A photonic antenna operating at 275 - 296 GHz

Abstract

The present invention discloses a photonic antenna operating at 275 - 296 GHz, belonging to the fields of optoelectronics and terahertz communication; it includes two UTC-PD bodies and a passive structure; the UTC-PD body adopts a double mesa structure, and each structure leads out electrodes through electroplated small pads, and metal bumps are processed on the small pads to generate electrical connection with the passive structure through flip-chip bonding. The passive structure includes an impedance matching circuit, a power combiner circuit, and a Vivaldi antenna; the UTC-PD body generates signals, and a built-in electric field is introduced by using a gradient-doped absorption layer; a cliff layer is provided between the absorption layer and the collection layer; then, after the signal passes through the impedance matching circuit and the output impedance is close to 50 ohms, the two combined output signals are superimposed on the feed end of the Vivaldi antenna through the power combiner, and finally, it is converted into high-frequency electromagnetic waves in the 275 - 296 GHz frequency band for radiation. The present invention generates and emits electromagnetic waves in the terahertz frequency range, achieving technical performances of high bandwidth, high gain, and low insertion loss.

Description

Technical Field

[0001] The present invention belongs to the field of optoelectronics and terahertz communication, and relates to a photonic antenna operating at 275 - 296 GHz. Background Art

[0002] Terahertz (THz) technology has broad prospects in fields such as broadband wireless communication, spectroscopic analysis, security imaging, and biomedical diagnosis due to its unique frequency range (0.1 - 10 THz). Compared with traditional optical and microwave technologies, terahertz waves have advantages such as strong penetrability, moderate wavelength, and non - ionization, and can achieve unique functions in high - resolution imaging and precise spectral recognition. Therefore, it is known as the "core frequency band of future technology".

[0003] In the terahertz band, traditional transistor technology is difficult to meet the high - frequency requirements. Especially above 100 GHz, the cut - off frequency and power gain of transistors decay rapidly. Therefore, photodetectors have become key components and need to have characteristics such as high speed, high responsivity, and high saturation output.

[0004] Due to the limitation of the space - charge effect, traditional PIN photodetectors are difficult to meet the requirements of high bandwidth and high - power output. While uni - traveling - carrier photodetectors (UTC - PDs) through optimized design make full use of electrons as the only carriers, and their photodetection performance has been significantly improved in terms of bandwidth and response speed.

[0005] Relying on the characteristics of high speed, high response, and weak space - charge effect, UTC - PDs have become a research hotspot in the field of optoelectronic devices. However, the traditional UTC - PD design still has bottlenecks in terms of integration, impedance - matching efficiency, and power - output consistency, which hinders its wide application in higher frequency bands (such as 275 - 296 GHz). Summary of the Invention

[0006] The present invention proposes a photonic antenna operating at 275 - 296 GHz, which adopts a monolithic integrated design. By optimizing the impedance - matching circuit, integrating an efficient power combiner, and innovatively designing a broadband antenna, the efficient generation and transmission of signals in the terahertz band are achieved. Combining the performance advantages of photodetectors with the advanced process of integrated circuits, the present invention provides a new solution for 275 - 296 GHz terahertz communication and related applications.

[0007] The photonic antenna operating at 275 - 296 GHz includes a UTC - PD body and a passive structure; the passive structure includes an impedance - matching circuit, a power - combiner circuit, and a Vivaldi antenna;

[0008] There are two UTC-PD bodies in total. Each UTC-PD body adopts a double mesa structure. The two identical structures both lead out electrodes through electroplated small pads. Metal bumps are processed on each small pad, and electrical connections are made with the passive structures processed on the quartz substrate through flip-chip bonding.

[0009] The epitaxial structure of the UTC-PD body from top to bottom is: P-type ohmic contact layer, blocking layer, absorption layer and collection layer.

[0010] The blocking layer includes a P-type blocking layer InP and a P-type blocking layer InGaAsP;

[0011] The absorption layer includes a P-type heavily doped non-depleted absorption layer InGaAs and a P-type doped depleted absorption layer InGaAs; The absorption layer introduces a built-in electric field in a gradient doping manner. The concentration difference brings about a potential difference, introducing a high electric field to accelerate electrons through the absorption layer;

[0012] The collection layer includes an N-type doped cliff layer InP and an N-type lightly doped collection layer InP; The presence of the cliff layer InP increases the electric field of the absorption layer while reducing the electric field of the collection layer.

[0013] The two UTC-PD bodies require two completely symmetric impedance matching circuits. In the frequency range of 275 - 296 GHz, the output impedance of the UTC-PD is adjusted to be close to 50 Ω to optimize the power transmission efficiency in this frequency band and minimize the reflection loss.

[0014] The impedance matching circuit is processed on a quartz substrate with a relative dielectric constant of 3.78 and consists of a series transmission line, a short-circuited stub and a MIM capacitor. Among them, both the series transmission line and the short-circuited stub exist in the form of a coplanar waveguide;

[0015] The output impedance of the UTC-PD is adjusted to be close to 50 ohms, and the specific calculation formula is:

[0016] First, the output impedance of the UTC-PD body in a certain frequency band is: Z = m + j*n;

[0017] Where m is the resistance and n is the reactance;

[0018] Then, the impedance of the impedance matching circuit Z1 = a + j*c;

[0019] Where a is the resistance and c is the reactance;

[0020] Finally, calculate the impedance matching: that is, the impedance Z and Z1 satisfy: Z + Z1 = 50 + j*0, that is, the output resistance of the UTC-PD with the impedance matching circuit superimposed is 50 ohms and the reactance is zero in this frequency band.

[0021] After the impedance matching circuit, a T-junction power combiner is used to superimpose the two signals after impedance matching. The two input terminals of the power combiner respectively correspond to the output terminals of the two impedance matching circuits.

[0022] The T-junction power combiner consists of an input terminal with a length of 10um and a characteristic impedance of 50 ohms; a quarter-wavelength impedance transformation section with a length of 177um and a characteristic impedance of 70.7 ohms; and an output terminal with a length of 30um and a characteristic impedance of 50 ohms.

[0023] After the output port of the power combiner, a Vivaldi antenna is connected. This antenna is fed by a coplanar waveguide, directly radiates the terahertz signal into free space, and maintains a relatively high gain.

[0024] The Vivaldi antenna consists of a feeding end, a radiation structure, and a reflection structure;

[0025] The feeding end adopts a coplanar waveguide structure, which is exactly the same as the structure of the third port of the T-junction power combiner.

[0026] The radiation structure consists of an exponentially varying open structure. To improve the gain, slots are cut on the radiation patch of the antenna, and a metal block is added in the middle of the dielectric substrate for guiding. To reduce the gain of the back lobe and side lobes, an arc-shaped reflection structure is designed on the back of the dielectric substrate.

[0027] Furthermore, the width of each slot is 30um, the slot pitch is 100um, and the height of the slot decreases in units of 50um starting from 200um.

[0028] The photon antenna operating at 275 - 296 GHz has the following working principle:

[0029] The UTC-PD body of this photon antenna generates a signal. The built-in electric field is introduced by the gradient-doped absorption layer to accelerate the movement of electrons in the absorption layer; the cliff layer between the absorption layer and the collection layer enhances the electric field in the absorption layer while reducing the electric field in the collection layer; then, after the signal passes through the impedance matching circuit to ensure that the output impedance of the UTC-PD is close to 50 ohms in the frequency range of 275 - 296 GHz, the output signals of the two UTC-PD signal sources combined with the impedance matching circuit are superimposed on the feeding end of the Vivaldi antenna through the power combiner. Finally, it is converted into high-frequency electromagnetic waves in the 275 - 296 GHz frequency band for radiation.

[0030] The advantages of the present invention are as follows:

[0031] (1) A photonic antenna operating at 275 - 296 GHz adjusts the load impedance of the UTC-PD to be close to 50 ohms within the frequency range of 275 - 296 GHz through an impedance matching circuit, optimizing the power transfer efficiency in this frequency band and minimizing the reflection loss.

[0032] (2) A photonic antenna operating at 275 - 296 GHz uses a T-junction power combiner to superimpose two impedance-matched signals and maintains a relatively low reflection coefficient at the resonant frequency.

[0033] (3) A photonic antenna operating at 275 - 296 GHz is connected with a Vivaldi antenna after the power combiner. This antenna can directly radiate terahertz signals into free space and maintain a relatively high gain.

[0034] (4) A photonic antenna operating at 275 - 296 GHz integrates two UTC-PDs with a P mesa diameter of 3 um and small pads directly with the passive structure on a quartz substrate through flip-chip bonding. Processing the passive structure on the quartz substrate instead of the InP wafer can improve the utilization rate of the InP wafer; at the same time, the active device UTC-PD and the passive structure can be optimized separately, reducing the experimental cost. Description of the Drawings

[0035] Figure 1 This is a three-dimensional structure diagram of a photonic antenna operating at 275 - 296 GHz according to the present invention;

[0036] Figure 2 This is a top view of a photonic antenna operating at 275 - 296 GHz according to the present invention;

[0037] Figure 3 This is a schematic diagram of the impedance matching circuit and the power combiner module used in the present invention;

[0038] Figure 4 This is a schematic diagram of the Vivaldi antenna used in the present invention;

[0039] Figure 5 This is a schematic diagram of the back reflection structure of the Vivaldi antenna in the present invention;

[0040] Figure 6 This is a schematic diagram of the curve of the reflection coefficient varying with frequency after the power combining circuit, the front-end impedance matching circuit and the UTC-PD are integrated in the present invention;

[0041] Figure 7 This is the E-plane pattern and the 3D pattern of the Vivaldi antenna in the present invention;

[0042] Figure 8The E-plane pattern and 3D pattern of the photon antenna of the present invention;

[0043] Figure 9 Schematic diagram of the gain variation curve of the photon antenna of the present invention with frequency.

[0044] In the figure: ① is the UTC-PD body, ② is the impedance matching circuit, ③ is the power combiner, and ④ is the Vivaldi antenna. Detailed implementation mode

[0045] The present invention will be further described in detail below in conjunction with the drawings and embodiments.

[0046] The present invention relates to a photon antenna operating in the 275-296 GHz frequency band. By means of a monolithic integration process, an ultrafast photodetector (UTC-PD), an impedance matching circuit, a power combiner, and a Vivaldi antenna are combined together to generate and emit electromagnetic waves in the terahertz frequency range, thereby achieving technical performances of high bandwidth, high gain, and low insertion loss. The present invention significantly improves the generation and transmission efficiency of terahertz signals in the 275-296 GHz range, has the advantages of high integration, stable performance, and strong reliability, and has the significance of promoting the development of terahertz communication technology and expanding its applications in fields such as high-speed communication, precision measurement, and biomedicine.

[0047] The photon antenna operating in the 275-296 GHz range, as Figure 1 and Figure 2 shown, includes four parts: a UTC-PD body, an impedance matching circuit, a power combiner circuit, and a Vivaldi antenna;

[0048] There are two UTC-PD bodies in total. Each UTC-PD body adopts a double mesa structure. The diameter of the P mesa is 3 μm. Its epitaxy from top to bottom is: P-type ohmic contact layer, blocking layer, absorption layer, and collection layer;

[0049] The blocking layer includes a P-type blocking layer InP and a P-type blocking layer InGaAsP;

[0050] The absorption layer includes a P-type heavily doped non-depleted absorption layer InGaAs and a P-type doped depleted absorption layer InGaAs; the absorption layer introduces an internal built-in electric field by means of gradient doping. The concentration difference brings about a potential difference, introducing a high electric field to accelerate electrons through the absorption layer; According to Poisson's Equation: where is the electric potential, ρ is the charge density, and ε is the dielectric constant. Thus, it can be seen that the gradient change of the doping concentration will affect the charge density, thereby generating a potential difference.

[0051] The collection layer includes an N-type doped cliff layer InP and an N-type lightly doped collection layer InP; the presence of the cliff layer InP changes the internal electric field distribution of the device, extends the electric field towards the absorption region, and results in a lower electric field in the collection region than without the cliff layer. This is because when a fixed reverse bias voltage is applied to the UTC-PD, if the electric field strength in a certain part of the UTC-PD increases, then other parts will necessarily decrease; thus, while increasing the electric field in the absorption layer, the electric field in the collection layer is reduced.

[0052] The epitaxial structures of the two UTC-PD bodies are the same. Electroplated small pads are used to lead out the electrodes through two simultaneous processes. Metal bumps are processed on each small pad, and electrical connections are made with the passive structures processed on the quartz substrate through flip-chip bonding. The passive structures include an impedance matching circuit, a power combiner, and a Vivaldi antenna.

[0053] Two UTC-PDs require two completely symmetric impedance matching structures. Through the impedance matching circuit, in the frequency range of 275 - 296 GHz, the output impedance of the UTC-PD is adjusted to be close to 50 Ω, optimizing the power transfer efficiency in this frequency band and minimizing the reflection loss; the specific calculation formula is:

[0054] The output impedance of the UTC-PD in a certain frequency band is: Z = m + j*n; where m is the resistance and n is the reactance; the unit is ohm. Then, the impedance of the impedance matching circuit Z1 = a + j*c; where a is the resistance and c is the reactance;

[0055] Finally, the impedance matching is calculated: that is, the impedance Z and Z1 satisfy: Z + Z1 = 50 + j*0, which means that the output resistance of the UTC-PD with the impedance matching circuit superimposed in this frequency band is 50 ohms and the reactance is zero.

[0056] Although the use of an impedance matching circuit can increase the output power of the UTC-PD in this frequency band, the improvement effect is limited. Therefore, a T-junction power combiner is used after the impedance matching circuit to superimpose the two impedance-matched signals. The two input ports of the power combiner correspond to the output ports of the two impedance matching circuits respectively, as Figure 3 shown; where L1 is the length of the series transmission line in the impedance matching circuit, L2 is the length of the short-circuited stub in the impedance matching circuit, and L3 and L4 belong to the impedance transformation part of the power combiner, and the sum of the two is close to a quarter wavelength.

[0057] A Vivaldi antenna is connected after the output port 3 of the power combiner. This antenna is fed by a coplanar waveguide, directly radiates the terahertz signal into free space, and maintains a high gain. The antenna structure is as Figure 4 shown, L is the length of the radiation structure, and W is the opening width of the radiation structure.

[0058] The impedance matching circuit is fabricated on a quartz substrate with a relative dielectric constant of 3.78 and consists of a series transmission line, a short - circuited stub, and a MIM capacitor. Among them, both the series transmission line and the short - circuited stub exist in the form of a coplanar waveguide with a characteristic impedance of 50 ohms, and the dielectric layer of the MIM capacitor is SiNx.

[0059] The T - junction power combiner consists of an input end with a length of 10 um and a characteristic impedance of 50 ohms, a quarter - wavelength impedance transformation section with a length of 177 um and a characteristic impedance of 70.7 ohms, and an output end with a length of 30 um and a characteristic impedance of 50 ohms.

[0060] The Vivaldi antenna consists of a feeding end, a radiation structure, and a reflection structure. The feeding end adopts a coplanar waveguide structure, which is exactly the same as the structure of the third port of the T - junction power combiner. The radiation structure consists of an exponentially varying open - ended structure. To improve the gain, slots are cut on the radiation patch of the antenna, and metal blocks are added in the middle of the dielectric substrate for guiding. To reduce the gain of the back lobe and side lobes, an arc - shaped reflection structure is designed on the back of the dielectric substrate, and the reflection structure is as Figure 5 shown.

[0061] The slots are located on the radiation arms. The width of each slot is 30 um, the slot pitch is 100 um, and the height of the slots starts from 200 um and decreases in units of 50 um.

[0062] The photon antenna operating at 275 - 296 GHz has the following working principle:

[0063] The UTC - PD body of the photon antenna generates signals. By using a gradient - doped absorption layer to introduce an internal built - in electric field, the movement of electrons in the absorption layer is accelerated, improving the photoelectric conversion efficiency. The cliff layer between the absorption layer and the collection layer enhances the electric field in the absorption layer while reducing the electric field in the collection layer, optimizing the flow of carriers and reducing energy loss. Then, after the signal passes through the impedance matching circuit to ensure that the output impedance of the UTC - PD is close to 50 ohms within the frequency range of 275 - 296 GHz, maximum power transmission is achieved and reflection loss is reduced. Next, through the power combiner, the output signals of two UTC - PD signal sources combined with the impedance matching circuit are superimposed on the feeding end of the Vivaldi antenna, enhancing the output power of the system. Finally, the signal is converted into high - frequency electromagnetic waves in the 275 - 296 GHz frequency band through the Vivaldi antenna for radiation, achieving efficient signal transmission. This design is applicable to applications such as high - frequency communication and radar detection, improving the system performance and signal transmission efficiency.

[0064] Embodiment:

[0065] This invention uses HFSS for electromagnetic simulation. The simulation environment includes a substrate model based on quartz (relative dielectric constant is 3.78) and a circuit matching structure, and the operating frequency band is 275 - 296 GHz. The specific steps are as follows:

[0066] Step 1: The UTC - PD adopts a double - mesa structure. The diameter of the P - mesa is 3μm, which effectively optimizes the RC time constant and improves the electron migration speed. Under a reverse bias of 3V, the electric field in the depletion region of the device is 20 - 40 kV / cm, and the electron transit - time bandwidth can reach 325 GHz.

[0067] Step 2: The impedance - matching circuit includes a series transmission line, a short - circuited stub, and a MIM capacitor.

[0068] Among them, the length L1 of the series transmission line is 75μm, the length L2 of the short - circuited stub is 43μm. Both the series transmission line and the stub adopt the form of coplanar waveguide, and the characteristic impedance is 50 ohms; the dielectric layer of the MIM capacitor is SiNx with a thickness of 0.2μm.

[0069] Step 3: The T - type power combiner consists of an input end, a quarter - wavelength impedance - transformation section, and an output end.

[0070] The length of the impedance - transformation part is the sum of L3 and L4, equal to 177μm. After integrating this power - combining circuit with the front - end impedance - matching circuit and UTC - PD, it resonates at 285 GHz, and the reflection coefficient is lower than - 39 dB, as Figure 6 shown, and it can effectively integrate the signals of two UTC - PDs after impedance matching.

[0071] Step 4: The length L of the Vivaldi antenna radiation structure is 1.1 mm, the opening width W at the end is 0.65 mm, and the thickness of the metal layer is 2μm. Through optimization, the back - lobe gain of the antenna is reduced to - 1.9 dBi, and the gain of the antenna in the radiation direction reaches 8.9 dBi. The E - plane pattern and 3D pattern are as Figure 7 shown.

[0072] Step 5: Two UTC - PDs with the same epitaxial structure are led out of electrodes through electroplated small pads. Metal bumps are processed on the small pads and integrated with the passive structure processed on the quartz substrate through flip - chip bonding. The simulation results show that the gain of this photonic antenna reaches 7.62 dBi at 285 GHz, and the E - plane pattern and 3D pattern are as Figure 8 shown. In the range of 275 - 296 GHz, the output gain is above 7 dBi, and the gain - frequency variation curve is as Figure 9 shown.

Claims

1. A photon antenna operating at 275 - 296 GHz, characterized in that, Specifically, it includes a UTC-PD body and a passive structure; the passive structure includes an impedance matching circuit, a power combiner circuit, and a Vivaldi antenna; There are two UTC-PD bodies in total. Each UTC-PD body adopts a double mesa structure. The two identical structures are both led out electrodes through electroplated small pads. Metal bumps are processed on each small pad, and electrical connection is generated with the passive structure processed on the quartz substrate through flip-chip bonding; The two UTC-PD bodies require two completely symmetrical impedance matching circuits; the impedance matching circuit is processed on a quartz substrate with a relative dielectric constant of 3.78 and is composed of a series transmission line, a short-circuited stub, and a MIM capacitor. Among them, both the series transmission line and the short-circuited stub exist in the form of a coplanar waveguide; After the impedance matching circuit, a T-junction power combiner is used to superimpose the two impedance-matched signals. The two input ends of the power combiner respectively correspond to the output ends of the two impedance matching circuits; The T-junction power combiner is composed of an input end, a quarter-wavelength impedance transformation part, and an output end; a Vivaldi antenna is connected after the output port of the power combiner, and the antenna is fed by a coplanar waveguide; The Vivaldi antenna is composed of a feeding end, a radiation structure, and a reflection structure; The feeding end adopts a coplanar waveguide structure, which is exactly the same as the structure of the third port of the T-junction power combiner; The radiation structure is composed of an exponentially varying open structure. In order to improve the gain, slots are opened on the radiation patch of the antenna, and metal blocks are added in the middle position of the dielectric substrate for guiding; in order to reduce the gain of the back lobe and side lobes, an arc-shaped reflection structure is designed on the back of the dielectric substrate.

2. The photonic antenna operating at 275 - 296 GHz as claimed in claim 1, wherein, The double mesa structure of the UTC-PD body from top to bottom is: a P-type ohmic contact layer, a blocking layer, an absorption layer, and a collection layer; The blocking layer includes a P-type blocking layer InP and a P-type blocking layer InGaAsP; The absorption layer includes a P-type heavily doped non-depleted absorption layer InGaAs and a P-type doped depleted absorption layer InGaAs; the absorption layer introduces a built-in electric field by means of gradient doping. The concentration difference brings about a potential difference, introducing a high electric field to accelerate electrons through the absorption layer; The collection layer includes an N-type doped cliff layer InP and an N-type lightly doped collection layer InP; the existence of the cliff layer InP increases the electric field of the absorption layer while reducing the electric field of the collection layer.

3. A photon antenna operating at 275 - 296 GHz as claimed in claim 1, characterized in that, The specific calculation formula for adjusting the load impedance of the UTC-PD is: First, the output impedance of the UTC-PD in a certain frequency band is: Z = m + j*n; Where m is the resistance and n is the reactance; Then, the impedance of the impedance matching circuit Z1 = a + j*c; Where a is the resistance and c is the reactance; Finally, calculate the impedance matching: that is, the impedance Z and Z1 satisfy: Z + Z1 = 50 + j*0, that is, the UTC-PD with the impedance matching circuit superimposed has an output resistance of 50 ohms and a reactance of zero in this frequency band.

4. A photon antenna operating at 275 - 296 GHz as claimed in claim 1, characterized in that, The input end of the T-junction power combiner has a length of 10um and a characteristic impedance of 50 ohms; the length of the quarter-wavelength impedance transformation part is 177um and the characteristic impedance is 70.7 ohms; the output end has a length of 30um and a characteristic impedance of fifty ohms.

5. A photon antenna operating at 275 - 296 GHz as claimed in claim 1, characterized in that, The width of the grooving is 30um, the groove pitch is 100um, and the height of the grooving starts from 200um and decreases in units of 50um.

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