal waveguide structure (TSA) providing an interconnection with low pass characteristics, the metal waveguide structure (TSA) constructed on a substrate (110) and on a high speed semiconductor substrate (105), the metal waveguide structure (TSA) including a metal waveguide pattern defining a tapered coupler connected to the access port (P1) of a high speed circuit or component.

Description

Detailed Description of the Invention

[0001] [explanation] The present invention relates to a novel structure that allows for the generation and detection of ultra-wideband radio frequency signals by a semiconductor device that has two distinctive features: first, the structure of semiconductor material is shaped to form a radio frequency (RF) waveguide, and second, the structure relies on a hybrid integration of a small die of III-V semiconductor material for the active device that generates the RF and part of the radiating antenna, and a larger silicon material for the remaining part of the antenna and other passive RF components.

[0002] [Background of the invention] Terahertz systems operate in the spectral range covering the frequency band from 0.1 to 10 THz, which lies between the microwave and optical frequency bands. The various technologies for generating and detecting terahertz signals require components integrated on an electronic or photonic die (unpackaged bare chip). Photonic-based systems require an optoelectronic converter, and the active components in the system are the most common ultrafast photodiodes (mainly pin photodiodes, PIN-PDs, and uni-traveling carrier photodiodes, UTC-PDs) and low-temperature grown photoconductive antenna (LTG-PCA) photomixers, which are fabricated using III-V semiconductor composite alloys. There is also a wide range of electronic-based components, commonly Gunn diodes, IMPATT diodes, resonant tunneling diodes (RTDs), and varactor-Schottky diode multipliers, which generate high frequencies as higher harmonics from a microwave reference source.

[0003] The most commonly used semiconductor material substrate for the fabrication of photonic and electronic devices is indium phosphide (InP), a III-V semiconductor compound that has achieved the highest operating frequencies and is therefore a suitable substrate for terahertz systems. However, the main drawbacks of this material are its extreme brittleness and high cost.

[0004] These characteristics have a large impact on the dimensions of the die chip, especially for terahertz generating and receiving devices, where it is desirable to integrate an RF antenna with a larger footprint (millimeter size range) in addition to the components (micrometer size range). The dimensions of the substrate are kept small (0.5 × 0.2 mm) to allow the device to be handled during the assembly process. 2 It cannot be made smaller than the minimum size (greater than 12 mm x 6 mm) and it is not recommended to make it larger than the maximum size (smaller than 12 mm x 6 mm) because the material is fragile. Of course, the chip may have dimensions outside these boundaries, but at the expense of significantly higher assembly costs and lower yields. These limitations also result in systems operating in the lower frequency bands of the spectrum (i.e., in the microwave range from 3 GHz to 30 GHz, or the millimeter wave range from 30 GHz to 300 GHz) where the die chip area is not sufficient to monolithically integrate the antenna on the substrate used for the component.

[0005] One current approach for assembling the chip die and antenna is shown in Figure 1, which depicts a 3D model of the assembly (50) that includes an optical fiber aligned with the optical input of an ultrafast photodiode (PD chip). The electrical contact pad of the ultrafast photodiode excites a planar tapered slot antenna (TSA) through a microwave access port (excitation port 1). Specifically, Figure 1 shows the InP (ε r =12.4) on a 110RT / Duroid5880 low-k substrate (ε r Figure 2 shows a high-speed photodiode device connected to a TSA-type antenna fabricated on a GaN- ...

[0006] Among the various interconnect technologies currently available, the most common in the electronics industry is gold wire bonding. Figure 2 shows a photograph of an InP integrated ultrafast photodiode chip (200), whose electrical contact pads are connected to the access port of an antenna via gold wire bonds. However, the series parasitic inductance of the gold wires implies a limit to the maximum operating frequency, although this is partially suppressed by using two bond wires per connection.

[0007] A further difficulty in the interconnection between the component die chip and the antenna RF substrate is the difference in dielectric constant between the substrates. The die chip, which has a relatively high refractive index, creates reflections at this interface, which are particularly detrimental to high-frequency signals. These reflections mean that part of the signal returns to the transmitting device, which reduces the efficiency of the transmitting module.

[0008] The present invention overcomes the aforementioned limitations and drawbacks.

[0009] [Description of the Invention] The present invention provides a solution to exploit the full bandwidth of ultra-wideband antennas driven by ultrafast semiconductor devices, allowing different substrates to be combined, and overcoming the current constraints of available electrical interconnects that limit the bandwidth of terahertz and sub-terahertz systems.

[0010] Thus, the present invention presents a new structure for ultra-high speed devices based on hybrid dielectric conductor guides that operate from direct current (DC) to at least 300 GHz. The present invention proposes an ultra-wideband hybrid structure optimized for high frequency electrical signals that can operate up to 340 GHz and can be designed to reach higher frequencies by varying the thickness and / or dielectric constant of the substrate. The ultra-wideband structure allows the coupling of high frequency signals from high speed circuits or components fabricated on high speed semiconductor substrates (e.g. indium phosphide). For technical, manufacturing or handling reasons, the dimensions of high speed semiconductor substrates may be limited (i.e., they are dimensionally constrained, preventing the integration of wideband waveguides such as tapered bifilar metallic waveguides or large components such as antennas). The ultra-wideband structure solves this problem and allows high performance radiation of high frequency signals. Thus, as shown in Figures 4A-4D, the ultra-wideband structure according to the present invention allows the coupling of the majority of signals into a single mode for all frequencies within the operating bandwidth.

[0011] The main aspects of the hybrid structure according to the present invention are as follows: A dielectric waveguide excited in a single mode manner that provides coupling of signals to and from the component die chip at high frequencies. This dielectric waveguide structure has a high-pass filter characteristic and a low cutoff frequency (f CL ) to enable the electrical interconnection of signals with frequencies above 100 GHz. A dielectric waveguide with a tapered end facing the access port (P1) of an ultrafast semiconductor device (electronic or optoelectronic device) fabricated on a high dielectric constant substrate (e.g., indium phosphide) cut into a die chip. For example, the dielectric waveguide structure can be used for low cutoff frequencies (f CL), starting at an operating frequency of, for example, 60 GHz, and can be designed to operate over a wide frequency range, for example, spanning the terahertz wave range (i.e., 300-3000 GHz) and beyond. A dielectric waveguide structure can be constructed on the substrate (110) and on the high speed semiconductor substrate, with the structure having a tapered end facing the first access port of the ultrafast device.

[0012] The hybrid structure according to the present invention also includes a metal waveguide structure with low pass filter characteristics, which allows for establishing metallic electrical contact with the access ports of ultrafast devices, and allows the operating frequency range of the interconnection to start at low frequencies (i.e., preferably DC, 0 Hz), thereby allowing for high cutoff frequencies (f CH ) allows electrical interconnection of signals up to 100 Hz. For example, the metal waveguide structure can be designed to operate at frequencies starting at 0 Hz and up to the millimeter wave range (i.e., between 30 GHz and 300 GHz, e.g., 100 GHz operating frequency). In a preferred embodiment for broadband operation, the metal waveguide structure starts at low frequencies (i.e., at DC or starting at 0 Hz) and exceeds the low cutoff frequency (f) of the dielectric waveguide structure. CH >f CL , e.g., above 60 GHz in the previous example).

[0013] A metal waveguide structure can be constructed on the substrate and on the high speed semiconductor substrate, the metal waveguide structure including a metal waveguide pattern around the tapered end of the dielectric waveguide structure that defines a tapered coupler, preferably a tapered slot antenna "TSA", that is connected to a first access port (P1) of the ultrahigh speed device.

[0014] The hybrid structure of the present invention further includes electrical connections at low frequencies that can be realized by various techniques (e.g., bonding or conductive epoxy) that allow less restrictive requirements in both spatial and electrical precision. The hybrid structure allows ultra-wideband interconnection of electrical signals at high frequencies between substrates with the same or different dielectric constants. In ultra-wideband interconnection, substrate changes are critical because they introduce discontinuities. Reflections of high frequency signals are reduced by filling the discontinuities, for example by allowing the signal to be coupled to a dielectric waveguide structure with conductive epoxy.

[0015] The hybrid structure of the present invention may further include an ultrafast device in which the semiconductor material of the chip die is structured in the shape of an RF waveguide that suppresses surface modes and maximizes RF power transfer between the ultrafast device and a metal waveguide structure at its contact pad, the semiconductor structure being fabricated by additional processing of chemical etching (wet etching) into the substrate of the ultrafast device in a single additional lithography step during the fabrication of the substrate of the ultrafast device. [Brief description of the drawings]

[0016] For a better understanding of the above description and for the purpose of example only, some non-limiting drawings are included which show, in a schematic manner, practical embodiments. [Figure 1] 1 shows an embodiment of the prior art. [Diagram 2] 1 shows an embodiment of the prior art. [Figure 3A] 1 shows four different embodiments of a hybrid structure according to the invention. [Figure 3B] 1 shows four different embodiments of a hybrid structure according to the invention. [Figure 3C] 1 shows four different embodiments of a hybrid structure according to the invention. [Figure 3D] 1 shows four different embodiments of a hybrid structure according to the invention. [Figure 4A] The simulated electric field amplitude distribution at 10 GHz (a) is shown. [Figure 4B] The simulated electric field amplitude distribution at 60 GHz (b) is shown. [Figure 4C] The simulated electric field amplitude distribution at 140 GHz (c) is shown. [Figure 4D] The simulated electric field amplitude distribution at 300 GHz (d) is shown. [Figure 5A] The S-parameters obtained from the performed simulation are shown. [Figure 5B] The S-parameters obtained from the performed simulation are shown. [Figure 6A] The interconnection of ultra-high speed devices fabricated on a high dielectric constant substrate with another substrate having the same or different dielectric constant and having a rectangular shape or a shape that conforms to a metal pattern is shown. [Figure 6B] The interconnection of ultra-high speed devices fabricated on a high dielectric constant substrate with another substrate having the same or different dielectric constant and having a rectangular shape or a shape that conforms to a metal pattern is shown. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Description of the Preferred Embodiments FIG. 3A shows an example of an electrical interconnect according to the present invention. Specifically, the figure shows an ultra-wideband hybrid structure (100) for high frequency electrical signals. The structure (100) includes an ultra-high speed device on a high speed semiconductor substrate (105) (e.g., but not limited to, indium phosphide "InP") and a substrate (110), and an electrical interconnect (115) built at a split point between the substrate (110) and the high speed semiconductor substrate (105). The split point can be selected at a location in the electrical interconnect where the frequency does not cause degradation of signal transmission through the hybrid structure (100).

[0018] The high-speed semiconductor substrate (105) contains an ultrafast device for generating or detecting high-frequency signals (mm-wave and terahertz range). The electrical contact pads of this ultrafast device define an access port (P1) where an antenna is monolithically defined through corresponding metallization features. Due to the limitations of the dimensions of the high-speed semiconductor substrate (105) (i.e., indium phosphide, etc.), these metallizations do not have the size required for the antenna to cover the full frequency range and are limited to operate at frequencies higher than the cutoff frequency. However, since the antenna is monolithically integrated on the high-speed semiconductor substrate (105), the interface between the ultrafast device and the antenna is optimized to operate at the highest frequency. As an example, FIG. 3A shows an edge-illuminated photomixer arrangement as an ultrafast device (i.e., a waveguide-accessed photodiode) illuminated via an optical fiber (130).

[0019] Additionally, the ultra-wideband hybrid structure (100) includes an optical waveguide (125) between the optical fiber (130) and the waveguide-access photodiode, where the optical fiber (130) provides edge-light illumination. The substrate (110) allows for a larger size (e.g., RF substrates such as quartz, laminate, ceramic, or silicon) on which larger metallization features corresponding to the TSA antenna or bifilar metal waveguide can be built. The larger features of the antenna allow operation over a frequency range starting from the cutoff frequency of the antenna of the ultra-high speed device in the high speed semiconductor substrate (105) and extending towards lower frequencies.

[0020] The substrate (110) is located next to the high speed semiconductor substrate (105) and is mated with metallization corresponding to the TSA antenna on each substrate. The TSA antennas on each substrate are interconnected by electrical interconnects (115), such as bonding or conductive epoxy. The electrical interconnects (115) avoid affecting the performance of the structure (100) at high frequencies and provide an effective connection with low insertion loss. Thus, both reflection and excitation of surface waves are suppressed.

[0021] The structure (100) includes a second access port (P2) and is adapted to receive a low cutoff frequency f in the microwave or millimeter wave range. CL Also included is a dielectric waveguide structure (DRW) that provides an interconnect with high-pass characteristics operating over a high frequency range beginning at 100 MHz. The structure (DRW) is constructed on the substrate (110) and on the high speed semiconductor substrate (105) and has a tapered end facing or connected to an access port (P1) of the ultra-high speed device.

[0022] The structure (100) provides an interconnect with low-pass characteristics and a high cutoff frequency f in the DC to mm-wave range. CH The bifilar metal waveguide structure (TSA) also includes a bifilar metal waveguide structure (TSA) operating over a low frequency range up to 100 MHz. The structure (TSA) is constructed on the substrate (110) and on the high-speed semiconductor substrate (105). The bifilar metal waveguide structure (TSA) is a tapered structure. That is, the bifilar metal waveguide structure (TSA) includes a metal waveguide pattern that defines a tapered coupler, preferably a tapered slot antenna "TSA", around the tapered end of the dielectric waveguide structure (DRW) and is placed in the near field of the access port (P1) of the ultra-high speed device.

[0023] A tapered bifilar metal waveguide structure (TSA) is constructed between the high speed semiconductor substrate (105) and the substrate (110) to fabricate larger features of the tapered bifilar metal waveguide. By splitting the tapered bifilar metal waveguide structure (TSA) between the two, the substrate (110) and the high speed semiconductor substrate (105), the high frequency is coupled into the dielectric waveguide (DRW) before reaching the electrical interconnect (115), for example, via the conductive epoxy between the two, the substrate (110) and the high speed semiconductor substrate (105), thereby avoiding reflections.

[0024] By appropriately selecting the division point between the substrate (110) and the high speed semiconductor substrate (105), each of which contains a complementary portion of the tapered bifilar metal waveguide structure (TSA), the electrical interconnection between the corresponding metallizations of the tapered bifilar metal waveguide structure (TSA) on each substrate (105, 110) does not disturb the high frequencies already coupled to the dielectric waveguide structure (DRW).

[0025] The structure (100) also includes a second dielectric structure (120), preferably a pyramidal structure, etched onto the high speed semiconductor substrate (105). In some examples, the pyramidal structure may be constructed on one or both of the substrates (105, 110) and is a horn structure that suppresses surface waves.

[0026] Thus, Figures 3A-3D show the interconnection of ultrafast devices (electronic or optoelectronic) fabricated on a high speed semiconductor substrate (105) with another substrate (110) that may have the same or different dielectric constant. The interconnect has an electrical interconnect (115), e.g., epoxy, constructed between both substrates (105, 110). Different embodiments of the structure (100) provide both horizontal (edge) illumination (Figures 3A and 3C) and vertical (Figures 3B and 3D) illumination by optical fibers (130).

[0027] To suppress surface modes on the ultrafast device substrate, a second dielectric structure (120), preferably a pyramidal structure, may be etched onto the high speed semiconductor substrate (105) (Figures 3C and 3D), which increases the amount of signal coupled into the fundamental mode of the dielectric waveguide (DRW) and allows bridging the discontinuity caused by the substrate bond to produce almost no reflection.

[0028] Figures 4A-4D show simulated electric field amplitude distributions at 10 GHz (Figure 4A), 60 GHz (Figure 4Bb), 140 GHz (Figure 4C), and 300 GHz (Figure 4D) for a horizontally illuminated photodiode (Figures 4A, 4C, 4E) made of InP substrate bonded to an alumina substrate (Al2O3, εr=9.8) (logarithmic amplitude scale). The simulations show that at each frequency, the majority of the signal travels single-mode between the access ports (P1) and (P2). As can be seen, at higher frequencies (Figures B, C, 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 and away from discontinuities in the substrate (105, 110), thus reducing signal reflections.

[0029] Figures 5A and 5B show the S-parameters obtained from the performed simulations shown in Figures 4A-4D. Although the discontinuities created by the transition between the substrates (105, 110) can cause reflections as shown in Figure 5A, the transmission of signals is possible up to at least 340 GHz (assuming S12 and S21 levels of -3 dB). To suppress these reflections, the end face of the high-speed semiconductor substrate (105) to which the ultra-high-speed devices are connected can be wrapped on a (TSA) (Figure 6b). As can be seen from the S-parameters shown in Figure 5b, the reflections are suppressed and the ripple level of the S-parameters is reduced.

[0030] FIG. 6A shows another example of an ultra-wideband hybrid structure (100) for high frequency electrical signals, including a high speed semiconductor substrate (105) with a high dielectric constant (such as, but not limited to, indium phosphide "InP") and interconnections of ultra-high speed devices for generating or detecting high frequency signals on the substrate (110), as well as electrical interconnections (115) therebetween.

[0031] In this embodiment, the substrate (110) has a rectangular shape that is easy to cut, and the substrate (110) allows for larger sizes (i.e., RF substrates such as quartz, laminates, ceramics, or silicon, etc.) on which larger metallization features corresponding to TSA antennas or bifilar metal waveguides can be built.

[0032] Additionally, FIG. 6A also shows an ultrafast device comprising an edge-illuminated photomixer arrangement (ie, a waveguide-accessed photodiode) illuminated via an optical fiber (130). Discontinuities caused by the transition between the substrates (105, 110) can cause reflections as shown in FIG. 5A. To suppress these reflections, the end face of the substrate (110) can be wrapped onto a (TSA). In this regard, FIG. 6B shows an interconnection between an ultrafast device fabricated or built on a high dielectric constant substrate and another substrate (110) that matches or has a tapered shape with a metal pattern (TSA). FIG. 6B also shows an ultrafast device comprising an edge-illuminated photomixer device (i.e., a waveguide-accessed photodiode) illuminated via an optical fiber (130) and a second dielectric structure (120), which is preferably a pyramidal structure etched on the high speed semiconductor substrate (105).

Claims

1. 1. An ultra-wideband hybrid structure for transmitting or receiving high frequency electrical signals, said ultra-wideband hybrid structure comprising: A substrate; a high speed semiconductor substrate connected to the substrate; an electrical interconnection established between the substrate and the high speed semiconductor substrate; an ultra-high speed device for generating or detecting high frequency signals, the ultra-high speed device having a first access port and constructed on the high speed semiconductor substrate; A second access port is provided, and a low cutoff frequency f ＣＬ a dielectric waveguide structure providing an interconnection with high-pass characteristics operating in a high frequency region starting from Provides interconnects with low-pass characteristics, and high cutoff frequencies f from DC to millimeter-wave range. ＣＨ a metal waveguide structure operating in a low frequency range up to 100 MHz, constructed on the substrate and on the high-speed semiconductor substrate, the metal waveguide structure comprising a metal waveguide pattern around a tapered end of the dielectric waveguide structure defining a tapered coupler connected to the first access port of the ultrahigh-speed device; An ultra-wideband hybrid structure.

2. The tapered coupler is a tapered slot antenna. The ultra-wideband hybrid structure of claim 1 .

3. The substrate is rectangular.

3. The ultra-wideband hybrid structure according to claim 1 or 2.

4. the substrate has a tapered shape with respect to the metal waveguide structure; 3. The ultra-wideband hybrid structure according to claim 1 or 2.

5. further comprising a tapered structure etched on the high speed semiconductor substrate and / or the substrate; 3. The ultra-wideband hybrid structure according to claim 1 or 2.

6. The tapered structure is a horn structure.

6. The ultra-wideband hybrid structure of claim 5.

7. The ultrafast device is an optoelectronic device.

3. The ultra-wideband hybrid structure according to claim 1 or 2.

8. The optoelectronic device is a high-speed photodiode or a photoconductive antenna.

8. The ultra-wideband hybrid structure of claim 7.

9. The optoelectronic device according to claim 8, wherein the optoelectronic device is a high-speed photodiode. Further, an optical fiber is provided to irradiate the high-speed photodiode with edge light or vertical light.

9. The ultra-wideband hybrid structure of claim 8.

10. When the optical fiber irradiates an end face light, an optical waveguide is further provided between the optical fiber and the high-speed photodiode.

10. The ultra-wideband hybrid structure of claim 9.

11. The ultrafast device is an electronic device.

3. The ultra-wideband hybrid structure according to claim 1 or 2.

12. The high-speed semiconductor substrate comprises a III-V group compound semiconductor of indium phosphide, gallium nitride, gallium arsenide, InAlAs / InGaAs, or AlGaN / GaN; 3. The ultra-wideband hybrid structure according to claim 1 or 2.

13. the electrical interconnects comprise wire bonding, ribbon bonding, flip chip bonding, or epoxy; 3. The ultra-wideband hybrid structure according to claim 1 or 2.

14. the substrate comprises quartz, laminate, and ceramic RF substrate, or silicon; 3. The ultra-wideband hybrid structure according to claim 1 or 2.

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