JP2022137856A - terahertz oscillator - Google Patents

Abstract

To provide a high-output terahertz oscillator that oscillates even at high frequencies of 1 THz or higher, without a MIM capacitor structure which is complicated in a structure and complicated to be manufactured, by the resonance of an RTD, a split ring resonator, and a stabilizing resistor.SOLUTION: In a terahertz oscillator, a split ring resonator is formed between a first coplanar strip line and a second coplanar strip line to which a bias voltage is applied, a stabilizing resistor connected between the first and second coplanar strip lines adjacent to the split ring resonator, an RTD is provided through a mesa on the second coplanar strip line, a conductive piece forming an air bridge is suspended between the first coplanar strip line and the mesa, and the terahertz oscillator oscillates through the resonance of the RTD, the split ring resonator, and the stabilizing resistor.SELECTED DRAWING: Figure 11

Description

There is an application for the application of Article 30, Paragraph 2 of the Patent Act. Website name: The 81st Autumn Meeting of the Japan Society of Applied Physics (Publication presentation by proceedings) ▼) Top address: https://meeting. jsap. or. jp/jsap2020a/ Publication address: (Lecture number: 10p-Z24-15) https://confit. atlas. jp/guide/event/jsap2020a/subject/10p-Z24-15/tables? cryptoId = Date posted on the website: August 26, 2020 Name of the meeting: The 81st JSAP Autumn Meeting (Oral presentation held online) (Items ▲ 3 ▼ to ▲ 6 of the objective evidence materials in the list of submitted properties) ▼) Meeting address: https://meeting. jsap. or. jp/jsap2020a/ Date: September 10, 2020 Lecture number: 10p-Z24-15

The present invention relates to a terahertz oscillator that oscillates at a frequency in the terahertz (THz) frequency band located between radio waves and light waves. This relates to a terahertz oscillator using a Resonant Tunneling Diode and a split-ring resonator (SRR).

The terahertz (THz) frequency band (approximately 0.1 THz to 10 THz), which is located between radio waves and light waves, is an undeveloped frequency band. . For that purpose, development of a small terahertz oscillator is essential. As one of them, a terahertz oscillator using a double-barrier resonant tunneling diode (RTD) element with a semiconductor nanostructure has been studied. This terahertz oscillator is currently the only electronic device that can oscillate at a frequency of 1 to 2 THz at room temperature. However, this terahertz oscillator has a very small output of about 10 μW, and has a problem that manufacturing is complicated and complex.

FIG. 1 shows an example of the structure of a conventional terahertz oscillator, in which a lower electrode 4 is layered on an InP substrate 3 of about 1 mm square, and an elongated (10 to 20 μm) concave portion is formed almost at the center of the lower electrode 4 . A slot antenna 2 consisting of is arranged. Further, an upper electrode 5 and a stabilizing resistor (resistance value R _S ) 6 are arranged on the InP substrate 3, and an MIM (Metal Insulator Metal) capacitor 7 is connected to the tip of the upper electrode 5, as shown in FIG. A resonant tunneling diode (RTD) 1 having a negative V(voltage)-I(current) characteristic is provided. A stabilizing resistor 6 is connected between the lower electrode 4 and the upper electrode 5 for stabilizing the oscillation operation, and the stabilizing resistor 6 is composed of, for example, an InGaAs sheet. The upper electrode 5 is grounded and the lower electrode 4 is applied with a DC bias (bias voltage Vb). When a DC bias voltage Vb is applied to the resonant tunneling diode (RTD) 1, electrons tunnel through the quantum level in the well, and a tunnel current flows. When the inner quantum level becomes lower than the bottom of the conduction band of the emitter, electrons cannot tunnel and the current decreases, resulting in the VI characteristic as shown in FIG. Electromagnetic waves can be oscillated and amplified by using the differential negative resistance characteristic “-G _RTD ” in which the current decreases. Also, the resonant tunneling diode (RTD) 1 has a parasitic capacitance C _RTD in parallel with the differential negative resistance “−G _RTD ”, and as shown in FIG. be done. The output is determined by the radiation resistance of slot antenna 2 .

Thus, the conventional terahertz oscillator has a resonance structure of RTD1 and MIM capacitor 7, and slot antenna 2 is formed by MIM capacitance C _MIM and RTD1 of MIM capacitor 7. FIG. Since the slot antenna 2 is represented by the LC resonance circuit and the radiation loss _Gant , the equivalent circuit of this oscillator is the circuit shown in FIG. The oscillation start condition is when the positive value G _RTD of the differential negative resistance characteristic becomes equal to or greater than the radiation loss G _ant as shown in Equation 1 below, and oscillation occurs at the frequency f _OSC shown in Equation 2 below.

また、バイアス回路（バイアス電圧Ｖｂ）を含む発振器の等価回路は図５に示すようになっており、ＭＩＭキャパシタ７のＭＩＭキャパシタンスＣ_ＭＩＭと安定化抵抗６の抵抗値Ｒ_Ｓとが並列接続され、ＲＴＤ１とＭＩＭキャパシタンスＣ_ＭＩＭとの間にスロットアンテナ２のインダクタンスＬ_Ｓが存在し、バイアス回路と抵抗値Ｒ_Ｓとの間に回線のインダクタンスＬ_Ｗが存在している。スロットアンテナ２の周辺には図１に示すような周回電流ｉが流れ、周回電流ｉに起因したインダクタンスＬ_Ｓが形成される。そして、図５の等価回路において、高周波ではＭＩＭキャパシタンスＣ_ＭＩＭが短絡してインダクタンスＬ_Ｗが開放されるので、図６（Ａ）に示すようにＲＴＤ１とインダクタンスＬ_Ｓの共振回路となる。また、低周波ではインダクタンスＬ_Ｓ及びＬ_Ｗが無視され、抵抗値Ｒ_ＳがＲＴＤ１の微分負性抵抗“－Ｇ_ＲＴＤ”を打ち消すので、図６（Ｂ）に示すようにＲＴＤ１、バイアス電圧Ｖｂ及び安定化抵抗６の抵抗値Ｒ_Ｓの共振回路となる。

The equivalent circuit of the oscillator including the bias circuit ( _bias voltage _Vb ) is as shown in FIG. There is an inductance _LS of the slot antenna 2 between the RTD 1 and the _MIM capacitance _CMIM , and a line inductance _LW between the bias circuit and the resistance value RS. A circulating current i as shown in FIG. 1 flows around the slot antenna 2, and an inductance _LS is formed due to the circulating current i. In the equivalent circuit of FIG. 5, at high frequencies, the _MIM capacitance CMIM is short-circuited and the inductance LW is opened, resulting in a resonant circuit of the _RTD1 and the inductance _LS as shown in FIG. 6(A). At low frequencies, the inductances L _S and L _W are ignored, and the resistance value R _S cancels the differential negative resistance "-G _RTD " of the RTD1. A resonance circuit of the resistance value R _S of the stabilizing resistor 6 is formed.

JP 2013-171966 A JP 2006-210585 A WO2015/170425 Japanese Patent No. 6570187

M. Asada, S. Suzuki, and N. Kishimoto, “Resonant tunneling diodes for sub-terahertz and terahertz oscillators”, Japanese Journal of Applied Physics, vol. 47, no. 6, pp. 4375-4384, 2008. M. Asada and S. Suzuki, “Room-temperature oscillation of resonant tunneling diodes close to 2 THz and their functions for various applications”, Journal of Infrared, Millimeter, and Terahertz Waves, vol. 37, pp. 1185-1198, 2016. T. Van Mai, Y. Suzuki, X. Yu, S. Suzuki, and M. Asada, “Structure-Simplified Resonant-Tunneling-Diode Terahertz Oscillator Without Metal-Insulator-Metal Capacitors”, Journal of Infrared, Millimeter, and Terahertz Waves, vol. 41, pp. 1498-1507, 2020.

Since the terahertz oscillator described above has an MIM capacitor for separating the terahertz oscillator circuit and the baseband circuit, it has a complicated structure and is complicated to manufacture. Therefore, a terahertz oscillator without the MIM capacitor has also been proposed (Non-Patent Document 3), and attempts are made to greatly simplify the structure and manufacturing process. However, since an oscillator without MIM capacitors has a large loss, it is difficult to oscillate at a high frequency exceeding 1 THz, which is possible with oscillators with MIM capacitors, and optimization of the structure is required.

Therefore, a slot antenna type terahertz oscillator without an MIM capacitor has been proposed (PCT/JP2021/000069). In the following, the outline will be explained assuming that this is a slot antenna oscillator or a slot resonator.

FIG. 7 is a perspective view of the slot antenna oscillator 10. The end surface of the electrode plate 15 facing the slot portion surrounded by the stabilizing resistors 13 and 14 is the slot antenna 12 (approximately 12 μm). An elongated conductive member 18 is provided in the central portion of the. The RTD 11 is connected to the tip of the conductive member 18 via a mesa, and the lower portion of the conductive member 18 has an air bridge structure forming a slot. The slot antenna oscillator 10 does not have an MIM capacitor structure, and has an electrode plate 15 connected to a grounded bias pad 15A and a rectangular electrode plate 16 connected to a bias pad 16A for applying a DC bias Vb. A slot is provided between the end surface of the electrode plate 15 and the opposite end surface of the electrode plate 16, and the end surface of the electrode plate 16 facing the slot becomes the slot antenna 12, and the electrode plate 15 and the electrode plate 16 are arranged on both sides. It is connected by two stabilizing resistors 13 and 14 . The electrode plate 15 has a square concave portion in a plane facing the slot antenna 12, and a resonant tunneling diode (RTD) 11 is provided in the concave portion. A conductive member 18 is suspended between the RTD 11 and the electrode plate 16, and the slot has an air bridge structure.

The equivalent circuit of the slot _{antenna oscillator} 10 is shown in FIG. and 14 (total resistance R _S of both) are connected in parallel to RTD 11 . At low frequencies, the inductances _Lw and _Ls can be regarded as a short circuit, and the resistance value _Rs of the stabilizing resistors 13 and 14 cancels the negative differential resistance (NDR) of the RTD 11, so the equivalent circuit is shown in FIG. (B). On the other hand, at a high frequency such as _terahertz , the impedance of the _{inductance LW} becomes large and the bias circuit 17 is cut off. ), but since the loss G of the resistance value _RS of the stabilizing resistors 13 and 14 is small, the inductance _LS and the capacitance in the RTD 11 resonate and oscillate. That is, if f is the oscillation frequency of the oscillator, the angular frequency ω is ω=2πf, and the loss G of the resistance value _RS is expressed by the following equation (3).

そして、抵抗値Ｒ_Ｓは小さい値（数Ω）であるので、数３における“Ｒ_Ｓ ^２”は略ゼロとなる。従って、数３は下記数４で近似できる。

Since the resistance value R _S is a small value (several Ω), "R _S ² " in Expression 3 is approximately zero. Therefore, Equation 3 can be approximated by Equation 4 below.

数４において、角周波数ωの２乗“ω^２”は、テラヘルツ周波数では大きな値であるので数４は略ゼロとなり、抵抗値Ｒ_Ｓの損失Ｇは無視できる。そのため、インダクタンスＬ_ＳとＲＴＤ１１内のキャパシタンスとで共振して発振する。

In Equation 4, since the square of the angular frequency ω "ω ² " is a large value at the terahertz frequency, Equation 4 becomes substantially zero, and the loss G of the resistance value _RS can be ignored. Therefore, the inductance _LS and the capacitance in the RTD 11 resonate and oscillate.

FIG. 10 shows an example of the output characteristics of the slot antenna oscillator 10. It is difficult to oscillate at a high frequency exceeding 1 THz, which was possible with an oscillator having an MIM capacitor structure, and optimization of the structure is required. The characteristics of FIG. 10 are the current density Jp=8 [mA/μm ² ] which is the RTD parameter, the voltage difference ΔV between the peak point and the valley point ΔV=0.5 [V], and the current ratio PVCR between the peak point and the valley point. =3.

The present invention has been made in view of the circumstances as described above, and an object of the present invention is to eliminate the MIM capacitor structure, which is complicated in structure and complicated to manufacture, and to achieve the resonance of the RTD, the split ring resonator, and the stabilization resistor. , to provide a high output terahertz oscillator that oscillates even at a high frequency of 1 THz or more.

The present invention relates to a terahertz oscillator with a resonant tunneling diode (RTD). and a stabilizing resistor connected between the first coplanar stripline and the second coplanar stripline adjacent to the split ring resonator to form a mesa on the second coplanar stripline. a resonant tunneling diode (RTD) through a conductive strip suspended between said first coplanar stripline and said mesa to form an air bridge, said RTD and said split ring resonator; This is achieved by oscillating through resonance with the stabilizing resistor.

In addition, the above object of the present invention is such that the split ring resonator is composed of a recessed space provided in the first coplanar strip line and two recessed spaces provided in the second coplanar strip line. By forming in a U-shape, or by providing a U-shaped resonance space around the mesa of the second coplanar strip line, or by the tip of the conductive piece It is a rectangular conductor portion, and the conductor portion is layered on the mesa, or the first coplanar strip line and the second coplanar strip line are connected to the second coplanar strip line via bias paths, respectively. More effectively achieved by being connected to one bias pad and a second bias pad, or by providing the RTD on the n+InP etch stopper of the second coplanar stripline. be done.

According to the present invention, it does not have a metal (conductive material)/insulator/metal (conductive material) MIM capacitor structure, and has a double-barrier resonant tunneling diode (RTD), a split ring resonator, and a stabilization resistor. Due to the resonance of , the electric field is concentrated in the center of the split ring, and the confinement is improved, so that oscillation in the terahertz frequency band of 1 THz or more can be obtained at high output.

The two coplanar striplines outside the split ring resonator act as dipole antennas and can be tuned by the dimensions of the coplanar striplines to meet the matching conditions to extract maximum output from the RTD.

It is a perspective structural view showing an example of a terahertz oscillator using a conventional RTD. FIG. 3 is a schematic diagram showing an output example of a terahertz oscillator using a conventional RTD; FIG. 3 is a characteristic diagram showing an example of RTD characteristics; It is an equivalent circuit diagram of a terahertz oscillator using a conventional RTD. FIG. 11 is an oscillation equivalent circuit diagram including a bias circuit of a terahertz oscillator using a conventional RTD. It is an equivalent circuit diagram showing a high frequency circuit and a low frequency circuit. 1 is a perspective structural view showing an example of a conventional slot antenna oscillator; FIG. 1 is an equivalent circuit diagram of a conventional slot antenna oscillator; FIG. It is an equivalent circuit diagram of the slot antenna oscillator at high and low frequencies. FIG. 4 is an output characteristic diagram of a slot antenna oscillator; 1 is a perspective structural view showing a structural example of a terahertz oscillator according to the present invention; FIG. 1 is a plan structural view showing in detail a structural example of a terahertz oscillator according to the present invention; FIG. FIG. 12 is a cross-sectional view taken along the line XX' of FIG. 11; 12 is a cross-sectional view taken along line Y-Y' of FIG. 11; FIG. FIG. 12 is a cross-sectional view taken along line ZZ' of FIG. 11; 1 is a planar structure and an equivalent circuit diagram of a terahertz oscillator according to the present invention; FIG. 1 is an equivalent circuit diagram of a terahertz oscillator according to the present invention; FIG. FIG. 4 is a characteristic diagram showing conductance and loss for the present invention and a conventional example; It is an electric field distribution diagram showing an example of the calculation result of the electric field distribution (the present invention and the conventional example). FIG. 5 is a characteristic diagram showing oscillation characteristics of the present invention in comparison with a conventional example; FIG. 4 is a characteristic diagram showing the relationship between the length d of the coplanar stripline and the radiation efficiency; FIG. 4 is a characteristic diagram showing an example of characteristics of the size of an RTD mesa and an oscillation frequency in comparison with a slot resonator; FIG. 4 is a characteristic diagram showing frequency characteristics of conductance; FIG. 4 is a characteristic diagram showing the relationship between RTD mesa and oscillation frequency; FIG. 3 is a characteristic diagram showing frequency characteristics of radiation efficiency; FIG. 4 is a characteristic diagram showing frequency characteristics of output power; 1 is a plan view of a fabricated terahertz oscillator according to the present invention; FIG. FIG. 4A is a characteristic diagram showing the RTD mesa size of the output frequency, and FIG. 4B is a characteristic diagram showing the frequency of the output power. 1 is a connection diagram showing a connection example of a large-scale array in which a large number of terahertz oscillators according to the present invention are connected; FIG. FIG. 4 is a schematic diagram showing how a large-scale array is used as a high-speed modulator; FIG. 4 is a schematic diagram showing how a large-scale array is used as a highly sensitive sensor. FIG. 4 is a schematic diagram showing how a large-scale array is used as a high-power array light source;

The present invention is a terahertz oscillator using a double-barrier resonant tunneling diode (RTD), which has a structure without an MIM (Metal Insulator Metal) capacitor structure composed of metal (conductor)/insulator/metal (conductor). be. Since it does not have an MIM capacitor structure, the structure is simple, and the number of steps in the manufacturing process can be significantly reduced compared to conventional devices. can get. In addition, the split ring resonator concentrates the electric field in the center and improves the confinement, so the loss is smaller than that of the slot resonator, and high output can be obtained.

According to the terahertz oscillator of the present invention, the two coplanar strip lines outside the split ring resonator act as dipole antennas, and the dimensions of the coplanar strip lines can be adjusted to provide a matching condition for extracting the maximum output from the RTD. It is possible to meet

In addition, the terahertz oscillator of the present invention is expected to be applied to imaging, high-speed communication, etc., and by forming a large-scale array, it can be applied to high-speed modulators, high-sensitivity sensors, high-output array light sources, etc. be.

Embodiments of the present invention will be described below with reference to the drawings.

A terahertz oscillator 100 according to the present invention has an overall structure as shown in FIGS. The oscillator 100A arranged between the bias pads 110 and 111 has a structure as shown in FIGS. That is, the entire terahertz oscillator 100 is layered on an Sl-InP substrate 101, and in the space (45 μm wide) between two conductive material bias pads 110 and 111, a An oscillation section 100A is formed as shown in 12(B). Details of the oscillator 100A are shown in plan views of FIGS. 12C and 12D and cross-sectional views of FIGS. 13 to 15. FIG.

The oscillation unit 100A is provided with rectangular coplanar striplines (10 μm width × 70 μm length, Ti/Pd/Au) 120 and 121, which are two conductor plates facing each other (with an interval of 5 μm). Since the coplanar strip lines 120 and 121 function as dipole antennas, they are sometimes referred to as "CPS antennas" below. Central portions of the coplanar strip lines 120 and 121 form a generally U-shaped space (ring), and form a split ring resonator 130 in cooperation with an RTD 140 and stabilizing resistors 122 and 123, which will be described later. ing. Coplanar stripline 120 is connected to bias pad 110 through bias passage 120A, and coplanar stripline 121 is connected to bias pad 111 through bias passage 121A. The central portion of the coplanar stripline 120 is formed with two concave portions 120-1 and 120-2 (rings) on both sides of a long conductor piece 131, and the central portion of the coplanar stripline 121 is formed with a rectangular convex portion 121- 1, and two concave portions 121-2 and 120-3 having rectangular cross sections are formed (strips) on both sides of the convex portion 121-1, forming a U-shaped space portion (strip ring) as a whole. ing. The conductor piece 131 is suspended in the space (ring) so as to form an air bridge. Also, the coplanar strip lines 120 and 121 are connected by stabilizing resistors (width of 2 μm) 122 and 123 arranged adjacent to both ends of the split ring resonator 130 . A combined resistance value of the stabilizing resistors 122 and 123 is "Rs".

As shown in FIGS. 12C and 12D, the tip of the conductor piece 131 of the coplanar strip line 120 is a rectangular conductor portion 131A. Reaching the tip, RTD 140 is formed and RTD mesa 142 is formed. A convex portion 121-1 of the coplanar strip line 121 is formed with a resonance space portion 141, which is a U-shaped concave portion surrounding the conductor portion 131A.

FIG. 13 is a cross-sectional view taken along the line XX' of FIG. It has a layer structure of an upper etch stopper n+InP layer 103 and an RTD 140 layered on this n+InP layer (etch stopper layer) 103, and Ti/Pd layered thereon. /Au coplanar strip lines 120 and 121 are formed with a space (interval of 5 μm) between them.

FIG. 14 is a cross-sectional view taken along the line YY' of FIG. 11. At this position, the layer structure is the same as that of FIG. are connected without gaps. This forms a stabilizing resistor 122 . The symmetrical side stabilization resistor 123 has a similar structure.

FIG. 15 is a ZZ' sectional view of FIG. 11, in which the n+InGaAs layer 102 under the conductor piece 131, the n+InP layer 103 thereon, and the RTD 140 on the n+InP layer 103 form an air bridge. The RTD 140 below the conductor portion 131A becomes the RTD mesa 142. As shown in FIG. A resonance space portion 141 is formed between the coplanar strip line 121 and RTD 140 and the conductor portion 131A and RTD mesa 142 .

FIG. 16 is a planar structure and an equivalent circuit diagram of the terahertz oscillator 100, and FIG. 17 is an equivalent circuit diagram of the oscillating state. That is, the equivalent circuit of the terahertz oscillator 100 is shown in _FIG . 16, and the bias voltage Vb from the bias pads 110 and 111 is composed of the line inductance _{LW, the circulating current inductance L S of} the split ring resonator 130, and the coplanar strip line. Applied to RTD 140 through inductance L _d and capacitance C _d of 121 , stabilizing resistors 122 and 123 (both total resistance R _S ) are connected in parallel to RTD 140 . A terahertz wave is radiated via a radiation conductance G _ant . In an oscillating equivalent circuit, the impedance of the inductance _LW increases and the bias circuit is cut off. Further, since the oscillation frequency is mainly determined by the split ring resonator 130, the inductance _Ld and the capacitance _Cd of the coplanar strip line 121 can be omitted, resulting in an equivalent circuit as shown in FIG. That is, if the oscillation frequency of the oscillator is fOSC, the angular frequency ω is ω= _2πf , and the oscillation frequency is expressed by the following equation (5).

ＲＴＤ１４０は例えばAlAs/InGaAsの２重障壁であり、上から下に、n+InGaAs (４×10¹⁹cm^‐3,24nm)/spacer InGaAs (undoped,20nm)/barrier AlAs (undoped,1.2nm)/well InGaAs (undoped,3nm)/barrier AlAs (undoped,1.2nm)/spacer InAlGaAs (undoped,5nm) /n-InAlGaAs (3×10¹⁸cm^‐3,20nm)/n+ InGaAs (４×10¹⁹cm^‐3,5nm)/etch stopper n+InP (４×10¹⁹cm^‐3,10nm)/ n+InGaAs (４×10¹⁹cm^‐3,400nm)/の各層で構成されていても良い。

RTD 140 is, for example, an AlAs/InGaAs double barrier, n+InGaAs (4×10 ¹⁹ cm ⁻³ ,24 nm)/spacer InGaAs (undoped, 20 nm)/barrier AlAs (undoped, 1.2 nm)/ well InGaAs (undoped,3nm)/barrier AlAs (undoped,1.2nm)/spacer InAlGaAs (undoped,5nm)/n-InAlGaAs (3×10 ¹⁸ cm ^‐3 ,20nm)/n+ InGaAs (4×10 ¹⁹ cm ^‐3 , 5 nm)/etch stopper n+InP (4×10 ¹⁹ cm ⁻³ , 10 nm)/n+InGaAs (4×10 ¹⁹ cm ⁻³ , 400 nm)/.

Note that the dimensions and sizes shown in this example are examples, and can be changed as appropriate.

The terahertz oscillator 100 of the present invention integrates the RTD 140 in the center of the split ring resonator 130 and the electric field concentrates in the center of the split ring resonator 130 . Because the terahertz oscillator 100 of the present invention is well confined, it has low losses compared to slot oscillators. FIG. 18 compares the terahertz oscillator 100 of the present invention with the slot oscillator and shows frequency characteristics of conductance and loss. Conductance and loss are directly proportional to each other, and the greater the conductance, the greater the loss. Then, the precondition for oscillation is as shown in Equation 1, and when the absolute value of the negative conductance of the RTD is greater than the conductance of the resonator, the terahertz wave can be oscillated.

The calculated electric field distribution of the terahertz oscillator 100 of the present invention is as shown in FIG. 19(A), which is concentrated in the center of the split ring resonator 130 compared to the slot resonator shown in FIG. 19(B).

FIG. 20 shows the frequency characteristics of the split ring resonator 130 forming the terahertz oscillator 100 of the present invention, and the oscillation frequency is 1 THz or more compared to the case of the slot resonator. The reason why the output drops around 0.5 to 0.9 THz is that the dimensions of the coplanar strip line 121 cause a mismatch with the RTD 140 .

FIG. 21 shows the radiation efficiency (%) based on the length d of the coplanar strip lines 120 and 121 shown in FIG. . Note that the length d is the length from the end face of the coplanar strip lines 120 and 121 to the stabilizing resistor 122 (or from the opposite end face to the stabilizing resistor 123). It becomes a CPS antenna according to.

FIG. 22 shows the relationship between the size [μm ² ] of the RTD mesa 142 and the oscillation frequency. The split ring resonator 130 has a small loss and is capable of oscillation up to around 1.4 THz. In contrast, the slot resonator oscillates up to about 0.9 THz. Jp, ΔV, and PVCR in FIG. 22 are RTD parameters, which can be extracted from the voltage-current characteristics of the RTD 140 . Jp is the current density (peak current/mesa size), ΔV is the voltage difference between the peak point and the valley point, and PVCR is the current ratio between the peak point and the valley point.

23 to 26 show various characteristic examples comparing the case with a CPS antenna (d=26.5 μm) and the case without a CPS antenna (d=0), and FIG. FIG. 24 shows the relationship between the conductance [S] and FIG. 24 shows the relationship between the size [μm ² ] of the RTD mesa 142 and the oscillation frequency [THz]. From this, it can be seen that the metal loss due to the bias electrode can be reduced by adjusting the CPS antenna in the frequency range of 0.8 THz or higher. That is, in the frequency range of 0.8 THz or higher, the CPS line functions as an antenna to radiate the generated terahertz waves into space via the CPS line. Therefore, the conductor loss of the stabilizing resistor and the metal loss of the bias pad can be reduced.

Also, by providing the CPS antenna, the limit of the RTD oscillation frequency is increased from 1.1 THz to 1.4 THz. FIG. 25 shows the relationship between frequency [THz] and radiation efficiency [%], and FIG. 26 shows the relationship between oscillation frequency [THz] and output power [μW]. From this, it can be seen that the metal loss due to the bias pad can be reduced by radiation of the CPS antenna in the frequency range of 0.8 THz or higher. Radiation efficiency can be increased due to the reduction of ballast resistor conductor loss and bias pad metal loss. Note that the radiation efficiency is defined by Equation 6 below.
(Number 6)
Radiation efficiency = radiation power / (radiation power + loss power)

Also, from FIG. 26, the output power of the RTD can be increased by providing the CPS antenna.

FIG. 27 is a plan view of an actually fabricated terahertz oscillator, in which residue of n+InGaAs adheres inside the split ring resonator 130 . FIG. 28 shows the relationship between the oscillation frequency of the RTD mesa 142 when the residue is removed and when the residue is present. can do.

FIG. 29 shows a connection example of a large-scale array 200 using a large number of terahertz oscillators 100 of the present invention. 201 is connected with arm pieces 201-1, 201-2 and 201-3, and the DC/AC pad 202 is connected with arm pieces 202-1, 202-2 and 203-3. Terahertz oscillators 100-1 to 100-4 are connected in parallel between arm piece 201-1 and arm piece 202-1, and terahertz oscillators are connected between arm piece 201-2 and arm piece 202-2. 100-11 to 100-14 are connected in parallel, and terahertz oscillators 100-21 to 100-24 are connected in parallel between the arm pieces 201-3 and 202-3. In the example of FIG. 29, 12 terahertz oscillators 100 are connected in three stages, but more terahertz oscillators 100 can be connected.

Such large-scale arrays 200 can be applied to high-speed modulators, high-sensitivity sensors, high-power arrays, and the like.

FIG. 30 shows an example of a high speed modulator, with a modulation source 210 connected between DC/AC pads 201 and 202 as shown in FIG. 30(B). Then, when a terahertz wave with a time function as shown in FIG. 30(A) is applied as a carrier signal to the front surface of the large-scale array 200, a modulated signal as shown in FIG. 21(C) is output from the rear surface. . If a carrier signal of several hundred GHz is modulated at several tens of GHz, application to 5G and 6G generation communications is possible.

FIG. 31 shows an example of a highly sensitive sensor, in which a DC power supply 220 is connected between DC/AC pads 201 and 202 as shown in FIG. 31(B). Then, when a terahertz wave with a frequency function as shown in FIG. frequency deviation Δf occurs. By measuring the frequency shift Δf, it is possible to analyze the refractive index and thickness of the attached sample 221 to be measured.

Also, FIG. 32(A) shows a configuration example of a high-output array light source, in which a DC power supply 220 is connected between DC/AC pads 201 and 202, and in the case of a single one, FIG. In the case of the large-scale array 200, the output intensity W2 is large as shown in FIG. 32(B).

Industrial field of application

By using the microscopic device of the present invention, it becomes easy to manufacture a compact chip for measuring the absorption spectrum of substances existing in the terahertz frequency band and a light source chip for terahertz imaging, thereby promoting further development in the chemical, medical, and security fields. is considered possible.

1 Resonant tunnel diode (RTD)
2 slot antenna 3 InP substrate 4 lower electrode 5 upper electrodes 6, 13, 14 stabilizing resistor 7 MIM capacitor 10 slot antenna oscillator 11 resonant tunneling diode (RTD)
12 slot antennas 15, 16 electrode plate 17 bias circuit 18 conductive member 100 terahertz oscillator 100A oscillator 101 Sl-InP substrate 102 n+InGaAs layer 103 n+InP layer (etch stopper)
110, 111 bias pads 120, 121 coplanar strip lines 120-1, 120-2 recesses 120A, 121A bias passages 121-1 protrusions 121-1, 121-2 recesses 122, 123 stabilization resistor 130 split ring resonator (SRR )
131 Conductor piece 131A Conductor portion 140 RTD
141 resonant space 142 RTD mesa 200 large scale array 201, 202 DC/AC pads

Claims (6)

A split ring resonator is formed between a first coplanar stripline and a second coplanar stripline to which a bias voltage is applied, and adjacent to the split ring resonator, the first coplanar stripline and the A stabilizing resistor is connected between a second coplanar stripline, a resonant tunneling diode (RTD) is provided on the second coplanar stripline through a mesa, and the first coplanar stripline and the mesa are connected. A conductive strip forming an air bridge is suspended between
A terahertz oscillator characterized by oscillating by resonance of said RTD, said split ring resonator, and said stabilizing resistor. The split ring resonator is
With the recessed space provided in the first coplanar stripline and the two recessed spaces provided in the second coplanar stripline,
2. The terahertz oscillator according to claim 1, wherein the terahertz oscillator is generally U-shaped. 3. The terahertz oscillator according to claim 1, wherein a U-shaped resonant space is provided around the mesa of the second coplanar strip line. 4. The terahertz oscillator according to any one of claims 1 to 3, wherein the tip of said conductive piece is a rectangular conductor portion, and said conductor portion is layered on said mesa. 5. The terahertz band according to claim 1, wherein said first coplanar stripline and said second coplanar stripline are connected to said first bias pad and said second bias pad via bias paths, respectively. oscillator. 6. The terahertz oscillator according to claim 1, wherein said RTD is provided on an n+InP etch stopper of said second coplanar strip line.

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