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A multifinger microtriode with carbon nanotubes field emission cathode operating at GHz frequency
This content has been downloaded from IOPscience. Please scroll down to see the full text. 2015 Nanotechnology 26 215204 (http://iopscience.iop.org/0957-4484/26/21/215204) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 131.170.6.51 This content was downloaded on 01/07/2015 at 09:04
Please note that terms and conditions apply.
Nanotechnology Nanotechnology 26 (2015) 215204 (5pp)
doi:10.1088/0957-4484/26/21/215204
A multifinger microtriode with carbon nanotubes field emission cathode operating at GHz frequency G Ulisse1, F Brunetti1, C Ciceroni1, F Gemma2, M Dispenza2, A M Fiorello2, F Ricci2 and A Di Carlo1 Department of electronic engineering, University of Rome ‘Tor Vergata’ via del politecnico 1, 00133, Rome, Italy 2 SELEX-ES SpA Via Tiburtina Km 12,4 00131, Rome, Italy 1
E-mail: [email protected] Received 2 March 2015, revised 31 March 2015 Accepted for publication 8 April 2015 Published 7 May 2015 Abstract
Vacuum microelectronic devices play an important role in the field of micro- and nanoelectronics and they have been strongly developed in recent decades. Vacuum microelectronics are mainly based on the field emission effect and the employment of electrons in vacuum in a device with dimensions from tenths to hundredths of a micrometer. In this work, we present the development of a carbon-nanotube-based multifinger microtriode operating from 0.5 to 2 GHz. In this frequency range, a minimum RF signal gain of 5 dB is achieved. Such a device represents an optimized alternative to the standard Spindt-type microtriode. The advantage of such multifinger architecture consists in the possibility to reduce the cathode-grid capacitance by reducing the overlap between the two electrodes using a parallel patterning. This approach allows increasing the cut-off frequency of the devices with respect to the Spindt-type triode. We realized a prototype of the multifinger triode and the field emission properties have been characterized. The frequency behavior has been measured, demonstrating the possibility to amplify RF signal. Keywords: field emission, carbon nanotube, microwave amplifier, cold cathodes (Some figures may appear in colour only in the online journal) 1. Introduction
demonstrated [10, 11]. Vacuum electronic devices can replace solid-state devices when high power, high frequency, and radiation-resistant applications are necessary [12]. In particular, for vacuum microwave triodes, the replacement of thermionic cathodes with cold cathodes that operate at room temperature lead to smaller devices with longer lifetimes [13]. The prototypes of vacuum electron devices based on field emission demonstrated many years ago by Charles Spindt realized a compact triode amplifier with field emitting cathodes based on molybdenum nanocones [14]. However, the realized amplifier did not overcome 1 GHz operating frequency, mainly limited by the cathodegrid capacitance [15]. After the CNTs discovery, several works reported Spindt triodes realized with CNTs instead of molybdenum emitters, but only in 2007 was a CNT-based amplifier operating in the GHz range reported [16]. The realized device
In recent years, strong efforts have been made in the field of carbon-based electronics [1] as a possible alternative to silicon. Important results on carbon nanotube (CNT) devices have been obtained; just a few months ago, a complete computer was realized using only CNT transistors [2]. CNTs have shown very interesting characteristics, such as high electrical and thermal conductivity and good chemical stability [3]. In this context, several CNT-based devices have been realized, including radiofrequency transistors [4, 5], x-ray sources [6], and field emission displays [7]. In particular, CNTs have been extensively studied for their excellent field emission properties and the possibility to realize vacuum devices [8], such as triode amplifiers working at low frequency [9] or electron guns for vacuum tubes, has been 0957-4484/15/215204+05$33.00
1
© 2015 IOP Publishing Ltd Printed in the UK
G Ulisse et al
Nanotechnology 26 (2015) 215204
Figure 1. (a), (b) New multifinger triode geometry and (c) lateral and (d) front view of the multifinger triode.
dielectric layer is present between the cathode and the grid line; for clarity, in figure 1(b), the dielectric between the cathode and the grid is transparent. The cathode and the grid are located on two different planes. A third electrode, the anode, is used above the multifinger structure to collect the emitted electrons. The main difference between this new microtriode and the Spindt type is the possibility of pattering the cathode line that allows reducing the parasitic capacitance. In figure 1(c), the lateral section of the insulating substrate with the grid and the cathode is shown. The CNT emitters are grown on the cathode lines. To optimize the transconductance of the triode as much as possible, the height of the emitters should be equal to the height of the dielectric between the cathode and grid lines. In figure 1(b), the front view is also shown in order to clearly explain the geometrical characteristics of the multifinger triode. The cathode and the modulating grid were realized on the same insulating substrate with two photolithographic steps. Under the substrate, there is a metal layer used as a ground plane necessary for the transmission of RF signals. The necessity of using an insulating layer that defines areas of grid and cathode allows limiting the effects of the capacitive device. The substrate used is undoped silicon coated with a layer of 1 μm thick silicon oxide. The choice of this substrate depends upon the temperature of the CNTs synthesis process that varies in the range of 650–800 °C. The lateral dimension of the substrate is 8 mm and, according to the specifications of the final packaging, the thickness of the substrate is of about 300 μm. The cathode lines are located in a recess on a different plane with respect
however was not an integrated and compact structure; it had large dimensions and a complex architecture formed from several grids, resonant cavities, and input/output waveguides. In previous papers we presented the theoretical study of an innovative architecture, namely crossbar [17, 18], that allowed us to reduce the cathode-grid capacitance, respect to a Spindt triode, and consequently increase the cut-off frequency. This device however presents many technological difficulties such as the realization of the small dimensions of the conductive lines (in the range of hundreds of nanometers), the alignment of the different layers, and the deposition of some micron thick insulating films. In this work, we propose the realization and the characterization of a new architecture for nano-vacuum triodes, the multifinger triode [19], that overcomes the technological limitation of the crossbar structure for which it is necessary to realize aligned nanometric conductive lines and the deposition and etching of several micron thick insulating films. The devices realized on a micrometric scale can amplify the RF signal from a frequency of 0.5 up to 2 GHz. In this frequency range, a minimum gain of 5 dB up to a maximum of 12 dB was achieved. However, this structure allows an easy scaling down of the process, allowing us to reach higher operating frequencies.
2. Realization and characterization The new multifinger structure is shown in figure 1. In this architecture, the cathode and the grid are a metallic stripline that can be patterned, allowing us to reduce their overlap. A 2
G Ulisse et al
Nanotechnology 26 (2015) 215204
Figure 2. (a) Top view of the multifinger active area and (b) top view of the realized structure.
Figure 3. (a) SEM images after the synthesis of the CNTs on the multifinger cathode lines and (b) confocal optical microscope image.
shown. In the inset of figure 3(a), a detail of the CNTs on the cathode line is shown. We also used a confocal optical microscope, as shown in figure 3(b), to verify the CNTs are not higher than the grid lines. The realized multifinger triode has been mounted on a sample holder as shown in figure 4(a). Two SMA connectors are used to electrically connect the cathode and the grid lines to the measurements setup. The sample holder has then been mounted (see figure 4(b)) and measured in a vacuum chamber that can reach a vacuum of 10−7 mbar. The anode is mounted on a motorized stage that can move on the z-axis, allowing changing the cathode-anode distance. In this case, the measurements have been performed maintaining the anode cathode distance fixed at 300 μm. In the vacuum field emission setup, a programmable high voltage source is used to apply voltage on the anode up to 5 kV. The emitted current is measured with a picoammeter, electrically connected to the cathode, with measurements ranging from 2 nA to 20 mA. A 220 kΩ resistance is used in order to protect the picoammeter from high voltage discharge. The modulating grid is connected to a voltage source that can reach up to 500 V. The current losses on the grid are measured with a picoammeter with the same characteristics as the
to the grid lines. The depth of this recess is 0.5 μm (figure 1(d)). In figure 2(a), the top view of the active part of the triode formed from the substrate with the cathode and the grid is shown. Different widths of the fingers have been considered; they varied from 5 to 20 μm. Also, the distance between fingers has been varied from 5 to 10 μm. The best performing devices are the ones with lower finger width and distance between them of 5 μm. In this case, we expect a device operating in the range of few GHz. The connection lines have a width of 50 μm in order to externally connect the device via wire bonding. In figure 2(b), an optical microscope image of a realized multifinger triode is shown. A last lithographic step is performed to define the catalyst areas on the cathode lines where the CNTs are grown. A 5 nm thick film of nickel catalyst is then deposited with thermal evaporation. After this last step, the CNTs are synthesized using a thermal chemical vapor deposition reactor on lithographically patterned nickel. Deposits constituted by multiwall CNTs (MWCNTs) with 50 nm average diameter and about 1 μm high were produced. The presence of CNT was detected with Raman analysis and SEM investigation. In figure 3(a), the multifinger triode after the CNTs synthesis is 3
G Ulisse et al
Nanotechnology 26 (2015) 215204
Figure 4. (a) Multifinger mounted on the sample holder and (b) the device mounted in the vacuum chamber.
Figure 5. (a) DC trans-characteristics and (b) frequency gain of multifinger triode.
one previously described. The trans-characteristics as a function of the voltage applied on the modulating grid of the device are shown in figure 5(a). The grid voltage has been varied from 0 to 20 V showing a modulation effect at low voltages. The anode voltage has been varied from 2600 to 3400 V permitting us to increase the total emitting current. The applied anode voltages could seem quite high for field emission measurements; however, considering the cathodeanode distance of 300 μm, we can note that the maximum applied electric field is only 11.3 V μm−1. These measurements demonstrate that the realized multifinger has a clear grid modulation effect on the emitted current from the CNT cathode. Once the DC characteristics were measured, we also investigated the frequency behavior of the multifinger microtriode. The measurements were carried out using a VNA of Anritsu model MS2024. This tool allows measuring the scattering parameters up to a maximum frequency of 4 GHz. The two ports of the VNA are connected respectively to the grid and the cathode of the multifinger. A bias tee is used for the polarization of the grid. A further bias tee is used in output (cathode line) for the DC current on the cathode. The S21 scattering parameters (power gain) were measured for two current emissions at 100 and 200 μA. The gain of the multifinger turned on is shown in figure 5(b). As shown in the graph in figure 5(b), the increase of the current led to a higher gain due to an increase of the
trasconductance. A gain between 0.5 and 2 GHz greater than 5 dB has been obtained with a maximum gain of 12.5 dB at a frequency of 1.73 GHz. The reduction of the cathode-grid capacitance obtained with the new triode architecture permitted us to work at higher frequencies with respect to the standard Spindt-type triodes [15]. This device represents the first measured compact triode, based on the cold cathode, that overcomes the frequency operation of 1 GHz.
3. Conclusion In summary, we realized a new architecture of the vacuum microtriode based on CNT field emitters. The new geometry permits us to reduce the cathode-grid capacitance, allowing the increase of the operating frequency of the triode amplifier. The device was realized using a standard lithographic process and micromachining techniques such as wet etching and sputtering deposition. CNTs have been grown on cathode lines using a thermal CVD process. The field emission DC characteristics have been measured in a vacuum environment and they have been reported showing the working of the device in the triode configuration. In the DC characterization, a maximum current of 120 μA and a transconductance over 5 μS have been obtained. Furthermore, we demonstrated the possibility to amplify RF signals up to a frequency of 2 GHz with a minimum gain 4
G Ulisse et al
Nanotechnology 26 (2015) 215204
of 5 dB for an emitting current of 200 μA. This work demonstrated the great potential of the multifinger microtriode for the realization of compact vacuum power RF amplifiers.
[10] André F, Ponard P, Rozier Y, Bourat C, Gangloff L and Xavier S 2010 IEEE Int. Vac. Electron. Conf. IVEC 2010 pp 83–4 [11] Ulisse G, Ciceroni C, Brunetti F and Di Carlo A 2014 IEEE Trans. Electron Devices 61 2558–63 [12] Manohara H M, Siegel P H, Marrese C, Chang B C B and Xu J 2002 3rd IEEE Int. Vac. Electron. Conf. 28–9 [13] Lockwood N P, Cartwright K L, Gensheimer P D, Shiffler D A, D’Aubigny C Y, Walker C K, Young A, Fairchild S B and Maruyama B 2010 IEEE Int. Vac. Electron. Conf. IVEC 2010 pp 25–6 [14] Spindt C A 1968 A thin film field emission cathode J. Appl. Phys. 39 3504 [15] Spindt C A, Holland C E, Rosengreen A and Brodie I 1993 J. Vac. Sci. Technol. B 11 468–73 [16] Minoux E et al 2007 Proc. 7th IEEE Int. Conf. on Nanotechnology IEEE-NANO 2007 pp 1248–51 [17] Di Carlo C, Paoloni E, Petrolati F and Brunetti R Riccitelli. High frequency triode-type field emission device and process for manufacturing the same US Patent Specification 8,629,609 [18] Ulisse G, Brunetti F, Ricci F, Fiorello A M and Di Carlo A 2012 IEEE Electron Device Lett. 33 1318–20 [19] Ulisse G, Brunetti F, Di Carlo A, Ricci F, Gemma F, Fiorello A M, Dispenza M and Buttiglione R Electronemitting cold cathode device US Patent Specification 20,150,022,076
References [1] Brosseau C 2011 Surf. Coat. Technol. 206 753–8 [2] Shulaker M M, Hills G, Patil N, Wei H, Chen H-Y, Wong H-S P and Mitra S 2013 Nature 501 526 [3] De Volder M F L, Tawfick S H, Baughman R H and Hart A J 2013 Science 80 535 [4] Li S, Yu Z, Yen S F, Tang W C and Burke P J 2004 Nano Lett. 4 753 [5] Che Y, Lin Y C, Kim P and Zhou C 2013 ACS Nano 7 4343 [6] Jeong J W, Kim J-W, Kang J T, Choi S, Ahn S and Song Y H 2013 Nanotechnology 24 085201 [7] Liu P, Wei Y, Liu K, Liu L, Jiang K and Fan S 2012 Nano Lett. 12 2391 [8] Sun Y, Yeow J T W and Jaffray D A 2012 Small 9 3385 [9] Wong Y M, Kang W P, Davidson J L, Choi B K, Hofmeister W and Huang J H 2005 Diam. Relat. Mater. 14 2069–73
5
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My IOPscience
A multifinger microtriode with carbon nanotubes field emission cathode operating at GHz frequency
This content has been downloaded from IOPscience. Please scroll down to see the full text. 2015 Nanotechnology 26 215204 (http://iopscience.iop.org/0957-4484/26/21/215204) View the table of contents for this issue, or go to the journal homepage for more
Download details: IP Address: 131.170.6.51 This content was downloaded on 01/07/2015 at 09:04
Please note that terms and conditions apply.
Nanotechnology Nanotechnology 26 (2015) 215204 (5pp)
doi:10.1088/0957-4484/26/21/215204
A multifinger microtriode with carbon nanotubes field emission cathode operating at GHz frequency G Ulisse1, F Brunetti1, C Ciceroni1, F Gemma2, M Dispenza2, A M Fiorello2, F Ricci2 and A Di Carlo1 Department of electronic engineering, University of Rome ‘Tor Vergata’ via del politecnico 1, 00133, Rome, Italy 2 SELEX-ES SpA Via Tiburtina Km 12,4 00131, Rome, Italy 1
E-mail: [email protected] Received 2 March 2015, revised 31 March 2015 Accepted for publication 8 April 2015 Published 7 May 2015 Abstract
Vacuum microelectronic devices play an important role in the field of micro- and nanoelectronics and they have been strongly developed in recent decades. Vacuum microelectronics are mainly based on the field emission effect and the employment of electrons in vacuum in a device with dimensions from tenths to hundredths of a micrometer. In this work, we present the development of a carbon-nanotube-based multifinger microtriode operating from 0.5 to 2 GHz. In this frequency range, a minimum RF signal gain of 5 dB is achieved. Such a device represents an optimized alternative to the standard Spindt-type microtriode. The advantage of such multifinger architecture consists in the possibility to reduce the cathode-grid capacitance by reducing the overlap between the two electrodes using a parallel patterning. This approach allows increasing the cut-off frequency of the devices with respect to the Spindt-type triode. We realized a prototype of the multifinger triode and the field emission properties have been characterized. The frequency behavior has been measured, demonstrating the possibility to amplify RF signal. Keywords: field emission, carbon nanotube, microwave amplifier, cold cathodes (Some figures may appear in colour only in the online journal) 1. Introduction
demonstrated [10, 11]. Vacuum electronic devices can replace solid-state devices when high power, high frequency, and radiation-resistant applications are necessary [12]. In particular, for vacuum microwave triodes, the replacement of thermionic cathodes with cold cathodes that operate at room temperature lead to smaller devices with longer lifetimes [13]. The prototypes of vacuum electron devices based on field emission demonstrated many years ago by Charles Spindt realized a compact triode amplifier with field emitting cathodes based on molybdenum nanocones [14]. However, the realized amplifier did not overcome 1 GHz operating frequency, mainly limited by the cathodegrid capacitance [15]. After the CNTs discovery, several works reported Spindt triodes realized with CNTs instead of molybdenum emitters, but only in 2007 was a CNT-based amplifier operating in the GHz range reported [16]. The realized device
In recent years, strong efforts have been made in the field of carbon-based electronics [1] as a possible alternative to silicon. Important results on carbon nanotube (CNT) devices have been obtained; just a few months ago, a complete computer was realized using only CNT transistors [2]. CNTs have shown very interesting characteristics, such as high electrical and thermal conductivity and good chemical stability [3]. In this context, several CNT-based devices have been realized, including radiofrequency transistors [4, 5], x-ray sources [6], and field emission displays [7]. In particular, CNTs have been extensively studied for their excellent field emission properties and the possibility to realize vacuum devices [8], such as triode amplifiers working at low frequency [9] or electron guns for vacuum tubes, has been 0957-4484/15/215204+05$33.00
1
© 2015 IOP Publishing Ltd Printed in the UK
G Ulisse et al
Nanotechnology 26 (2015) 215204
Figure 1. (a), (b) New multifinger triode geometry and (c) lateral and (d) front view of the multifinger triode.
dielectric layer is present between the cathode and the grid line; for clarity, in figure 1(b), the dielectric between the cathode and the grid is transparent. The cathode and the grid are located on two different planes. A third electrode, the anode, is used above the multifinger structure to collect the emitted electrons. The main difference between this new microtriode and the Spindt type is the possibility of pattering the cathode line that allows reducing the parasitic capacitance. In figure 1(c), the lateral section of the insulating substrate with the grid and the cathode is shown. The CNT emitters are grown on the cathode lines. To optimize the transconductance of the triode as much as possible, the height of the emitters should be equal to the height of the dielectric between the cathode and grid lines. In figure 1(b), the front view is also shown in order to clearly explain the geometrical characteristics of the multifinger triode. The cathode and the modulating grid were realized on the same insulating substrate with two photolithographic steps. Under the substrate, there is a metal layer used as a ground plane necessary for the transmission of RF signals. The necessity of using an insulating layer that defines areas of grid and cathode allows limiting the effects of the capacitive device. The substrate used is undoped silicon coated with a layer of 1 μm thick silicon oxide. The choice of this substrate depends upon the temperature of the CNTs synthesis process that varies in the range of 650–800 °C. The lateral dimension of the substrate is 8 mm and, according to the specifications of the final packaging, the thickness of the substrate is of about 300 μm. The cathode lines are located in a recess on a different plane with respect
however was not an integrated and compact structure; it had large dimensions and a complex architecture formed from several grids, resonant cavities, and input/output waveguides. In previous papers we presented the theoretical study of an innovative architecture, namely crossbar [17, 18], that allowed us to reduce the cathode-grid capacitance, respect to a Spindt triode, and consequently increase the cut-off frequency. This device however presents many technological difficulties such as the realization of the small dimensions of the conductive lines (in the range of hundreds of nanometers), the alignment of the different layers, and the deposition of some micron thick insulating films. In this work, we propose the realization and the characterization of a new architecture for nano-vacuum triodes, the multifinger triode [19], that overcomes the technological limitation of the crossbar structure for which it is necessary to realize aligned nanometric conductive lines and the deposition and etching of several micron thick insulating films. The devices realized on a micrometric scale can amplify the RF signal from a frequency of 0.5 up to 2 GHz. In this frequency range, a minimum gain of 5 dB up to a maximum of 12 dB was achieved. However, this structure allows an easy scaling down of the process, allowing us to reach higher operating frequencies.
2. Realization and characterization The new multifinger structure is shown in figure 1. In this architecture, the cathode and the grid are a metallic stripline that can be patterned, allowing us to reduce their overlap. A 2
G Ulisse et al
Nanotechnology 26 (2015) 215204
Figure 2. (a) Top view of the multifinger active area and (b) top view of the realized structure.
Figure 3. (a) SEM images after the synthesis of the CNTs on the multifinger cathode lines and (b) confocal optical microscope image.
shown. In the inset of figure 3(a), a detail of the CNTs on the cathode line is shown. We also used a confocal optical microscope, as shown in figure 3(b), to verify the CNTs are not higher than the grid lines. The realized multifinger triode has been mounted on a sample holder as shown in figure 4(a). Two SMA connectors are used to electrically connect the cathode and the grid lines to the measurements setup. The sample holder has then been mounted (see figure 4(b)) and measured in a vacuum chamber that can reach a vacuum of 10−7 mbar. The anode is mounted on a motorized stage that can move on the z-axis, allowing changing the cathode-anode distance. In this case, the measurements have been performed maintaining the anode cathode distance fixed at 300 μm. In the vacuum field emission setup, a programmable high voltage source is used to apply voltage on the anode up to 5 kV. The emitted current is measured with a picoammeter, electrically connected to the cathode, with measurements ranging from 2 nA to 20 mA. A 220 kΩ resistance is used in order to protect the picoammeter from high voltage discharge. The modulating grid is connected to a voltage source that can reach up to 500 V. The current losses on the grid are measured with a picoammeter with the same characteristics as the
to the grid lines. The depth of this recess is 0.5 μm (figure 1(d)). In figure 2(a), the top view of the active part of the triode formed from the substrate with the cathode and the grid is shown. Different widths of the fingers have been considered; they varied from 5 to 20 μm. Also, the distance between fingers has been varied from 5 to 10 μm. The best performing devices are the ones with lower finger width and distance between them of 5 μm. In this case, we expect a device operating in the range of few GHz. The connection lines have a width of 50 μm in order to externally connect the device via wire bonding. In figure 2(b), an optical microscope image of a realized multifinger triode is shown. A last lithographic step is performed to define the catalyst areas on the cathode lines where the CNTs are grown. A 5 nm thick film of nickel catalyst is then deposited with thermal evaporation. After this last step, the CNTs are synthesized using a thermal chemical vapor deposition reactor on lithographically patterned nickel. Deposits constituted by multiwall CNTs (MWCNTs) with 50 nm average diameter and about 1 μm high were produced. The presence of CNT was detected with Raman analysis and SEM investigation. In figure 3(a), the multifinger triode after the CNTs synthesis is 3
G Ulisse et al
Nanotechnology 26 (2015) 215204
Figure 4. (a) Multifinger mounted on the sample holder and (b) the device mounted in the vacuum chamber.
Figure 5. (a) DC trans-characteristics and (b) frequency gain of multifinger triode.
one previously described. The trans-characteristics as a function of the voltage applied on the modulating grid of the device are shown in figure 5(a). The grid voltage has been varied from 0 to 20 V showing a modulation effect at low voltages. The anode voltage has been varied from 2600 to 3400 V permitting us to increase the total emitting current. The applied anode voltages could seem quite high for field emission measurements; however, considering the cathodeanode distance of 300 μm, we can note that the maximum applied electric field is only 11.3 V μm−1. These measurements demonstrate that the realized multifinger has a clear grid modulation effect on the emitted current from the CNT cathode. Once the DC characteristics were measured, we also investigated the frequency behavior of the multifinger microtriode. The measurements were carried out using a VNA of Anritsu model MS2024. This tool allows measuring the scattering parameters up to a maximum frequency of 4 GHz. The two ports of the VNA are connected respectively to the grid and the cathode of the multifinger. A bias tee is used for the polarization of the grid. A further bias tee is used in output (cathode line) for the DC current on the cathode. The S21 scattering parameters (power gain) were measured for two current emissions at 100 and 200 μA. The gain of the multifinger turned on is shown in figure 5(b). As shown in the graph in figure 5(b), the increase of the current led to a higher gain due to an increase of the
trasconductance. A gain between 0.5 and 2 GHz greater than 5 dB has been obtained with a maximum gain of 12.5 dB at a frequency of 1.73 GHz. The reduction of the cathode-grid capacitance obtained with the new triode architecture permitted us to work at higher frequencies with respect to the standard Spindt-type triodes [15]. This device represents the first measured compact triode, based on the cold cathode, that overcomes the frequency operation of 1 GHz.
3. Conclusion In summary, we realized a new architecture of the vacuum microtriode based on CNT field emitters. The new geometry permits us to reduce the cathode-grid capacitance, allowing the increase of the operating frequency of the triode amplifier. The device was realized using a standard lithographic process and micromachining techniques such as wet etching and sputtering deposition. CNTs have been grown on cathode lines using a thermal CVD process. The field emission DC characteristics have been measured in a vacuum environment and they have been reported showing the working of the device in the triode configuration. In the DC characterization, a maximum current of 120 μA and a transconductance over 5 μS have been obtained. Furthermore, we demonstrated the possibility to amplify RF signals up to a frequency of 2 GHz with a minimum gain 4
G Ulisse et al
Nanotechnology 26 (2015) 215204
of 5 dB for an emitting current of 200 μA. This work demonstrated the great potential of the multifinger microtriode for the realization of compact vacuum power RF amplifiers.
[10] André F, Ponard P, Rozier Y, Bourat C, Gangloff L and Xavier S 2010 IEEE Int. Vac. Electron. Conf. IVEC 2010 pp 83–4 [11] Ulisse G, Ciceroni C, Brunetti F and Di Carlo A 2014 IEEE Trans. Electron Devices 61 2558–63 [12] Manohara H M, Siegel P H, Marrese C, Chang B C B and Xu J 2002 3rd IEEE Int. Vac. Electron. Conf. 28–9 [13] Lockwood N P, Cartwright K L, Gensheimer P D, Shiffler D A, D’Aubigny C Y, Walker C K, Young A, Fairchild S B and Maruyama B 2010 IEEE Int. Vac. Electron. Conf. IVEC 2010 pp 25–6 [14] Spindt C A 1968 A thin film field emission cathode J. Appl. Phys. 39 3504 [15] Spindt C A, Holland C E, Rosengreen A and Brodie I 1993 J. Vac. Sci. Technol. B 11 468–73 [16] Minoux E et al 2007 Proc. 7th IEEE Int. Conf. on Nanotechnology IEEE-NANO 2007 pp 1248–51 [17] Di Carlo C, Paoloni E, Petrolati F and Brunetti R Riccitelli. High frequency triode-type field emission device and process for manufacturing the same US Patent Specification 8,629,609 [18] Ulisse G, Brunetti F, Ricci F, Fiorello A M and Di Carlo A 2012 IEEE Electron Device Lett. 33 1318–20 [19] Ulisse G, Brunetti F, Di Carlo A, Ricci F, Gemma F, Fiorello A M, Dispenza M and Buttiglione R Electronemitting cold cathode device US Patent Specification 20,150,022,076
References [1] Brosseau C 2011 Surf. Coat. Technol. 206 753–8 [2] Shulaker M M, Hills G, Patil N, Wei H, Chen H-Y, Wong H-S P and Mitra S 2013 Nature 501 526 [3] De Volder M F L, Tawfick S H, Baughman R H and Hart A J 2013 Science 80 535 [4] Li S, Yu Z, Yen S F, Tang W C and Burke P J 2004 Nano Lett. 4 753 [5] Che Y, Lin Y C, Kim P and Zhou C 2013 ACS Nano 7 4343 [6] Jeong J W, Kim J-W, Kang J T, Choi S, Ahn S and Song Y H 2013 Nanotechnology 24 085201 [7] Liu P, Wei Y, Liu K, Liu L, Jiang K and Fan S 2012 Nano Lett. 12 2391 [8] Sun Y, Yeow J T W and Jaffray D A 2012 Small 9 3385 [9] Wong Y M, Kang W P, Davidson J L, Choi B K, Hofmeister W and Huang J H 2005 Diam. Relat. Mater. 14 2069–73
5
