Abstract:
A frequency multiplier based on a low dimensional semiconductor structure, including an insulating substrate layer, a semiconductor conducting layer arranged on the surface of the insulating substrate layer, an insulating protective layer arranged on the surface of the semiconductor conducting layer, an insulating carving groove penetrating the semiconductor conducting layer, an inlet electrode arranged on the side surface of the semiconductor conducting layer, and an outlet electrode arranged on the side surface corresponding to the access electrode is provided. The semiconductor conducting layer comprises two two-dimensional, quasi-one-dimensional, or one-dimensional current carrying channels near to and parallel to each other. The frequency multiplier has advantages that the structure is simple, the process is easy to implement, no extra filter circuit needs to be added, dependence on material characteristics is little, and the selection range of materials is wide.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to PCT Application No. PCT/CN2014/073996, having a filing date of Mar. 25, 2014, based on CN 201310144245.7, having a filing date of Apr. 23, 2013, the entire contents of which are hereby incorporated by reference. 
     FIELD OF TECHNOLOGY 
     The following relates to a frequency multiplier based on a low dimensional semiconductor structure, in particular to a frequency multiplier which needs no additional filter circuit and can work at terahertz frequencies at room temperature. 
     BACKGROUND 
     As semiconductor technology is developing continuously, the characteristic lengths of devices have constantly reduced from micron to the current nanometer scale; and, the corresponding material system structures used have also changed from the traditional higher dimensions (three-dimensions) to lower dimensions (two-dimensions, quasi-one-dimension and one-dimension). Devices based on the low dimensional semiconductor structure usually have a simple process, are easy to integrate, and small in stray capacitance, and therefore are taken as an ideal choice for high-frequency devices. 
     Besides, in comparison with the three-dimensional conductive structures, low dimensional conductive structure&#39;s shielding effects on the electric field are greatly reduced, which results in strong electric field distribution around the conductive structure and increased electric field coupling among the conductive structures. Due to this characteristic of the low dimensional conductive structure, a so-called “self-gating effect” appears in the “Y” shaped planar nano-switch (J. Jan-olof and J. Wesström, “Self-Gating Effect in the Electron Y-Branch Switch”, Phys. Rev. Lett. 82, 2564 (1999)). 
     Frequency multiplying technology is always an essential constitutive part of wireless communication and broadcasting technology. With the rapid development of science and technology, frequency multiplying technology is becoming more and more important. At present, various fields such as digital communication, analog communication, radio astronomy, and terahertz science technologies all have huge demands on frequency multiplying technology. Non-linear elements will result in distortion in waveform of the input signals. According to the Fourier transform theory, the frequency ingredients of the output signal will change. This is the well-known physical basis of the generation of frequency multiplication. At present, non-linear frequency multipliers mainly includes two major types: frequency multipliers based on diodes, and those based on field effect transistors. Those frequency multipliers have a common feature that the output signal includes various frequency ingredients, thus additional filter circuits are needed. 
     MIT researchers published the first frequency multiplier which consists of a single field effect transistor and needs no additional filter circuit (H. Wang, D. Nezich, J. Kong and T. Palacios, “Graphene frequency multipliers”, IEEE Electron Device Letters 30, 547 (2009)). This frequency multiplier is also based on the non-linear feature of the field effect transistor, but the material for manufacturing the field effect transistor is not a traditional material, but a novel material with unique electric properties—graphene. The field effect transistor made from this novel material has a special “V” type current-voltage characteristics such that the output signals only contain the second harmonics of the input signal, thus a single graphene field effect transistor can be manufactured into the frequency multiplier without an additional filter circuit. 
     The above publication from the MIT researchers greatly reduces the circuits of the frequency multiplier, however, this invention is based on the unique electric properties of the manufacturing material, which means that this invention is strongly material depended and cannot be achieved by using other material systems. 
     SUMMARY 
     Provided is a frequency multiplier based on a low dimensional semiconductor structure which hardly depends on the material characteristics and needs no additional filter circuit so as to overcome the defects in the prior art. 
     To fulfill the above, the following technical solution is employed: 
     A frequency multiplier based on a low dimensional semiconductor structure, comprising an insulating substrate layer, a semiconductor conducting layer arranged on the surface of the insulating substrate layer, an insulating conducting layer arranged on the surface of the semiconductor conducting layer, an insulating carving groove penetrating the semiconductor conducting layer, an inlet electrode arranged on a side surface of the semiconductor conducting layer and an outlet electrode arranged on the other side surface corresponding to the inlet electrode. The semiconductor conducting layer comprises two two-dimensional, quasi-one-dimensional, or one-dimensional current carrying channels close to and parallel to each other. 
     Furthermore, the space between the two current carrying channels is less than 1 μm. 
     Furthermore, the dielectric constant of the insulating protective layer is higher than that of the semiconductor conducting layer. 
     Furthermore, when the current carrying channels are quasi-one-dimensional, the insulating carving groove comprises a first insulating carving groove and a second insulating carving groove which are symmetrically arranged and a third insulating carving groove arranged between the first insulating carving groove and the second insulating carving groove; one end of the first insulating carving groove, one end of the second insulating carving groove, and one end of the third insulating carving groove respectively extend to a side surface of the conducting layer; the inlet electrode and the outlet electrode are respectively arranged on opposite surfaces of the conducting layer; the said inlet electrode comprises a first inlet electrode arranged on the side surface of the conducting layer area surrounded by the first insulating carving groove and the third insulating carving groove, and the second inlet electrode arranged on the conducting layer area surrounded by the second insulating carving groove and the third insulating carving groove and on the same side of surface where the first inlet electrode is located. 
     Furthermore, the semiconductor conducting layer is of AlGaAs/InGaAs heterojunction, which comprises an InGaAs layer, an AlGaAs layer, and a δ doping area arranged in the AlGaAs layer to result in a two-dimensional electron gas layer between the AlGaAs layer and the InGaAs layer. 
     Furthermore, the semiconductor conducting layer is of AlGaAs/InGaAs heterojunction, which comprises an InGaAs layer, an AlGaAs layer, and a δ doping area arranged in the AlGaN layer to result in a two-dimensional electron gas layer between the AlGaN layer and the GaN layer. 
     Furthermore, the dielectric constant of the third insulating carving groove is higher than that of the semiconductor conducting layer. 
     Furthermore, when the current carrying channels are two-dimensional, an insulating interval layer and a second semiconductor conducting layer are also arranged in turn between the insulating protective layer and the semiconductor conducting layer; the said structure of the frequency multiplier comprises the insulating substrate layer, the semiconductor conducting layer, the insulating interval layer, the second semiconductor conducting layer, and the insulating protective layer in sequence from the bottom to the surface. 
     Furthermore, one end of the semiconductor conducting layer bends and extends to the bottom surface of the insulating substrate layer; one end of the second semiconductor conducting layer bends and extends to the surface of the insulating protective layer; the bending part of the semiconductor conducting layer is opposite to that of the second semiconductor conducting layer; the said inlet electrode comprises the first inlet electrode which is arranged on the bottom surface of the insulating substrate layer and connected with the bending part of the semiconductor conducting layer and the second inlet electrode arranged on the surface of the insulating protective layer and connected with the bending part of the second semiconductor conducting layer; the said outlet electrode is connected with the insulating protective layer, the second semiconductor conducting layer, the insulating interval layer, the semiconductor conducting layer, and the insulation protective layer. 
     The disclosed frequency multiplier has the following beneficial effects:
     1 It is simple in structure, easy for implement of process, and needs no extra filter circuit.   2 It hardly depends on the material characteristics, so the materials can be selected in a wide scope, including various inorganic and organic semiconductors and novel nano-semiconductor materials, carbon nano-tubes, or graphene.   3 It can work at room temperature at a high frequency. Appropriately selected materials can make it work in terahertz frequency region at room temperature.   

    
    
     
       BRIEF DESCRIPTION 
       Some of the embodiments will be described in detail, with reference to the following figures, wherein like designations denote like members, wherein: 
         FIG. 1  is a schematic view of a surface of a frequency multiplier with quasi-one-dimensional current carrying channels in the first embodiment; 
         FIG. 2  is a sectional view taken along line A-A of  FIG. 1 ; 
         FIG. 3  is an output characteristic curve graph under the effect of two high-frequency signals when the current carrying channels are quasi-one-dimensional, obtained in the Monte-Carlo simulation; 
         FIG. 4  is a variation diagram of working characteristic input signals along with the frequency when the current carrying channels are quasi-one-dimensional, obtained in Monte-Carlo simulation; 
         FIG. 5  is a schematic diagram of the surface of a frequency multiplier with two-dimensional current carrying channels in the second embodiment; 
         FIG. 6  is a sectional view taken along line A-A of  FIG. 5 . 
       Marks:  11 —first insulating carving groove;  12 —second insulating carving groove;  13 —third insulating carving groove; 
         14 —first current carrying channel;  15 —second current carrying channel;  16 —first low resistance area; 
         17 —second low resistance area;  18 —third low resistance area; 
         21 —first inlet electrode;  22 —second inlet electrode;  23 —outlet electrode; 
         3 —two-dimensional conducting layer;  31 —AlGaN layer;  32 —GaN layer;  33 —two-dimensional electron gas layer;  311 —doping area; 
         34 —insulating protective layer;  35 —insulating substrate layer; 
         41 —first insulating carving groove;  42 —second insulating carving groove;  43 —first current carrying channel;  44 —second current carrying channel; 
         45 —first low resistance area;  46 —second low resistance area; 
         51 —first inlet electrode;  52 —second inlet electrode;  53 —outlet electrode; 
         61 —insulating substrate layer;  62 —semiconductor conducting layer;  63 —insulating interval layer;  64 —second semiconductor conducting layer; 
         65 —insulating protective layer. 
     
    
    
     DETAILED DESCRIPTION 
     The present invention is described in detail below with reference to the attached drawings and embodiments. The embodiments and description of the present invention is intending to explain the present invention, and do not limit the present invention. 
     Embodiment 1: Referring to  FIG. 1 , this is a top plan view of the frequency multiplier based on a low dimensional semiconductor structure in this embodiment, omitting the insulating protective layer. Thus, a first insulating carving groove  11 , a second insulating carving groove  12 , a third insulating carving groove  13 , a first inlet electrode  21 , a second inlet electrode  22 , and a outlet electrode  23  are visible. The third insulating carving groove  13  is inserted between the first insulating carving groove  11  and the second insulating carving groove  12 . The first insulating carving groove  11  and the second insulating carving groove  12  are arranged in an opposite position. The space between the first insulating carving groove  11  and the third insulating carving groove  13  forms the first current carrying channel  14 ; the space between the second insulating carving groove  12  and the third insulating carving groove  13  forms the second current carrying channel  15 . The area surrounded by the first insulating carving groove  11  and the third insulating carving groove  13  is the first low resistance area  16 ; the area surrounded by the second insulating carving groove  12  and the third insulating carving groove  13  is the second low resistance area  17 ; and the part of the semiconductor conducting layer excluding the first resistance area  16 , the second resistance area  17 , the first current carrying channel  14 , and the second current carrying channel  15 , is the third low resistance area  18 . The insulating carving grooves can be formed by dry etching. The minimum depth requirement of the insulating carving groove is penetrating the two-dimensional conducting layer  3 . 
     The first inlet electrode  21  is arranged on the side surface of the first low resistance area  16 , and the surface of which is perpendicular to the plane where the first current carrying channel  14  is located. The second inlet electrode  22  is arranged on the side surface of the second low resistance area  17 , and the surface of which is perpendicular to the plane where the second current carrying channel  15  is located. The outlet electrode  23  is arranged on a side surface of the third low resistance area  18 , and the side surface is perpendicular to the plane where the first current carrying channel  14  or the second current carrying channel  15  is located. Therefore, the first inlet electrode  21 , the second inlet electrode  22  and the outlet electrode  23  are respectively arranged on the opposite sides of the semiconductor conducting layer. The input signals are respectively input from the first inlet electrode  21  and the second inlet electrode  22 , pass through the first low resistance area  16  and the second low resistance area  17 , the first current carrying channel  14  and the second current carrying channel  15 , and the third low resistance area  18 , and then are output from the outlet electrode  23 . 
     To make sure that the electric characteristics of the frequency multiplier can be adjusted and controlled by the external electric field, the current carrying channels are made from semiconductor materials. Furthermore, in order to utilize the “self-gating effect” to enable the coupling between the current carrying channels, the current carrying channels are employing two-dimensional, quasi-one-dimensional, or one-dimensional structure which is of low dimension. In this embodiment, the semiconductor material employs one-dimensional structure which is of low dimension. Wherein, the first current carrying channel  14  and the second current carrying channel  15  are parallel to each other, at an interval of 100 nm˜1.0 μm. The self-gating effect is an effect of nano scale, referring to that when the current carrying channels get close, the lateral electric field caused by potential difference between the current carrying channels can change the carrying property of the current carriers, whose effect is similar to the role of the gate of a field effect transistor, only the gate does not actually exist. 
     Referring to  FIG. 2 , this is a sectional view taken along line A-A of  FIG. 1 . In this embodiment, the frequency multiplier comprises an insulating substrate layer  35 , a semiconductor conducting layer  3  arranged on the surface of the insulating substrate layer, and an insulating protective layer  34  arranged on the surface of the semiconductor conducting layer. The said first insulating carving groove  11 , the second insulating carving groove  12  and the third insulating carving groove  13  penetrate the semiconductor conducting layer  3 . Furthermore, the dielectric constant of the third insulating carving groove  13  is higher than the dielectric constant of the semiconductor conducting layer  3 . The insulating protective layer  18  has a high dielectric constant, which is higher than that of the semiconductor conducting layer  3 . The insulating material with the high dielectric constant can play the role of strengthening the mutual coupling of the current carrying channels, so a good signal output curve can be obtained even if the space between the current carrying channels is greater than 1 μm. 
     Furthermore, the semiconductor conducting layer is of AlGaN/GaN heterojunction, which comprises an AlGaN layer, a GaN layer and a two-dimensional electron gas layer formed between the AlGaN layer and the GaN layer. The GAN is able to form a two-dimensional electron gas layer due to its self-polarization effect. 
     Furthermore, the semiconductor conducting layer is of AlGaAs/InGaAs heterojunction, which comprises an InGaAs layer, an AlGaAs layer, and a δ doping area arranged in the AlGaAs layer to result in a two-dimensional electron gas layer between the AlGaAs layer and the InGaAs layer. The doping area plays the role of importing the two-dimensional electron gas. 
     Referring to  FIG. 3  and  FIG. 4 , through Monte Carlo simulation, the working characteristics of the frequency multiplier at room temperature can be obtained when the semiconductor conducting layer is of AlGaN/GaN heterojunction structure. In the simulation, the semiconductor conducting layer employs a structure with the following characteristics: the length of the current carrying channels is 400 nm; the width is 50 nm; the width of the insulating carving groove between the current carrying channels is 200 nm; and the dielectric constant is  12 .  FIG. 3  displays the output characteristics of the frequency multiplier by the effect of the two high frequency signals. On condition of t&lt;20 ps, the first inlet electrode  21  and the second inlet electrode  22  both have no signal input, and the output current of the outlet electrode  23  is zero. In this simulation, a sinusoidal AC signal with amplitude of −5V, a period of 2.5 ps corresponding to frequency of 0.4 THz is used as the input signal of the first inlet electrode  21 . When t=20 ps, the above input signals applied to the first inlet electrode  21 , and then the outlet electrode  23  outputs an oscillating current with a period of 2.5 ps. A sinusoidal AC signal with an amplitude of −5V and a period of 2.5 ps is applied to the second inlet electrode when t=26.25 ps, while the outlet electrode  23  outputs an oscillating current with a corresponding frequency of 0.8 THz in a period of 1.25 ps. It can be seen that, by the effect of the two signals both with the frequency of 0.4 THz, the signal with a frequency of 0.8 THz is output, achieving the frequency multiplication. Besides, from  FIG. 3  it can be seen that the time average of the output AC signal is no longer zero, which indicates that the structure in this embodiment can also be used for rectification of the high frequency signals.  FIG. 4  shows the variation of the amplitude of the output frequency multiplying oscillating current along with the input signal frequency, wherein the output signal under the condition when the input signal is 0.1 THz is used as the denominator for normalization. From the simulating results, at room temperature the working cutoff frequency i.e. the frequency of the input signal of the present invention can be obtained, which is approximately 2.5 THz. The output signal is twice the input signal, so the cutoff frequency of the output signal is approximately 5 THz. 
     Embodiment 2: In this embodiment, the semiconductor conducting layer employs the two-dimensional semiconductor material. 
     Referring to  FIG. 5 , this is a schematic diagram of the surface of the frequency multiplier with two-dimensional current carrying channels. The first insulating carving groove  41  and the second insulating carving groove  42  are oppositely arranged. The space between the first insulating carving groove  41  and the second insulating carving groove  42  forms the current carrying channels. The first low resistance area  45  is on one side of the first insulating carving groove  41 , the current carrying channels, and the second insulating carving groove  42 , and the second resistance low area  46  is on the other side. The first low resistance area  45  is connected with the second low resistance area  46  through the current carrying channel. Referring to  FIG. 6 , when the current carrying channel is two dimensional, the semiconductor structure of the frequency multiplier comprises the insulating substrate layer  61 , the semiconductor conducting layer  62 , the insulating interval layer  63 , the second semiconductor conducting layer  64  and the insulating protective layer  65  arranged in sequence from the bottom to the surface. The insulating protective layer  65  or the insulating interval layer  63  is made of insulating material with a high dielectric constant, capable of strengthening the mutual coupling between the current carrying channels, so that the space between the channels can be greater than 1 μm while the output signal is not affected. 
     Referring to  FIG. 6 , this is a structural diagram of the two-dimensional frequency multiplier with two-dimensional current carrying channels. In this embodiment, the longitudinal structure of the frequency multiplier comprises, in sequence, the second inlet electrode  52 , the insulating substrate layer  61 , the semiconductor conducting layer  62 , the insulating interval layer  63 , the second semiconductor conducting layer  64 , the insulating protective layer  65  and the first inlet electrode  51  in turn from the bottom up. Besides, on the right side is the outlet electrode  53  connected with the second semiconductor conducting layer  64  and the semiconductor conducting layer  62 . In  FIG. 6 , the dotted line area of the second semiconductor conducting layer  64  is the first current carrying channel  43 ; the dotted line area of the semiconductor conducting layer  62  is the second current carrying channel  44 ; and the width of the insulating interval layer between the two current carrying channels is less than 1 μm. In order to facilitate the manufacturing of the electrodes and reduce the interelectrode capacitance, the left ends of the semiconductor conducting layer  62  and the second semiconductor conducting layer  64  are respectively bent towards the substrate and the device surface. In a top plane view, the device comprises, from the left to the right the first inlet electrode  51 , the first low resistance area  45  connecting the first inlet electrode  51 , the second inlet electrode  52  and the current carrying channel, the first current carrying channel  43 , the second low resistance area  46  connecting the current carrying channel and the inlet electrode  53 , and the outlet electrode  53 . The depth of the first insulating carving groove  41  is required to penetrate the second semiconductor conducting layer  64 , and the depth of the second insulating groove  42  is required to penetrate the semiconductor conducting layer  62 . 
     The technical solutions of the above embodiments of the present invention are described in detail. In this text, specific examples are used to describe the principle and implementation mode of the present invention. The above embodiments are applicable to helping to understand the principle of the embodiments of the present invention. Meanwhile, for those ordinarily skilled in this field, changes may be made in the implementation modes and the application scope according to the embodiments of the present invention. In conclusion, the contents of the Description cannot be regarded as limit to the present invention.