JP5943411B2 - Field effect transistor - Google Patents

Description

  The present invention relates to a field effect transistor for detecting a measurement object.

  Conventionally, in order to accurately measure a measurement target such as light, heat, or gas, various sensors such as a field effect transistor that can output a large current or voltage even with a slight action with the measurement target have been developed.

  For example, a single-electron transistor that is a kind of field effect transistor in which a bowtie antenna that concentrates millimeter-wave and far-infrared light is arranged on a submicron-sized quantum dot, and an external magnetic field that is applied to the quantum dot Therefore, a millimeter-wave / far-infrared light detector has been developed that has an order of magnitude higher sensitivity than conventional ones and operates at a high speed (for example, see Patent Document 1).

Patent 4029420

  However, in the prior art such as Patent Document 1, an apparatus for generating an external magnetic field is used to control the energy interval between the energy levels of the electrons of the quantum dots together with the bias voltage of the gate electrode by applying an external magnetic field. It is necessary to arrange it separately from the single-electron transistor, which increases the device scale.

  In addition, since measurement objects such as millimeter waves and far-infrared light directly act on the quantum dots, irradiation with millimeter-wave and far-infrared light with a certain level of power increases the temperature of the quantum dots, resulting in poor electrical characteristics. It becomes stable and the detection sensitivity of the measurement object becomes worse.

  In view of the problems of the above-described conventional technology, an object of the present invention is to provide a technology capable of maintaining the detection sensitivity of a measurement object high without increasing the device scale.

One embodiment of a field-effect transistor that exemplifies the present invention includes a semiconductor substrate, a source region and a drain region that are formed over the semiconductor substrate with a space therebetween, and an adjacent source region and drain region with an insulating layer interposed therebetween. Capacitance due to electrostatic coupling between the source region and the drain region , using a gate region formed on the semiconductor substrate and a protrusion disposed so as to protrude toward the region between the source region and the drain region A capacity control unit for controlling

  In addition, a charge island formed in a region between the source region and the drain region and connected to each of the source region and the drain region through a tunnel junction may be provided.

In addition, the capacitance control unit has a protrusion disposed at one end so as to face the region between the source region and the drain region in the vertical direction of the semiconductor substrate surface, and bends in the vertical direction according to the action from the outside. a supporting portion that changes, other end of the support portion is fixed, a distance setting unit for setting a distance to the region between the source region and the drain region from the projections may further comprise a.

  In addition, the capacitance control unit may be disposed in a different housing from the semiconductor substrate including the source region, the drain region, and the gate region.

  In addition, the capacitance control unit may be disposed on the same substrate as the semiconductor substrate including the source region, the drain region, and the gate region.

Another aspect of the field effect transistor illustrating the present invention is a semiconductor substrate, a source region and a drain region formed on the semiconductor substrate with a space therebetween, and adjacent to the source region and the drain region through an insulating layer. And a capacitance control unit that controls capacitance due to electrostatic coupling between the source region and the drain region . The capacitance control unit includes a source region of the semiconductor substrate. A groove portion formed in a region insulated from the drain region and the gate region, and a wire portion which is arranged so as to bridge the groove portion and bends in a direction perpendicular to the semiconductor substrate surface in accordance with an external action to change the capacitance , Ru, further comprising: a.

  An object of the present invention is to maintain a high detection sensitivity of a measurement object without increasing the apparatus scale.

The figure which shows the structural example of the single electron transistor which concerns on one Embodiment of this invention. The figure which expanded the area | region A shown in FIG. Diagram showing an example of Coulomb oscillation by a single electron transistor The figure which shows the equivalent circuit of the single electron transistor shown in FIG. The figure which shows the structural example of the single electron transistor which concerns on the modification of one Embodiment of this invention. The figure which shows the structural example of the single electron transistor which concerns on other embodiment of this invention. The figure which shows the equivalent circuit of the single electron transistor shown in FIG. The figure which shows another example of a structure of the single electron transistor which concerns on one Embodiment of this invention The figure which shows another example of a structure of the single electron transistor which concerns on other embodiment of this invention.

<< One Embodiment >>
FIG. 1 shows a configuration of a single electron transistor which is a kind of field effect transistor according to one embodiment. 1A to 1C are a diagram of a single electron transistor viewed from directly above (Z-axis direction), a diagram viewed from the Y-axis direction, and a cross-sectional view between Y1 and Y2 in FIG. Show. FIG. 2 is an enlarged view of the area A shown in FIG.

The single-electron transistor of the present embodiment has the same structure as a conventional single-electron transistor except for a support column 17, a piezo element 18, and a cantilever 19 which will be described later. That is, in the single electron transistor of this embodiment, the oxide film 16 in which the Si gate region 10 is formed on the oxide film 21 on the silicon (Si) semiconductor substrate 22 on which the SiO ₂ oxide film 21 is formed. It is formed and arranged together with the Si source region 12 and the drain region 14 via the (insulating layer). A gate electrode 11, a source electrode 13, and a drain electrode 15 are formed in the gate region 10, the source region 12, and the drain region 14, respectively. As shown in FIGS. 1 and 2, the single-electron transistor is formed when the Si quantum dots 30 (charge islands) and the quantum dots 30 are formed between the source region 12 and the drain region 14. Tunnel partition walls 31s and 31d, which are Si constricted regions. As a result, the source region 12 and the drain region 14 are tunnel-junction through the quantum dots 30 and the tunnel partition walls 31s and 31d, and as shown by the solid line in FIG. 3, between the source region 12 and the drain region 14, A current Isd that undergoes Coulomb oscillation flows at an interval corresponding to the capacity of the tunnel barriers 31s and 31d.

By the way, as described above, the conventional single-electron transistor acts by directly applying an object to be measured to the quantum dot 30 from the outside, and changing the amount of charge accumulated in the quantum dot 30, thereby changing the peak position of the current Isd and The object to be measured is detected from the amount of change in the current Isd at the predetermined voltage V ₀ . However, when the measurement target is directly applied to the quantum dots 30, the temperature rises or the measurement target adheres, and the peak position and change amount of the current Isd cannot be measured accurately, noise increases, and It becomes unstable and the detection sensitivity deteriorates.

  Therefore, in this embodiment, as shown in FIG. 1, an L-shaped support column 17 is arranged on an oxide film 20 on the same substrate as the semiconductor substrate 22 on which a single electron transistor is formed, and the piezoelectric element 18 and a flat plate A capacity control unit composed of a cantilever 19 having a projection at the tip of the column is disposed on the support column 17. In other words, in the present embodiment, the detection sensitivity is prevented from being lowered by detecting the measurement object by acting on the flat plate of the cantilever 19 without acting on the quantum dot 30 from the outside.

Incidentally, the support 17 of the present embodiment is formed in an L-shape as shown in FIG. 1, is used as the Si surface in such oxide film is an insulating treatment such as SiO _2. However, an insulator or any insulating material and any shape may be used as the support column 17.

  The piezo element 18 (distance setting unit) is disposed on the support column 17 and connected and fixed to one end of the flat plate of the cantilever 19. Furthermore, since the size of the piezo element 18 is several millimeters, the size of the protrusion of the cantilever 19 described later is as small as several micrometers. Therefore, the piezo element 18 of this embodiment includes the cantilever 19. In order to facilitate electrostatic coupling between the protrusions and the quantum dots 30, for example, those having a wedge shape as shown in FIG. The piezo element 18 expands and contracts in accordance with a voltage applied by an external DC power supply (not shown), and sets a predetermined distance between the protrusion at the other end of the cantilever 19 and the quantum dot 30. In other words, the piezo element 18 can set the peak position of the current Isd that undergoes Coulomb oscillation, for example, at the position indicated by the solid line in FIG. In the present embodiment, the piezo element 18 is used as the distance setting unit, but any device that can set the distance between the protrusion of the cantilever 19 and the quantum dot 30 may be used. Further, although the piezo element 18 has a wedge shape, a rectangular shape may be used. In this case, the shape of the flat plate of the cantilever 19 is easily electrostatically coupled to the quantum dots 30. As described above, it is preferable to modify the arrangement appropriately.

  On the other hand, as shown in FIG. 1, the cantilever 19 (supporting portion) is formed in a shape having a flat plate and a protrusion, for example, with silicon nitride, and the surface is coated with a metal such as gold, silver, or aluminum. Use things. Further, the flat plate of the cantilever 19 is formed to have a small spring constant value so that it can be easily bent according to the action of the measurement object from the outside. In addition, it is preferable to shape | mold a projection part in the shape which has a curvature radius equal to or smaller than the magnitude | size of the quantum dot 30 so that it may become easy to carry out electrostatic coupling between the quantum dots 30. FIG. As shown in FIG. 1, the cantilever 19 is arranged such that one end of the flat plate is fixed to the wedge-shaped inclined portion of the piezo element 18 and the protrusion at the other end faces the quantum dot 30 in the Z-axis direction. The

  FIG. 4 shows an equivalent circuit of the single electron transistor of this embodiment. That is, as shown in FIG. 4, the source region 12 and the drain region 14 are tunnel-junction via the quantum dots 30 and the tunnel capacitances Cs and Cd by the tunnel partition walls 31s and 31d. Each of the gate electrode 11 and the cantilever 19 is electrostatically coupled to the quantum dot 30 via the capacitors Cg and Cm. The voltage Vsg is applied between the gate electrode 11 and the source electrode 13, and the constant voltage Vm is applied between the source electrode 13 and the cantilever 19. The energy interval between places is controlled. In the present embodiment, Cs = Cd.

  Next, the operation of the single electron transistor of this embodiment will be described.

In the single-electron transistor of this embodiment, voltages Vsg, Vsd, and Vm are applied between the source electrode 13, the gate electrode 11, the drain electrode 15, and the cantilever 19 by an external DC power source (not shown). At the same time, the protrusion of the cantilever 19 and the quantum dot are applied to the piezoelectric element 18 of the single-electron transistor so that a voltage is applied by another external DC power source (not shown) and the current Isd peaks at a predetermined voltage V _0. Adjust the distance to 30.

The single-electron transistor is made to act on the flat plate of the cantilever 19 with the object to be measured. Due to the action with the object to be measured, the flat plate of the cantilever 19 is bent, and the distance between the protrusion of the cantilever 19 and the quantum dot 30 changes. For example, when the distance between the protrusion of the cantilever 19 and the quantum dot 30 is shortened, the capacity Cm increases. As a result, increases the number of charges accumulated in the quantum dots 30, for example, as indicated by one-dot dashed line in FIG. 3, the peak current Isd deviates from the initial position V ₀ on the left side. On the other hand, when the distance between the protrusion of the cantilever 19 and the quantum dot 30 is increased, the capacitance Cm is decreased and the number of charges accumulated in the quantum dot 30 is decreased. As a result, for example, as shown by the broken line in FIG. 3, the peak current Isd deviates from the initial position V ₀ on the right.

As a result, the user can measure the amount of change in the peak position of the current Isd output from the single-electron transistor, or the amount of change in the current Isd at the initial position V ₀ , whereby the detection of the measurement object and the amount thereof can be known. At this time, the change amount ΔIsd of the current becomes a large value because the gradient ΔIsd / ΔV at the initial position V ₀ is steep, and high sensitivity detection is possible.

  As described above, in this embodiment, the measurement target is acted on the flat plate of the cantilever 19 to bend, thereby preventing the temperature rise of the quantum dots 30 and the adhesion of the measurement target, and increasing the detection sensitivity of the measurement target. Can be maintained.

Moreover, the energy interval between the energy levels of the electrons of the quantum dots 30 can be controlled simply by arranging the piezo element 18 and the cantilever 19 on the support column 17, and the detector can be miniaturized.
<< Modification of one embodiment >>
FIG. 5 shows a configuration of a single electron transistor according to a modification of one embodiment of the present invention. 5A to 5C show a single electron transistor viewed from the Z-axis direction, a diagram viewed from the Y-axis direction, and a cross-sectional view taken along Y3-Y4 in FIG. 5A, respectively. In the single-electron transistor of this embodiment, the same components as those of the single-electron transistor of one embodiment shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The difference between the single-electron transistor of this embodiment and that of the one embodiment is that a capacitance control unit composed of the piezo element 18 and the cantilever 19 is directly disposed on the oxide film 20 of the semiconductor substrate 22. is there.

  On the other hand, the operation of the single-electron transistor of this embodiment is the same as that of the single-electron transistor of one embodiment shown in FIG.

  As described above, in this embodiment, the measurement target is acted on the flat plate of the cantilever 19 to bend, thereby preventing the temperature rise of the quantum dots 30 and the adhesion of the measurement target, and increasing the detection sensitivity of the measurement target. Can be maintained.

Moreover, the energy interval between the energy levels of the electrons of the quantum dots 30 can be controlled only by arranging the piezo element 18 and the cantilever 19, and the detector can be downsized.
<< Other embodiments >>
FIG. 6 shows a configuration of a single electron transistor according to another embodiment. 6A to 6C show a single electron transistor viewed from the Z-axis direction, a diagram viewed from the Y-axis direction, and a cross-sectional view taken along Y5-Y6 in FIG. 6A, respectively. FIG. 7 shows an equivalent circuit of the single-electron transistor of this embodiment. In the single-electron transistor of this embodiment, the same components as those of the single-electron transistor of one embodiment shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof is omitted.

  The difference between the single-electron transistor of this embodiment and the one of the embodiments is that the capacitance control unit bridges the groove 40 formed in a region of the oxide film 20 close to the quantum dot 30 and the groove 40. The wire 50 is arranged in such a manner. Further, no voltage is applied to the wire 50.

  The groove 40 is formed by fine processing such as etching. In addition, it is preferable that the shape, arrangement position, width, depth, and the like of the groove portion 40 are determined according to the required detection sensitivity and measurement accuracy of the measurement target.

  The wire 50 (wire portion) is a conductive wire such as a nanowire or a nanotube that is disposed on the oxide film 20 so as to bridge the groove portion 40 in the Y-axis direction and has a length that reaches a part of the quantum dot 30. . The wire 50 is fixed by van der Waals force. Then, the wire 50 bends when a measurement object is applied to the portion that bridges the groove portion 40 from the outside, and the portion disposed in the quantum dot 30 of the wire 50 becomes Z as shown in FIG. Float in the axial direction. As a result, the capacitance Cm ′ between the wire 50 and the quantum dot 30 shown in FIG. 7 changes. In addition, since the oxide film (not shown) is formed in Si surfaces, such as the gate area | region 10 and the quantum dot 30, the wire 50 and the quantum dot 30 are mutually insulated.

Next, the operation of the single electron transistor of this embodiment will be described. As described above, the wire 50 since no voltage is applied, current Isd before detection is assumed to be obtained beforehand measuring the position V ₀ to be the peak.

In the single-electron transistor of this embodiment, voltages Vsg and Vsd are applied between the source electrode 13, the gate electrode 11, and the drain electrode 15 by an external DC power source (not shown). The single-electron transistor acts by applying a measurement target to a portion of the wire 50 that bridges the groove 40. Due to the action with the object to be measured, the portion of the wire 50 that bridges the groove 40 is bent, and the portion of the wire 50 that is disposed on the quantum dot 30 is lifted in the Z-axis direction. As a result, as shown in FIG. 6C, for example, the distance between the wire 50 and the quantum dot 30 changes. As shown in FIG. 6C, when the distance between the wire 50 and the quantum dot 30 is increased, the capacitance Cm ′ is decreased and the number of charges accumulated in the quantum dot 30 is decreased. As shown by the broken line in FIG. 3, the peak current Isd deviates from the initial position V ₀ on the right.

As a result, the user can measure the amount of change in the peak position of the current Isd output from the single-electron transistor, or the amount of change in the current Isd at the initial position V ₀ , whereby the detection of the measurement object and the amount thereof can be known.

  As described above, in this embodiment, the measurement target is caused to act on the portion of the wire 50 that bridges the groove portion 40 to bend, thereby avoiding an increase in the temperature of the quantum dots 30 or adhesion of the measurement target. The detection sensitivity of the measurement object can be kept high.

Moreover, the energy interval between the energy levels of the electrons of the quantum dot 30 can be controlled only by using the groove 40 and the wire 50, and the detector can be downsized.
<< Additional items of embodiment >>
(1) Although the single electron transistor is used as the field effect transistor in the above embodiment, the present invention is not limited to this, and the present invention can be applied to other field effect transistors.

  (2) In the above-described one embodiment, the protrusion of the cantilever 19 is formed into a shape having a radius of curvature equal to or smaller than the size of the quantum dot 30, but the present invention is not limited to this. For example, the protrusion of the cantilever 19 may have a pointed shape, or a nanowire, a nanotube, or the like may be further disposed at the tip of the protrusion. Thereby, even when the cantilever 19 is bent slightly, the capacitance Cm with the quantum dot 30 can be greatly changed, and the detection sensitivity of the measurement object can be improved.

  (3) In the above-described one embodiment, the piezo element 18 and the cantilever 19 constituting the capacitance control unit are arranged on the support column 17 provided on the semiconductor substrate 22, but the present invention is not limited to this. For example, as shown in FIG. 8, the capacitance control unit may be arranged in a housing that covers the single electron transistor, which is different from the semiconductor substrate 22.

  (4) In the other embodiments described above, the wire 50 is disposed in the groove 40 as the capacity control unit, but the present invention is not limited to this. For example, as shown in FIG. 9, at the same time as forming the groove 40 ', a fine Si wire that bridges the groove 40' may be integrally formed as a wire 50 'by fine processing such as etching.

  From the above detailed description, features and advantages of the embodiments will become apparent. It is intended that the scope of the claims extend to the features and advantages of the embodiments as described above without departing from the spirit and scope of the right. Further, any person having ordinary knowledge in the technical field should be able to easily come up with any improvements and modifications, and there is no intention to limit the scope of the embodiments having the invention to those described above. It is also possible to use appropriate improvements and equivalents within the scope disclosed in.

DESCRIPTION OF SYMBOLS 10 ... Gate region, 11 ... Gate electrode, 12 ... Source region, 13 ... Source electrode, 14 ... Drain region, 15 ... Drain electrode, 16, 20, 21 ... Oxide film, 17 ... Support | pillar, 18 ... Piezo element, 19 ... Cantilever, 22 ... Semiconductor substrate, 30 ... Quantum dot, 31s, 31d ... Tunnel partition, 40 ... Groove, 50 ... Wire

Claims (6)

A semiconductor substrate;
A source region and a drain region formed on the semiconductor substrate at intervals,
A gate region formed on the semiconductor substrate so as to be adjacent to the source region and the drain region via an insulating layer;
A capacitance control unit that controls a capacitance due to electrostatic coupling between the source region and the drain region , using a protrusion disposed so as to protrude toward a region between the source region and the drain region;
A field effect transistor comprising: The field effect transistor according to claim 1.
A field effect transistor comprising a charge island formed in a region between the source region and the drain region and connected to each of the source region and the drain region through a tunnel junction. The field effect transistor according to claim 1 or 2,
The capacity controller is
The protrusion is disposed at one end so as to face the region between the source region and the drain region in the vertical direction of the semiconductor substrate surface, and bends in the vertical direction according to an external action to change the capacitance. A support part to be
The other end of the support portion is fixed, the field effect transistor further comprising a, a distance setting unit for setting a distance to a region between said from the protrusion source region and the drain region. The field effect transistor of claim 3,
The field control transistor according to claim 1, wherein the capacitance control unit is disposed in a housing different from the semiconductor substrate including the source region, the drain region, and the gate region. The field effect transistor of claim 3,
The field control transistor according to claim 1, wherein the capacitance control unit is disposed on the same substrate as the semiconductor substrate including the source region, the drain region, and the gate region. A semiconductor substrate;
A source region and a drain region formed on the semiconductor substrate at intervals,
A gate region formed on the semiconductor substrate so as to be adjacent to the source region and the drain region via an insulating layer;
A capacitance control unit that controls capacitance due to electrostatic coupling between the source region and the drain region,
The capacity controller is
A groove formed in a region insulated from the source region, the drain region, and the gate region of the semiconductor substrate;
A field effect transistor, further comprising: a wire portion that is arranged so as to bridge the groove portion, bends in a direction perpendicular to the surface of the semiconductor substrate according to an external action, and changes the capacitance.

Images