BRPI0722221A2 - Dispositivo de emissão de campo do tipo triodo de alta frequência e processo de sua fabricação. - Google Patents

Description

Dispositivo de emissão de campo do tipo triodo de alta frequência e processo de sua fabricação.

CAMPO DA INVENÇÃO

A presente invenção refere-se, de forma geral, a um dispositivo micro/nanométrico pertencente à família de tubos a vácuo semicondutores para aplicações de alta frequência e, mais especificamente, a um dispositivo de emissão de campo do tipo triodo de alta frequência e um processo de sua fabricação. ANTECEDENTES DA INVENÇÃO

Como se sabe, tecnologia e aplicações na faixa de frequências de THz foram tradicionalmente restritas ao campo de astronomia molecular e espectroscopia química. Avanços recentes dos detectores e fontes de THz abriram o campo para novas aplicações, incluindo segurança doméstica, sistemas de medição (análise de rede, formação de imagens), aplicações médicas e biológicas (caracterização celular, mapeamento térmico e de espectro), caracterização de materiais (sondagem de campos próximos, controle de qualidade na indústria de alimentos e controle de qualidade farmacêutico).

Embora os usos comerciais de fontes e sensores de THz estejam crescendo, esse crescimento é um tanto limitado pela dificuldade de fornecimento de fontes confiáveis de THz1 para as quais a tecnologia tradicional de semicondutores, devido à baixa mobilidade eletrônica, comprovou não ser satisfatória.

Uso de circuitos eletrônicos a vácuo no lugar de tecnologia de semicondutores permite a exploração da propriedade de elétrons de atingirem velocidades mais altas a vácuo que em um material semicondutor e, portanto, de atingirem frequências de operação mais altas (nominalmente de GHz para THz). O princípio geral de trabalho de dispositivos eletrônicos a vácuo baseia-se na interação entre um sinal de RF e um feixe de elétrons gerado; o sinal de RF impõe uma modulação de velocidade aos elétrons do feixe de elétrons, permitindo uma transferência de energia do feixe de elétrons para o sinal de RF.

As limitações acima foram superadas com a introdução de dispositivos de vácuo com um catodo FEA (Field Emission Array), que levou a vantagens significativas, em especial para amplificação de freqüência THz1 permitindo trabalhar em temperatura ambiente, e para alcançar a redução de tamanho para baixo para as micro e dimensões nanométricas. FEA Uma estrutura de fontes de RF foi primeiramente proposto por Charles Spindt (CA Spindt et al. propriedades físicas de filmes finos catodos de emissão de campo com cones de molibdênio, Journal of Applied Physics, vol. 47 de dezembro . 1976, páginas 5248-5263), e é normalmente referido como o catodo Spindt (ou cátodo frio, devido à temperatura baixa). Em particular, os dispositivos catódicos Spindt consistem campo emissor cones metal microusinados ou pontas formadas sobre um substrato condutor, e em contacto com eles ôhmica. Cada emissora tem sua própria abertura concêntricos em um campo de aceleração entre um ânodo e um catodo eletrodos, um eletrodo de porta, também conhecido como grade de controle, é isolada a partir do ânodo e do cátodo e eletrodos emissores por uma camada de dióxido de silício.

Com individual dicas capazes de produzir dezenas de microamperes, matrizes de grandes dimensões pode, teoricamente, produzir emissões grandes densidades de corrente.

Performance of Spindt cathode devices are Iimited by damaging of the emitting tips due to material wear, and for this reason many efforts have 10 been spent worldwide in searching innovative materiais for their production. · In particular, the Spindt structure was much improved by using Carbon Nanotubes (CNTs) as cold cathode emitters (see for example S. lijima, Helical microtubules of graphitic carbon, Nature, 1991, volume 354, pages 56-58, or W. Heer, A. Chatelain, D. ügarte, A carbon nanotube field-emíssion electron source, Science, 1995, volume 270, number 5239, 15 pages 1179-1180) . Carbon nanotubes are perfectly graphitized, cylindrical tubes that can -be produced with diameters ranging- from about 2 to 100 nm, and Iengths of several microns using various manufacturing processes. In particular, CNTs may be rated among the best emitters in nature (see for example J. M. Bonard, J. -P. Salvetat, T. Stockli, L. Forrõ, A. Chatelain, Field emission from carbon nanotubes: perspectives for applications 20 and clues to the emission mechanism, Applied Physics A, 1999, volume 69, pages 245- 254) , and therefore are ideal field emitters in a Spindt-type device; many studies have already- acknowledged their field emission properties (see for example S. Orlanducci, V. Sessa, M. L. Terranova, M. Rossi, D. Manno, Chinese Physics Letters, 2003, volume 367, pages 109-114) .

In this regard, Figure 1 shows a schematic sectional view of

a known Spindt-type cold cathode triode device 1, using CNTs as field emitters. The triode device 1 comprises a cathode structure 2; an anode electrode 3 spaced from the cathode structure 2 by means of lateral spacers 4 ; and a control gate 5 integrated in the cathode structure 2. The cathode structure 2 with the integrated control gate 5, and the 30 anode electrode 3 , are formed separately and then bonded together with the interposition of the lateral spacers 4. The anode electrode 3 is made up of a first conductive substrate functioning as the anode of the triode device, while the cathode structure 2 is a multilayer structure including: a second conductive substrate 7; an insulating Iayer 8 arranged between the second conductive substrate 7 and the control gate 5; a recess 9 formed to 35 penetrate the control gate 5 and the insulating Iayer 8 so as to expose a surface of the second conductive substrate 7; and Spindt-type emitting tips 10 (only one of which is shown in Figure 1, for simplicity of illustration), in particular CNTs, formed in the recess 9 in ohmic contact with the second conductive substrate 7, and functioning as the cathode of the triode device.

During operation, biasing of the control gate 5 allows controlling the flow of electrons generated by the cathode structure 2 towards the anode electrode 3 , at the area corresponding to and surrounding the recess 9; the current thus generated is collected by the portion of the anode electrode 3 that is placed over the control gate 5.

In the triode device 1, a triode (or active) area can thus be defined (denoted with Ia in Figure 1) , including the region at, and closely surrounding, the emitting tips 10 and recess 9, in which electrons are generated and collected; and a triode biasing area Ib1 as the region outside and externai to the triode area Ia1 through which biasing signals are conveyed to the same triode area.

OBJECT AND SUMMARY OF THE INVENTION

The Applicant has noticed that the topographic configuration of known Spindt-type vacuum tube triode devices suffers from an important limitation, due 15 to the Iarge value of parasitic capacitances existing between the control gate and the cathode and anode electrodes . This parasitic capacitance heavily Iimits the operating frequency that this type of device can reach, reducing the cut-off frequency, and making THz applications, even for micron scaled structures, substantially unfeasible.

In particular, known realization of the cold cathode devices 20 envisages the presence of an extended control gate, which overlaps the conductive cathode substrate, thus forming two plates of a parasitic capacitor (denoted with CGC and shown schematically in Figure 1) . In detail, and assuming the control gate and cathode substrate to be modeled as two flat and parallel plates, the value of this parasitic gate-cathode capacitance CGC is given by C = eoer(A/d) , wherein eO is the vacuum 25 permittivity, er is the relative permittivity of the insulating material between the cathode and the control gate, A is the area of overlap, and d is the distance between the cathode and the control gate. The parasitic gate-cathode capacitance CGC is also much Iarger than the capacitance between the control gate and the emitting tip (denoted with CGT in Figure 1)

Moreover, the overlap between the anode electrode and the

control gate generates a further parasitic capacitance, the gate-anode capacitance (denoted with CGA and shown schematically in Figure 1) , that adds up to the overall parasitic capacitance, determining a further degradation of the cut-off frequency of the device.

From the foregoing, it is evident that the operating frequency

of this type of device is heavily dependent on, and strongly limited by, its topographic characteristics .

The main objective of the present invention is thus to provide an innovative topographical configuration for cold cathode vacuum tubes and an innovative manufacturing process, for the aforementioned drawback to be at Ieast in part overcome.

This objective is achieved by the present invention in that it relates to a high frequency triode-type field emission device, and to a related manufacturing process, as defined in the appended claims.

The present invention achieves the aforementioned objective by varying the typical topography of a triode- type field emission device, and particularly by Iimiting the area of overlap between the cathode and anode electrodes and the control 10 gate, thus reducing the value of the overall parasitic capacitance formed therebetween; the overlap between the different conductive surfaces is indeed Iimited to a triode area of the field emission device.

In detail, the control gate, anode and cathode electrodes are composed of a respective strip-shaped conduction Iine Ieading to a respective terminal; 15 the various electrodes overlap only at the triode area (in particular with the terminais thereof, allowing generation and collection of the electron beam) , while the various conduction Iines are so arranged as not to overlap each other outside the same triode area. In more detail, the conduction lines, conducting electrical signals to/from the respective terminais, are inclined, one with respect to each of the other, at a non-zero 20 angle, in particular at an angle of 60° (or 120° , if the complementary angle between any of the two lines is considered) .

The advantages of the proposed structure are particularly significant in cathode array structures where contributions of ali parasitic capacitances add up; in particular, the possibility of realizing Iarge arrays of cold cathode devices without suffering for frequency Iimitation due to parasitic capacitances is one of the key issues of this structure.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, preferred embodiments, which are intended purely by way of example and are not to be construed as limiting, will now be described with reference to the attached drawings (ali not drawn to scale) , wherein:

• Figure 1 shows a schematic cross-sectional view of a known Spindt-type cold cathode triode with a CNT as field emitter, and with parasitic capacitances highlighted;

• Figure 2 is a schematic top view of a high frequency triode-type field emission device according to the present invention;

• Figure 3 is a schematic perspective exploded view of the high frequency triode-type field emission device of Figure 2 ;

• Figure 4 is a cross sectional view of the high frequency triode-type field emission device according to a first embodiment of the present invention; • Figures 5a-5f are perspective views of a semiconductor wafer during successive steps of a process for manufacturing a cathode structure of the high frequency triode-type field emission device, according to the first embodiment of the present invention;

• Figure 6 is a cross sectional view of a high frequency triode-type field emission device according to a second embodiment of the present invention;

• Figure 7 is a variant of the high frequency triode-type field emission device of Figure 6; and

• Figure 8 is a schematic top view of an array of high frequency triode-type field emission devices according to a further embodiment of the present invention.

DETAfLED DESCRfPTION OF PREFERRED EMBODIMENTS OF THE INVENTION.

The following discussion is presented to enable a person skilled in the art to make and use the invention. Various modifications to the embodiments described will be readily apparent to those skilled in the art, and the generic principies herein may be applied to other embodiments and applications without departing from the spirit and scope of the present invention. Thus, the present invention is not intended to be Iimited to the embodiments shown, but is to be accorded the widest scope consistent with the principies and features disclosed herein and defined in the attached claims .

Figures 2 and 3 show respectively a schematic top view and a perspective exploded view of a high-frequency triode-type field emission device 11 according to the present invention and defined as having a "crossbar structure", while Figure 4 shows a cross sectional view of the high frequency triode-type field emission device 11, in accordance with a first embodiment of the present invention.

In detail, according to the first embodiment of the present invention, the high-frequency triode-type field emission device 11 comprises: a multilayered structure integrating a cathode electrode 12 and a control gate (or control grid) electrode 13 ; and an anode electrode 14, that is bonded to this multilayered structure, using vacuum bonding techniques, with lateral spacer 15 in order to maintain electrical isolation therebetween.

In more detail, the cathode electrode 12 is arranged over a substrate, in particular a multilayer substrate 16 including: a thick insulating Iayer 16c, that acts as a support for the whole structure; a conducting Iayer 16a, made of Silicon or other semiconductor or conducting materiais and acting as a ground plane for the device,- and an overlying insulating Iayer 16b, made e.g. of Silicon oxide. The cathode electrode 12 includes a cathode conduction Iine 12a and a cathode terminal 12b, the Iatter having a full disc shape. The cathode conduction Iine 12a has a strip-like shape with a main extension direction along a first direction x, Ieads to the cathode terminal 12b, and crosses it extending from opposite portions thereof along the first direction x; the cathode conduction Iine 12a is- centered with respect to the cathode terminal 12b. An insulating region 17, having the shape of an annulus, is arranged on the multilayer substrate 16 and the cathode electrode 12, and defines a first recess 18, formed therethrough so as to expose a top surface of the cathode terminal 12b. Spindt-type emitting tips 19 (only one of which is shown in Figures 2-4, for simplicity of illustration) , in particular CNTs, are arranged on the exposed top surface of the cathode electrode 12b within the first recess 18.

The control gate electrode 13 is arranged over, and partially overlaps the cathode electrode 12, in particular it overlaps partially the cathode conduction lines 12a at a triode area 11a of the device (which, as previously, is defined as the area at, and closely surrounding., the emitting tips 19 and first recess 18, in which electrons are generated .and collected) . The control gate electrode 13 includes a gate conduction Iine 13a and a gate terminal 13b, the Iatter having a ring or annulus shape with an inner radius , that is e.g. equal to the radius of the cathode terminal 12b. The gate conduction Iine 13a has a strip-like shape with a main extension direction along a second direction y, and leads to the gate terminal 13b, extending from opposite portions thereof along the second direction y, without Crossing it; the gate conduction Iine 13a is centered with respect to the gate terminal 13b. In particular, the first and second directions x, y define skew lines Iying on parallel planes, and the second direction y is oriented by a non zero angle, in particular by an angle of 120° (or 60°, if the complementary angle is considered) with respect to the first direction x (the angle between the two lines being defined as either of the angles between any two lines parallel to them and passing through a same point in space).

The anode electrode 14 is arranged over the cathode electrode 12 and the control gate electrode 13 , and partially overlaps them, in particular at the triode area 11a. The anode electrode 14 is formed on an insulating substrate 20 that is bonded to the multilayered structure integrating the cathode and control gate electrodes, with the interposition of the lateral spacer 15. In particular, the lateral spacer has here an annulus shape and internally defines a second recess 21, that is equal to the first recess 18, and opens to the inside aperture of the gate terminal 13b and the same first recess 18, allowing flow of the generated electrodes towards the anode electrode 14.

In greater detail, the anode electrode’ 14 includes an anode conduction Iine 14a and an anode terminal 14b, the Iatter having a full disc shape with a radius equal to the radius of the cathode terminal 12b. The anode conduction Iine 14a has a strip-like shape with a main extension direction along a third direction z, and extends along the third direction z from opposite portions of the anode terminal 14b, being centered thereto. In particular, the second and third directions y, z are skew lines Iying on parallel planes and the · third direction z is oriented by a non zero angle, in particular by an angle of 120° (or 60°, if the complementary angle is again considered) with respect to the second direction y. Consequently, each of the first, second and third directions x, y, z is oriented by an angle of 60° (120°) with respect to each of the other ones .

From the foregoing description, it follows that overlapping

between the different conductive regions of the triode device, i.e. the cathode, control gate and anode electrodes 12, 13, 14, is Iimited to the triode area 11a thereof, at which electrons are generated and directed from the cathode terminal 12b (and the emitting tips 19) to the anode terminal 14b. In particular, due to the structure spatial orientation, this 10 overlap is Iimited to the cathode and anode terminais 12b, 14b (which fully overlap) , and to a partial overlap between the gate terminal 13b and the cathode and anode conduction lines 12a, 14a. Advantageously1 the cathode, gate and anode conduction lines 12a, 13a, 14a do not overlap each other.

Figures 5a-5f (where same reference numerais designate same elements as ones described before) show successive steps of the process for manufacturing the multilayered structure integrating the cathode and control gate electrodes of the high-frequency triode- type field emission device 11, according to the first embodiment of the present invention.

In detail, Figure 5a, in an initial step of the process, a 20 multilayered substrate 16 is provided, having an insulating Iayer 16b, e.g. a 4-μ.Γη oxide layer, formed by deposition or oxidation on a conducting Iayer 16a, made of Silicon and having a thickness ranging from 2 to 10 pm (the conducting layer 16a acting as the ground plane of the device) ; the conducting layer 16a is realized on a thick insulating layer 16c (made of Silicon dioxide or quartz) .

Next, Figure 5b, a first metal layer is formed, e.g. by

deposition, on the insulating layer 16b; a photoresist pattern (not shown) is defined on the first metal layer, and the same layer is etched to define the cathode electrode 12, having a strip-shaped cathode conduction Iine 12a and a disc-shaped cathode terminal 12b, coupled to the conduction line. Using known techníques, such as for example e-beam 30 Iithography, a photoresist pattern (not shown) is aligned on the multilayered substrate 16 , and a catalyst film (Fe or Ni) is deposited, e.g. by sputtering, and then lifted-off so as "to Ieave only a catalyst region 24 (Figure 5c) on the cathode terminal 12b, in particular at a center portion thereof . The thickness of the catalyst film is in the range of tens of nanometers (e.g. 5-50 nm) .

Using a further alignment, an insulating layer is deposited

e.g. by sputtering, and then lifted-off, for the formation, Figure 5d, of an insulating region 17, having the shape of an annulus surrounding the catalyst region 24. ' The insulating region 17 is designed to insulate the cathode conduction Iine 12a from the control gate terminal. The insulating layer is made of Silicon oxide with a thickness in the range of microns.

Again using a proper alignment, a second metal layer (not shown) , for example of niobium, having a thickness of about 100 nm, is deposited and 5 then Iifted- off, so as to define the control gate electrode 13 (Figure 5e) . In particular, the control gate electrode 13 comprises a gate conduction Iine 13a, inclined at a non-zero angle with respect to the cathode conduction Iine 12a, and a gate terminal 13b, having an annulus shape with an inner opening facing the catalyst region 24. Then, an anodization process is carried out on the gate electrode 13, in order to reduce the current Iosses and 10 to protect the same gate electrode during a subsequent CNT synthesis process. Next, Figure 5f, the structure is submitted to CNTs synthesis in order to obtain (in a per se known manner) Spindt-type emitting tips 19; in particular, CNTs as field emitters are formed on the catalyst region 24.

The multilayered structure formed as described above and 15 the anode electrode 14 are then aligned (taking into account the desired mutual orientation) and bonded together with the interposition of the lateral spacer 15, creating vacuum therebetween. In particular, the anode electrode 14 is first formed on the insulating substrate 20 (which is made e.g. of glass or Silicon oxide), using common patterning techniques, and then the insulating substrate 20 is bonded to the multilayered 20 structure using standard wafer-to-wafer vacuum bonding techniques, such as anodic bonding, glass frit bonding, eutectic bonding, solder bonding, reactive bonding or fusion bonding.

Given that a high quality vacuum is advantageous for ensuring reliable operation of the high-frequency triode-type field emission device 11, a 25 variant of the described process (not shown in the Figures) may envisage the formation of a region containing a suitable reactive material such as Ba, Al, Ti, Zr, V, Fe, commonly known as a getter region. The getter region may allow, when appropriately activated, molecules desorbed during the bonding process to be captured. For a detailed description of the use of getter material to improve vacuum bonding, reference may be made to 30 Douglas R. Sparks, S. Massoud-Ansari, and Nader Najafi, Chip- Level Vacuum Packaging of Micromachines Using NanoGetters, IEEE transactions on advanced packaging, volume 26, number 3, August 2003, pages 277-282, and Yufeng Jin, Zhenfeng Wang, Lei Zhao, Peck Cheng Lim, Jun Wei and Chee Khuen Wong, Zr/V/Fe thick film for vacuum packaging of MEMS, Journal of Micromechanics and 35 Microengineering1 volume 14, 2004, pages 687-692. In a way not shown, this getter region may for example be formed close to the anode electrode 14 inside the second recess 21 (the lateral spacer 15 being arranged so as to Ieave space for the formation of the getter region) . According to a second embodiment of the high- frequency triode-type field emission device 11, the control gate electrode 13 is integrated with the anode electrode 14 , forming a multilayered structure therewith, instead of being integrated with the cathode electrode 12. This different structure has some specific advantages, as discussed in detail in co-pending patent application PCT/IT2006/000883 filed in the name 5 of the same Applicant on 29.12.2006, and in particular may prevent short circuits occurring between the control gate electrode 13 and the emitting tips 19, and further reduce the value of parasitic capacitances . The mutual spatial arrangement of the cathode, control gate and anode electrodes 12, 13, 14 does not change, so that' mutual overlap is still Iimited to the triode area 11a, as previously discussed in detail. Since the 10 second embodiment can be realized with simple modifications of the manufacturing process described for the first embodiment, the related manufacturing process will not be described again. In detail, Figure 6, the anode electrode 14 is in this case formed on the multilayer substrate 16, again including the thick insulating layer 16c, the conducting layer 16a, acting as a ground plane for the device, and the overlying insulating layer 16b in 15 contact with the anode electrode 14. The insulating region 17 is arranged on the multilayer substrate 16 and the anode electrode 14, and defines the first recess 18, exposing a top surface of the anode terminal 14b . The control gate electrode 13 is arranged on the insulating region 17, with the inner opening of the gate terminal 13b open to the first recess 18.

The cathode electrode 12 is patterned on the insulating

substrate 20, and the emitting tips 19 are formed on the exposed top surface of the cathode terminal 12b. The cathode electrode 12 and insulating substrate 20 are then bonded to the multilayer structure integrating the control gate and anode electrodes 13 ,

14 , with the lateral spacers 15 maintaining electrical isolation therebetween. A possible 25 variant of this second embodiment, Figure 7, may provide for the ground plane (conducting layer 16a) to be coupled to the insulating substrate 20; the cathode electrode 12 is in this case patterned on the multilayer structure made by the insulating substrate 20 formed on the conducting layer 16a. The anode electrode 14, which is integrated with the control gate electrode 13, is instead formed on the insulating layer 16b.

Figure 8 shows a further embodiment of the present

invention, envisaging the formation of an array 25 of a Iarge number of high-frequency triode-type field emission devices 11, having the previously described "cross-bar structure".

In detail, the high-frequency triode-type field emission devices 11 of the array 25 are aligned along the first, second and third direction x, y, z. Each of the high-frequency triode-type field emission devices 11 in the array 25 shares its cathode, gate and anode conduction lines 12a, 13a, 14a, with other devices, with which it is aligned along the first, second and third direction x, y, z, respectively. As a result, the devices aligned in the first, second or third direction share a common conduction Iine1 and in particular the cathode, gate or anode conduction Iine 12a, 13a, 14a directed along that direction; the high-frequency triode-type field emission devices 11 are thus arranged in an hexagonal lattice, providing for a regular, rational and compact area occupation.

The advantages of the triode-type field emission device according to the present invention are clear from the foregoing.

In particular, the envisaged cross-bar structure arrangement allows to strongly reduce the parasitic capacitance effects, and to really extend the operating frequency band of the device in the THz frequency range. This is mainly due to the overlap among the different metal surfaces (gate, cathode and anode electrodes) being Iimited to the triode area of the device, while outside the triode area no overlap is provided between these surfaces (and in particular between the various conduction lines)

. Thus11 the value of the overall parasitic capacitance is heavily reduced.

A simple estimation of the maximum overlapping area to achieve a cut-off frequency of at Ieast 1 THz is possible by considering commonly used expressions. In particular, considering a distance of 2 pm between the cathode and gate terminais 12b, 13b, it is possible to estimate that a maximum overlapping area of 20.000 nm2 is requested to yield a cut-off frequency of- 1 THz. An overlapping area with this value can easily be achieved by using an anodic and cathode circular area with a radius in the range of 0.5 pm, the cathode, gate and anode conduction lines 12a, 13a, 14a having a section of e.g. 0.1 μπι. With this arrangement, the estimated parasitic capacitance is in the range of 10~18 F, therefore taking into account a value of transconductance gm in the range of 0.1-50 μβ and a DC gain in the range of 1-500 (see for example W. P. Kang, Y. M. Wong, J. L. Davidson, D.V. Kerns, B. K. Choi1 J.H.Huang and K. F. Galloway, Carbon nanotubes vacuum field emission differential amplifier integrated circuits, Electronics Letters Vol. 42 No. 4, 2006 and Y. M. Wong, W. P. Kang, J. L. Davidson, J. H. Huang, CarJbon nanotuJbes field emission integrated triode amplifier array, Diamond & Related Materials, vol. 15, p. 1990-1993, 2006 ) the cut-off frequency is in the range of THz.

Moreover, the described cross-bar structure, due to the reduced parasitic capacitance, is well suited for the integration of Iarge arrays of field emitter devices in the THz frequency range. In particular, the chosen orientation for the conduction lines of the cathode, gate and anode electrodes 12, 13, 14, and in particular the inclination angle of 120°, allows to achieve a very Iimited overlap area, together with a rational integration of the array and a reduced area occupation, and it is accordingly particularly advantageous.

The realization of the proposed structure is well suited for CNT Spindt cold cathodes, since CNTs can be grown in well defined position by the use of a suitably patterned catalyst.

Furthermore1 integration of the anode and control gate electrodes in a same structure (as shown in Figures 6 and 7) may prove particularly advantageous, in order to further improve the electrical performances of the triode-type field emission device.

Finally, numerous modifications and variants can be made to the triode-type field emission device according to the present invention, ali falling within the scope of the invention, as defined in the appended claims.

In particular, an initial step of the manufacturing process may envisage the provision of a SOI (Silicon On Insulator) multilayerejd substrate; in this_ case, the cathode electrode 12 (according to the first embodiment) , or anode electrode

14 (according to second embodiment) , may be formed by patterning of the Silicon active layer of the SOI substrate, without having to deposit and etch an additional metal layer.

SOI substrates have indeed already demonstrated to be suitable for the synthesis of carbon nanotubes.

Moreover, the internai vertical sides of the control gate electrode 13 could be spaced out from the internai vertical sides of the insulating region

17 (and the inner radius of the control gate electrode 13 thus be higher than the radius of the cathode and anode terminais 12b, 14b) , so as to be covered by the lateral spacers 15 during the bonding process,- this solution may allow a reduction of the Ieakage currents.

A variant of Figure 4 could also be envisaged, corresponding to that of Figure 7, having the conductive layer 16a (the ground plane) coupled to the insulating substrate 20 and not to the insulating layer 16b.

Additionally, it may readily be appreciated that the thickness

of the various Iayers of the device and the various steps of the manufacturing process are only indicative and may be varied according to specific needs. In particular, for sake of simplicity, the description of the manufacturing process has made reference to manufacturing of a single cathode structure; however, the manufacture of an array of 30 cathode structures simply requires the use of modified Iithographical masks in which a same base structure is repeated.

Claims (21)

1. Dispositivo de emissão de campo do tipo triodo (11), particularmente para aplicações em alta frequência, que compreende um eletrodo de cátodo (12), um eletrodo de ânodo (14) espaçado do eletrodo de cátodo (12), um eletrodo de portal de controle (13) disposto entre o mencionado eletrodo de ânodo (14) e o mencionado eletrodo de cátodo (12) e pelo menos uma extremidade de emissão de campo (19); em que os mencionados eletrodos de cátodo (12), portal de controle (13) e ânodo (14) sobrepõem-se em uma área de triodo (11a) na mencionada extremidade de emissão de campo (19) e que são operáveis para cooperar com a mencionada extremidade de emissão de campo (19) para geração de um feixe de elétrons na mencionada área de triodo; caracterizado pelo fato de que os mencionados eletrodos de cátodo (12), portal de controle (13) e ânodo (14) não se sobrepõem para fora da mencionada área de triodo (11a).

2. Dispositivo conforme a reivindicação 1, caracterizado pelo fato de que cada um dentre os mencionados eletrodos de cátodo (12), portal de controle (13) e ânodo (14) possui uma direção de extensão principal ao longo de uma linha correspondente (x, y, z); em que cada uma das mencionadas linhas correspondentes (x, y, z) é inclinada em um ângulo diferente de zero com relação a cada uma das demais.

3. Dispositivo conforme a reivindicação 2, caracterizado pelo fato de que o mencionado ângulo é de cerca de 60°.

4. Método conforme qualquer das reivindicações 1 a 3, caracterizado pelo fato de que os mencionados eletrodos de cátodo (12), portal de controle (13) e ânodo (14) incluem um terminal correspondente (12b, 13b, 14b) disposto na mencionada área de triodo (11a) e uma linha de condução correspondente (12a, 13a, 14a) que se estende a partir do mencionado terminal correspondente para uma área de orientação (11b) fora da mencionada área de triodo (11a) e operável para conduzir sinais elétricos para o mencionado terminal correspondente; em que as linhas de condução (12a, 13a, 14a) dos mencionados eletrodos de cátodo (12), portal de controle (13) e ânodo (14) são dispostas mutuamente de forma a não se sobreporem.

5. Dispositivo conforme a reivindicação 4, caracterizado pelo fato de que as mencionadas linhas de condução (12a, 13a, 14a) dos mencionados eletrodos de cátodo (12), portal de controle (13) e ânodo (14) estendem-se ao longo de uma linha correspondente (x, y, z); em que cada uma das mencionadas linhas correspondentes (x, y, z) é inclinada em um ângulo diferente de zero com relação a cada uma das demais.

6. Dispositivo conforme a reivindicação 5, caracterizado pelo fato de que o mencionado ângulo é de cerca de 60°.

7. Dispositivo conforme qualquer das reivindicações 4 a6, caracterizado pelo fato de que os terminais (12b, 14b) dos mencionados eletrodos de cátodo (12) e ânodo (14) sobrepõem-se na mencionada área de triodo (11a) e o terminal do mencionado eletrodo de portal de controle (13) sobrepõe-se parcialmente às linhas de condução (12a, 14a) dos mencionados eletrodos de cátodo e ânodo na mencionada área de triodo (11a).

8. Dispositivo conforme a reivindicação 7, caracterizado pelo fato de que as mencionadas linhas de condução (12a, 13a, 14a) dos mencionados eletrodos de cátodo (12), portal de controle (13) e ânodo (14) possuem uma forma similar a fita, são conectadas ao mencionado terminal correspondente (12b, 13b, 14b) e estendem-se ao longo de uma linha correspondente (x, y, z) de partes opostas do mencionado terminal correspondente (12b, 13b, 14b).

9. Dispositivo conforme qualquer das reivindicações 7 ou 8, caracterizado pelo fato de que o terminal (12b) do mencionado eletrodo de cátodo (12) possui um formato de disco, é superado pela mencionada extremidade emissora de campo (19) e encontra-se em contato ôhmico com ela; o terminal (13b) do mencionado eletrodo de portal de controle (13) possui uma forma de anel que define um recesso (18) que se abre em direção à mencionada extremidade de emissão de campo (19); e o terminal (14b) do mencionado eletrodo de ânodo (14) possui um formato de disco sobreposto ao mencionado recesso (18) e extremidade emissora de campo (19); em que um raio interno do mencionado eletrodo de portal de controle (13) não é menor que o raio dos mencionados eletrodos de cátodo e ânodo.

10. Dispositivo conforme qualquer das reivindicações anteriores, caracterizado pelo fato de que compreende adicionalmente uma estrutura de cátodo que inclui o mencionado eletrodo de cátodo (12) e uma estrutura de ânodo que inclui o mencionado eletrodo de ânodo (14), em que as mencionadas estruturas de cátodo e de ânodo são formadas separadamente e unidas entre si com a interposição de espaçadores (14); e o mencionado eletrodo de portal de controle (13) é integrado à mencionada estrutura de ânodo.

11. Conjunto (25) de dispositivos de emissão de campo do tipo triodo (11), caracterizado pelo fato de que compreende uma série de dispositivos de emissão de campo do tipo triodo (11), cada qual conforme qualquer das reivindicações anteriores.

12. Conjunto conforme a reivindicação 11, caracterizado pelo fato de que os mencionados eletrodos de cátodo (12), portal de controle (13) e ânodo (14) possuem uma direção principal de extensão ao longo de uma linha correspondente (x, y, z), em que cada uma das mencionadas linhas correspondentes (x, y, z) é inclinada em um ângulo diferente de zero com relação a cada uma das demais, e incluem uma linha de condução correspondente (12a, 13a, 14a) disposta ao longo da mencionada linha correspondente; e em que os mencionados dispositivos de emissão de campo do tipo triodo (11) são alinhados ao longo das mencionadas linhas correspondentes (x, y, z), os dispositivos alinhados ao longo de uma dada linha compartilham uma linha de condução comum (12a, 13a, 14a) e, particularmente, a linha de condução do mencionado eletrodo de cátodo (12), portal de controle (13) ou ânodo é dirigido ao longo da mencionada linha.

13. Conjunto conforme qualquer das reivindicações 11 ou 12, caracterizado pelo fato de que os mencionados dispositivos de emissão de campo do tipo triodo (11) são dispostos em uma treliça hexagonal.

14. Processo de fabricação de um dispositivo de emissão de campo do tipo triodo (11), particularmente para aplicações de alta frequência, que compreende a formação de um eletrodo de cátodo (12), um eletrodo de ânodo (14) espaçado do eletrodo de cátodo (12), um eletrodo de portal de controle (13) disposto entre o mencionado eletrodo de ânodo (14) e o mencionado eletrodo de cátodo (12) e pelo menos uma extremidade de emissão de campo (19); em que os mencionados eletrodos de cátodo (12), portal de controle (13) e ânodo (14) são formados de maneira a sobrepor-se em uma área de triodo (11a) da mencionada extremidade de emissão de campo (19) e são operáveis para cooperar com a mencionada extremidade de emissão de campo (19) para geração de um feixe de elétrons na mencionada área de triodo; caracterizado pelo fato de que a formação inclui a disposição dos mencionados eletrodos de cátodo (12), portal de controle (13) e ânodo (14), de forma a não se sobreporem fora da mencionada área de triodo (11a).

15. Processo conforme a reivindicação 14, caracterizado pelo fato de que a disposição inclui a disposição dos mencionados eletrodos de cátodo (12), portal de controle (13) e ânodo (14) com uma direção principal de extensão ao longo de uma linha correspondente (x, y, z); em que cada uma das mencionadas linhas correspondentes (x, y, z) é inclinada em um ângulo diferente de zero com relação a cada uma das demais.

16. Processo conforme a reivindicação 15, caracterizado pelo fato de que o mencionado ângulo é de cerca de 60°.

17. Processo conforme qualquer das reivindicações 14 a16, caracterizado pelo fato de que a formação dos mencionados eletrodos de cátodo (12), portal de controle (13) e ânodo (14) inclui a formação do seu terminal correspondente (12b, 13b, 14b) na mencionada área de triodo (11a) e sua linha de condução correspondente (12a, 13a, 14a) que se estende do mencionado terminal correspondente para uma área de orientação (11b) fora da mencionada área de triodo (11a), a mencionada linha de condução correspondente é operável para conduzir sinais elétricos para o mencionado terminal correspondente; e em que a disposição inclui a disposição manual das linhas de condução (12a, 13a, 14a) dos mencionados eletrodos de cátodo (12), portal de controle (13) e ânodo (14), de forma que não se sobreponham.

18. Processo conforme a reivindicação 17, caracterizado pelo fato de que a disposição mútua inclui o posicionamento das mencionadas linhas de condução (12a, 13a, 14a) dos mencionados eletrodos de cátodo (12), portal de controle (13) e ânodo (14) ao longo de uma linha correspondente (x, y, z); em que cada uma das mencionadas linhas correspondentes (x, y, z) é inclinada em um ângulo diferente de zero com relação a cada uma das demais.

19. Processo conforme a reivindicação 18, caracterizado pelo fato de que o mencionado ângulo é de cerca de 60°.

20. Processo conforme qualquer das reivindicações 17 a19, caracterizado pelo fato de que a disposição inclui a disposição dos mencionados terminais (12b, 14b) dos mencionados eletrodos de cátodo (12) e de ânodo (14), de forma a sobrepor-se na mencionada área de triodo (11a), e do terminal do mencionado eletrodo de portal de controle (13), de forma a sobrepor-se parcialmente às linhas de condução (12a, 14a) dos mencionados eletrodos de cátodo e de ânodo na mencionada área de triodo.

21. Processo conforme qualquer das reivindicações 14 a20, caracterizado pelo fato de que compreende adicionalmente: formação separada de uma estrutura de cátodo e uma estrutura de ânodo sobre um substrato isolante correspondente (20, 16b), em que a mencionada etapa de formação de uma estrutura de cátodo inclui a formação do mencionado eletrodo de cátodo (12) e a mencionada etapa de formação da mencionada estrutura de ânodo que inclui a formação do mencionado eletrodo de ânodo (14); e união em seguida das mencionadas estruturas de cátodo e de ânodo com a interposição de espaçadores (15); em que a formação do mencionado eletrodo de portal de controle (13) inclui a integração do mencionado eletrodo de portal de controle (13) na mencionada estrutura de ânodo.