High-output-power RTD terahertz oscillator based on Lienard equation

Abstract

The invention discloses a high-output-power RTD terahertz oscillator based on a Lienard equation. The oscillator is characterized in that a theoretical model of the RTD terahertz oscillator is constructed; collaborative design of output power and RTD device parameters is realized through analysis of a theoretical model; according to the structure of the RTD device, a core region is of a double-barrier quantum well structure, and an isolation layer, a lightly doped layer, a collector electrode, an emitter electrode, a collector electrode contact layer and an emitter electrode contact layer are arranged on the two sides of the core region respectively. Structural parameters of an RTD device are optimally designed, so that high-power output of the RTD terahertz oscillator is expected to be realized.

Description

Technical Field

[0001] The invention relates to the field of terahertz communication systems, and in particular to a high-output power RTD terahertz oscillator based on the Lienard equation. Background Art

[0002] With the promotion and application of emerging technologies such as virtual reality, ultra-high-definition video communication and intelligent manufacturing, the amount of data will show explosive growth in the future, and the demand for bandwidth and capacity of data communication will become increasingly strong. Although the current peak data transmission rate of 5G communication can reach 10Gbit / s, it still cannot meet the future bandwidth and capacity requirements. According to the expected development of future wireless communications, the transmission rate of 6G communication will be 10 to 100 times that of 5G communication, that is, the peak transmission rate will reach up to 1Tbit / s, and the current microwave / millimeter wave frequency band cannot provide sufficient bandwidth, so it is urgent to find spectrum resources with higher bandwidth.

[0003] Terahertz is between millimeter wave and far infrared bands, with abundant frequency resources and available working bandwidth of tens of GHz, which can meet the bandwidth requirements of Tbit / s data transmission rate, thus becoming a key candidate frequency band with great potential for 6G. At present, the confirmed terahertz communication frequency bands include: D band (110GHz~170GHz), G band (140GHz~220GHz) and H / J band (220GHz~330GHz). To realize terahertz communication in the above frequency bands, it is urgent to accelerate the research and development of terahertz devices and chips.

[0004] As the core component of terahertz communication, terahertz source is the key technical bottleneck restricting the development of terahertz communication. In particular, the output power directly determines the transmission distance of terahertz communication, and thus has become one of the current hot spots in terahertz research. At present, there are two main ways to generate terahertz waves: optical and electrical. Compared with the optical method, the all-solid-state electrical solution is easier to integrate and can realize miniaturized, low-power prototypes. Among many solid-state electronic devices, the oscillator based on the resonant tunneling diode (RTD) has the advantages of compact structure, low power consumption, room temperature operation and high oscillation frequency, making it the most promising terahertz source. [1] .

[0005] At present, there are designs for developing terahertz oscillators using the negative resistance characteristics of RTD. For example, Cimbri D et al. optimized the design of an RTD device structure using a quantum transport simulator. The simulation results show that the device is expected to provide an output power of up to 6mW for the oscillation circuit near 300GHz. However, they did not explain the theoretical basis and optimization design process for the high-power output of RTD. [2]In addition, Al-Khalidi A et al. proposed a design method for a J-band RTD terahertz oscillator based on circuit impedance analysis and developed an RTD terahertz oscillator using a short-circuited coplanar waveguide, which can achieve an output power of 1mW near 260GHz, but it is difficult to meet the power requirements of medium-distance terahertz wireless communication links. [3] At present, no relevant patents on the optimization design of RTD terahertz oscillators have been published in China.

[0006] In summary, in order to realize medium and long-distance terahertz communication, it is urgently necessary to develop high-output power RTD terahertz sources to provide strong technical support for future 6G communications.

[0007] References:

[0008] [1]Cimbri D,Wang J,Al-Khalidi A,et al.Resonant tunneling diodes high-speed terahertz wireless communications-Areview[J].IEEE Transactions onTerahertz Science and Technology,2022,12(3):226-244.

[0009] [2]Cimbri D,Morariu R,Ofiare A,et al.In 0.53 Ga 0.47 As / AlAs double-barrierresonant tunnelling diodes with high-power performance in the low-terahertzband[C]. 2022Fifth International Workshop on Mobile Terahertz Systems, 2022:1-5.

[0010] [3]Abdullah AK, Khalid HA, Wang J, et al. Resonant tunneling diodeterahertz sources with up to 1mW output power in the J-band[J]. IEEETransactions on Terahertz Science and Technology, 2020, 10(2): 150-157. Summary of the invention

[0011] Since the current design theory of RTD terahertz oscillators is incomplete and the output power is low, its practical application in medium and long-distance terahertz wireless communications is limited. To this end, the present invention proposes an RTD terahertz oscillator based on the Lienard equation, and optimizes the structural parameters of the RTD device to achieve high power output of the RTD terahertz oscillator. The RTD oscillator design proposed in the present invention is expected to be used in the actual research and development of high-power RTD terahertz oscillators, as described below:

[0012] A high output power RTD terahertz oscillator based on the Lienard equation, characterized in that the oscillator comprises:

[0013] Construct a theoretical model of RTD terahertz oscillator;

[0014] Through the analysis of theoretical models, the coordinated design of output power and RTD device parameters is achieved;

[0015] The structure of the RTD device includes: a core region is a double barrier quantum well structure, and on both sides of the core region are an isolation layer, a lightly doped layer, a collector and an emitter, a collector contact layer and an emitter contact layer.

[0016] The theoretical model is:

[0017]

[0018] Among them, τ, u, ε, and β are all model parameters, and their expressions are as follows:

[0019]

[0020]

[0021] Where v is the voltage across the controlled current source in the large-signal equivalent circuit model of the RTD device; a and b are fitting parameters; R S , C RTD are the contact resistance and capacitance of the RTD device; L is the resonant inductance of the RTD terahertz oscillator; R L is the impedance of the test instrument or antenna.

[0022] The coordinated design of the terahertz oscillator output power and RTD device parameters is as follows: for the double quantum well structure, the selection of the barrier layer thickness is a compromise; the thin quantum well enhances the binding ability of electrons in the quantum well, and the first binding energy level E in the well is 1 The distance from the bottom of the conduction band increases, thereby increasing the peak voltage V of the RTD p At the same time, E 1 With E2 The energy level spacing increases, which is manifested as the valley voltage V v The peak-to-valley voltage difference ΔV becomes larger; the isolation layer plays a role in blocking the diffusion of impurities in the RTD device structure. A thinner isolation layer reduces ΔV but has little effect on ΔI, increasing the a value; the doping concentration of the collector and emitter is 10 18 cm -3 To ensure sufficient number of carriers, the doping concentration of the contact layer is set at 10 19 cm -3 Magnitude.

[0023] The thickness of the barrier layer is 1.2 nm, the thickness of the quantum well is 4.1 nm, the thickness of the isolation layer is 1.5 nm, the thickness of the lightly doped layer is 25 nm, and the doping concentration is 2×10 16 cm -3 The collector electrode has a thickness of 160 nm and a doping concentration of 2×10 18 cm -3 ; The thickness of the emitter is 25nm and the doping concentration is 2×10 18 cm -3 The collector contact layer has a thickness of 40 nm and a doping concentration of 3×10 19 cm -3 ; The thickness of the emitter contact layer is 400nm and the doping concentration is 3×10 19 cm -3 .

[0024] The beneficial effects of the technical solution provided by the present invention are:

[0025] 1. Starting from the basic theory of RTD terahertz oscillator circuit, the present invention establishes a theoretical model based on the Lienard equation, and from the theoretical model, derives the basic conditions that need to be met when the RTD device outputs high power, thereby establishing the connection between the stable oscillation of the oscillator and the structure of the RTD device, realizing the coordinated design of the oscillator output power and the RTD device parameters, and providing a theoretical basis for the design of high-output power RTD terahertz oscillators;

[0026] 2. The contact resistance R is taken into account in the theoretical model of the RTD terahertz oscillator established by the present invention. S Therefore, the overall model is closer to the actual situation and can more comprehensively guide the design of high output power RTD terahertz oscillators.

[0027] 3. The RTD terahertz oscillator designed in the present invention has the advantages of high output power and short oscillation establishment time, and can be applied in medium and long-distance terahertz wireless communication links.

[0028] In summary, the high output power RTD terahertz oscillator design based on the Lienard equation proposed in the present invention has good application prospects in practical applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a typical circuit diagram of an RTD terahertz oscillator;

[0030] Figure 2 is the equivalent circuit diagram of the RTD oscillator resonant circuit;

[0031] Figure 3 Schematic diagram of the classic structure of double barrier quantum well RTD;

[0032] Figure 4 Schematic diagram of optimized RTD device structure;

[0033] Figure 5 Comparison of the current-voltage characteristic curves of the RTD device before and after optimization;

[0034] Figure 6 Time domain waveform of the RTD oscillator before optimization;

[0035] Figure 7 This is the time domain waveform of the optimized RTD oscillator;

[0036] Figure 8 Spectrum diagram of the RTD oscillator before optimization;

[0037] Fig. 9 This is the spectrum diagram of the optimized RTD oscillator. DETAILED DESCRIPTION

[0038] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention are described in further detail below.

[0039] The embodiment of the present invention proposes a high output power RTD terahertz oscillator based on the Lienard equation, and the terahertz oscillator includes:

[0040] 1. Theoretical model of RTD terahertz oscillator

[0041] The typical circuit topology of RTD terahertz oscillator is as follows: Figure 1 As shown in the figure, it mainly consists of two parts: DC bias circuit and resonant circuit. The DC bias circuit includes: bias voltage source V BIAS , Bias line resistance R B , bias line inductance L B , stabilizing resistor R E and decoupling capacitor C E .

[0042] Among them, the stabilizing resistor R E The function of the decoupling capacitor C is to suppress low-frequency oscillation. E is the oscillation frequency f osc The stabilizing resistor R E Short circuit, so that the resonant inductor L is grounded. The resonant circuit consists of RTD, resonant inductor L, and DC blocking capacitor C. block and load R L The resonant inductor L can be realized by a short-circuited transmission line and realize LC resonance with the capacitance of the RTD device; the DC blocking capacitor C block The purpose is to isolate the resonant circuit from the subsequent load to avoid signal crosstalk. L It is the impedance of the test instrument or antenna, usually 50Ω.

[0043] Will Figure 1 The RTD device in the circuit is replaced by a large signal equivalent circuit model, and the circuit is transformed using circuit analysis theory to obtain the following: Figure 2 The equivalent circuit model of the RTD terahertz oscillator is shown in Figure 2. RTD represents the RTD capacitance, R S is the series resistance of the RTD, i(v) represents the current-voltage characteristic of the RTD device, and the third-order approximation model is usually used, that is:

[0044] i(v)=-av+bv 3 (1) Where v is the voltage across the RTD capacitor and the controlled current source, a and b are fitting parameters, which are determined by the specific current-voltage characteristic curve of the RTD device. Their specific expressions are:

[0045]

[0046] Where ΔV and ΔI are the peak-to-valley voltage difference and peak-to-valley current difference of the current-voltage characteristic curve of the RTD device, respectively. Figure 2 For the circuit shown, Kirchhoff's current and voltage laws give:

[0047] i+i 1 +i 2 =0 (4)

[0048] i 2 =i 3 +i 4 (5)

[0049] i 2 R s +i 4 R L =v (6) Where i is the current-voltage characteristic of the RTD device, which is equivalent to the third-order approximate model in formula (1); i1 is the current flowing through the RTD device capacitance C RTD The current i 2 is the current flowing through the RTD device contact resistance R S The current i 3 is the current flowing through the resonant inductor L; i 4 is the current flowing through the load R L of current.

[0050] Among them, the currents of the capacitor and inductor branches can be expressed as:

[0051]

[0052] Substituting equation (1) and equation (4) into equation (5), we get:

[0053]

[0054] Combining equations (5) and (6), we can get:

[0055]

[0056] Substituting equations (9) and (10) into equation (5), and then substituting equation (5) into equation (4), we can obtain:

[0057]

[0058] Taking the derivative of both sides of equation (11) with respect to t, we can get:

[0059]

[0060] If:

[0061]

[0062] Then formula (12) can be simplified to the following form:

[0063]

[0064] For complex dynamic systems, the Lienard equation is often used to analyze the working state of the system. Its general expression is:

[0065]

[0066] Among them, f(x) describes the attenuation of the system, g(x) represents the nonlinear effect of the system, and the working state of the system is determined by the specific forms of f(x) and g(x). When f(0)<0, xg(x)>0(x≠0), equation (18) has a real number solution, that is, the system can work stably in oscillation.

[0067] Comparing equation (17) and equation (18), we find that if -ε(1-u 2 )=f(x),u+βu 3 =g(x), then the above two equations have exactly the same form, namely Figure 2 The RTD oscillator circuit shown can be analyzed and discussed using the Lienard equation.

[0068] According to the analytical theory of the Lienard equation, if the RTD terahertz oscillator described by equation (17) is to be ensured to oscillate stably, f(0)<0, ug(u)>0 (u≠0) must be satisfied.

[0069] Substituting equations (13)-(16) into equation (17), we can obtain that both ε and β should be greater than 0 and both are real numbers, that is:

[0070] aL(R L +R s )-C RTD R L R s -L>0 (19)

[0071] 1-aR s >0 (201

[0072] By solving equations (19) and (20) together, we can obtain the following conditions that need to be met when the RTD oscillator oscillates stably:

[0073]

[0074] It can be seen from the above formula that to ensure stable oscillation of the RTD oscillator, the value of a should be selected reasonably.

[0075] 2. RTD device structure design for high output power

[0076] In order to improve the output power of the RTD terahertz oscillator, the following analysis is conducted from the perspective of a theoretical model based on the Lienard equation.

[0077] According to the theoretical analysis of the Lienard equation, the sinusoidal oscillation amplitude of the RTD oscillator is proportional to the ε value, which means that the larger the oscillation amplitude, the greater the output power of the RTD oscillator. However, an excessively large ε value will make the oscillation waveform non-sinusoidal, so it is necessary to take comprehensive considerations during design. According to the simulation results of formula (15), when the parameter values ​​of other components remain unchanged, the ε value increases with the increase of the a value of the RTD device, and decreases with the RTD capacitance value C. RTD In the actual RTD device design, the change range of a value is much larger than that of C RTD Therefore, the design of high-power RTD terahertz oscillator mainly revolves around the a value of the RTD device.

[0078] From formula (2), we can know that to obtain a large a value, we can increase the ΔI parameter of the RTD device current-voltage characteristic curve or reduce the ΔV parameter. In the actual design process of the RTD device, it is mainly achieved by optimizing the device structure parameters. The following discusses the thickness of each layer of material in the RTD device structure, in order to achieve a specific way to obtain a larger a value:

[0079] First, for the double quantum well structure, a thin barrier layer can significantly increase the probability of electrons tunneling through the barrier, which greatly increases the current parameter ΔI of the RTD device, while not causing a significant change in the voltage parameter ΔV, thereby increasing the a value. However, the barrier layer cannot be too thin, otherwise, although a high current density can be obtained, the peak-to-valley current ratio of the device will be limited. Therefore, the selection of the barrier layer thickness must be considered as a compromise.

[0080] Secondly, the thin quantum well can enhance the binding ability of electrons in the quantum well, making the first binding energy level E 1 The distance from the bottom of the conduction band increases, thereby increasing the peak voltage V of the RTD p At the same time, E 1 With E 2 The energy level spacing also increases, which is manifested as the valley voltage V v Theoretical analysis shows that the effect of thin quantum wells on the increase of ΔI is much greater than that on ΔV, so a properly selected quantum well thickness can also increase the a value.

[0081] Thirdly, the isolation layer plays a role in blocking the diffusion of impurities in the RTD device structure. A thinner isolation layer can reduce ΔV, but has little effect on ΔI, so the a value can be increased. In addition, a thin isolation layer can also prevent the electrons from gathering in the triangular potential well on the emitter side when an external bias is applied, thereby avoiding 2D-2D tunneling.

[0082] Finally, the thickness of the collector and emitter has little effect on the current-voltage characteristics of the RTD device. 18 cm -3 In order to reduce the contact resistance of the RTD device, the doping concentration of the contact layer is set at 10 19 cm -3 order of magnitude in order to achieve ohmic contact between metal and semiconductor.

[0083] Based on the above-established RTD terahertz oscillator theoretical model and the guiding ideology of RTD device structure design, a high-output power RTD terahertz oscillator is specifically designed below.

[0084] Figure 3The figure shows the classic structure of the double barrier quantum well RTD. The thickness of each layer and the corresponding doping concentration are given in the figure. In order to obtain the current-voltage characteristics of the classic structure RTD device, the non-equilibrium Green's function simulator WinGreen is first used to simulate the structure RTD. Its current-voltage characteristics are shown in Figure 5 In order to highlight the beneficial effects of the embodiments of the present invention, the thickness of each layer of the classic structure RTD is optimized according to the WinGreen simulation results, and the reasonable range of a is determined. The optimized RTD device structure is shown in FIG. Figure 4 As shown, the doping concentration of each layer remains unchanged, and the specific changes in the thickness of the material layer are: the thickness of the barrier layer is reduced from 1.4nm to 1.2nm, the thickness of the quantum well is reduced from 4.5nm to 4.1nm, and the thickness of the isolation layer is reduced from 10nm to 1.5nm.

[0085] By simulating the optimized RTD using the non-equilibrium Green's function simulator WinGreen, we can get its corresponding current-voltage characteristic curve, such as Figure 5 The middle dotted line shows that by comparing the current-voltage characteristic curves before and after optimization, it can be seen that the current change ΔI of the RTD device is more obvious after optimization. Although ΔV also increases, the a value of the device after optimization is significantly greater than that before optimization.

[0086] According to the working mechanism of the RTD device, a physically based equivalent circuit model can be established. The conductance and capacitance in the model can be expressed by the following formula:

[0087]

[0088] Among them, C 0 and C qw are the geometric capacitance and quantum capacitance of the RTD device, A is the area of ​​the RTD device, and t qw ,t b and t dep represent the thickness of quantum well, barrier layer and depletion layer respectively, ε qw , ε b and ε dep are the relative dielectric constants of the quantum well, barrier layer, and depletion layer, respectively, and ε 0 is the dielectric constant of vacuum, is the reduced Planck constant, Γ 1 is the full width at half maximum of the first transmission coefficient peak, v s is the electron saturation drift velocity.

[0089] According to equations (22) and (23), for a 4×4μm 2 For RTD devices, the conductivity G of the RTD before and after optimization can be obtained from the calculation results of the non-equilibrium Green's function simulator WinGreen.RTD are -31mS and -109mS respectively, and the device capacitance C RTD 58.72fF and 65.6fF respectively. In the embodiment of the present invention, R s Take 1Ω, and set the oscillation frequency to 260GHz. The resonant inductance L corresponding to 260GHz can be calculated to be 5.82pH and 5.09pH respectively. According to formula (16), the ε values ​​of the RTD terahertz oscillator before and after optimization are 0.015 and 0.723 respectively. Therefore, the output power of the RTD terahertz oscillator will be significantly improved after optimization.

[0090] Based on the RTD device equivalent circuit model parameters calculated above, the following is established in the ADS circuit simulation software: Figure 1 The RTD terahertz oscillation circuit shown in the figure. B and L B Set to 1Ω and 56nH respectively, R E Take 10Ω, C E and C block Take 2pF and 0.5pF respectively, load R L The ADS circuit simulation software is then used to perform transient simulation to obtain the time domain waveform of the RTD oscillator. Figure 6 is the time domain waveform of the RTD oscillator before optimization, and Figure 7 This is the time domain waveform of the optimized RTD oscillator, in which the transient simulation time is set to 10ns. As can be seen from the figure, the oscillation amplitude of the RTD oscillator before optimization is 188mV, and the oscillation establishment time is 4.5ns. After optimization, the oscillation amplitude of the RTD oscillator increases to 1.2V, and the oscillation establishment time is shortened to 0.1ns.

[0091] Figure 8 and Fig. 9 The spectrum diagram of the RTD oscillator before and after optimization. As can be seen from the figure, the RTD terahertz oscillator oscillates stably at 260GHz before and after optimization. The output power before optimization is -5.383dBm (0.29mW), and after optimization it increases to 7.916dBm (6.19mW), achieving a twenty-fold power increase. In addition, the oscillation establishment time of the RTD terahertz oscillator after optimization is also significantly reduced, which greatly improves the frequency response performance of the oscillator.

[0092] In summary, the RTD terahertz oscillator design based on the Lienard equation proposed in the embodiment of the present invention not only obtains stable frequency oscillation and short settling time, but also realizes high power output. Compared with the traditional design, the embodiment of the present invention starts from the basic theory of circuit analysis and establishes a theoretical model of the RTD terahertz oscillator based on the Lienard equation. Through the theoretical model analysis, the coordinated design of the terahertz oscillator output power and the RTD device parameters can be realized, which provides theoretical support for the design of high-power RTD oscillators. The design proposed in the embodiment of the present invention is expected to be used in the actual research and development of high-output power RTD terahertz oscillators.

[0093] Unless otherwise specified, the models of the components in the embodiments of the present invention are not limited, and any device that can perform the above functions may be used.

[0094] Those skilled in the art will appreciate that the accompanying drawing is only a schematic diagram of a preferred embodiment, and the serial numbers of the embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0095] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A high output power RTD terahertz oscillator based on Lienard equation, characterized in that: The oscillator comprises: Construct a theoretical model of RTD terahertz oscillator; Through the analysis of theoretical models, the coordinated design of output power and RTD device parameters is achieved; The structure of the RTD device includes: a core region is a double barrier quantum well structure, and on both sides of the core region are an isolation layer, a lightly doped layer, a collector and an emitter, a collector contact layer and an emitter contact layer.

2. A high output power RTD terahertz oscillator based on the Lienard equation according to claim 1, characterized in that: The theoretical model is: Among them, τ, u, ε, and β are all model parameters, and their expressions are as follows: Where v is the voltage across the controlled current source in the large-signal equivalent circuit model of the RTD device; a and b are fitting parameters; R S , C RTD are the contact resistance and capacitance of the RTD device; L is the resonant inductance of the RTD terahertz oscillator; R L is the impedance of the test instrument or antenna.

3. The high output power RTD terahertz oscillator based on the Lienard equation according to claim 1, characterized in that: The coordinated design of the terahertz oscillator output power and RTD device parameters is: For double quantum well structures, the selection of barrier layer thickness is a compromise; The thin quantum well enhances the binding ability of electrons in the quantum well, and the distance between the first bound energy level E1 in the well and the bottom of the conduction band increases, thereby increasing the peak voltage V of the RTD. p At the same time, the energy level gap between E1 and E2 increases, which is manifested as the valley voltage V v and the peak-to-valley voltage difference ΔV becomes larger; The isolation layer plays a role in blocking the diffusion of impurities in the RTD device structure. A thinner isolation layer reduces ΔV, but has little effect on ΔI and increases the a value. The doping concentration of the collector and emitter is 10 18 cm -3 To ensure sufficient number of carriers, the doping concentration of the contact layer is set at 10 19 cm -3 Magnitude.

4. The high output power RTD terahertz oscillator based on the Lienard equation according to claim 1, characterized in that: The thickness of the barrier layer is 1.2 nm, and the thickness of the quantum well is 4.1 nm.

5. The high output power RTD terahertz oscillator based on the Lienard equation according to claim 1, characterized in that: The thickness of the isolation layer is 1.5 nm, the thickness of the lightly doped layer is 25 nm, and the doping concentration is 2×10 16 cm -3 .

6. The high output power RTD terahertz oscillator based on the Lienard equation according to claim 1, characterized in that: The collector electrode has a thickness of 160 nm and a doping concentration of 2×10 18 cm -3 ; The thickness of the emitter is 25nm and the doping concentration is 2×10 18 cm -3 .

7. The high output power RTD terahertz oscillator based on the Lienard equation according to claim 1, characterized in that: The collector contact layer has a thickness of 40 nm and a doping concentration of 3×10 19 cm -3 ; The thickness of the emitter contact layer is 400nm and the doping concentration is 3×10 19 cm -3 .

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