RU2554694C1 - Graphene-based tunnel field effect transistor - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: in a tunnel field effect transistor with an insulated gate containing electrodes of source and drain made of multilayer graphene and located at an insulating substrate in the same plane, and also the gate made of a conducting material and located above the areas of source, tunnel junction and drain, electrodes of source and drain are oriented towards each other crystallographically by an even edge of a zigzag type and separated by a vacuum barrier transparent for charge carriers.

EFFECT: invention expands the inventory of tunnel transistor nanodevices; this device alongside its pronounced switching property has on the current-voltage curve of the source and drain electrodes the area with a negative differential resistance, which allows its functioning as the Gunn diode; the device requires lower voltage at the gate.

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Description

The invention relates to the field of nanoelectronics and, in particular, to active elements based on carbon nanostructures, namely, transistors that realize the effect of controlling electric current, and can be used as a basic switching device and a device with negative differential resistance in the manufacture of digital integrated circuits .

An analog of the invention is an insulated gate tunneling field-effect transistor, proposed in [1]. It is a tunneling field-effect transistor, in which the role of source and drain is played by highly doped silicon, and the gate is located above the region of the tunnel junction. The disadvantage of this device is the limitation of its speed due to the small relative to graphene magnitude of the mobility of charge carriers in silicon.

As a prototype, a device was proposed in [2] and [3], in which graphene plays the role of electrodes, which has charge carrier mobility orders of magnitude greater than that of silicon. A distinctive feature of this device is that the tunnel barrier on graphene is carried out by intercalating the desired region with boron, carbon, and nitrogen compounds having a hexagonal lattice (h-BCN) with different concentrations of these elements. As a result of intercalation, a heterostructure domain is formed having a semiconductor type of conductivity with a band gap of 1 to 5 electron volts (depending on the concentration of elements in the h-BCN compound). This device does not assume a specific orientation of the crystallographic lattice of graphene relative to the tunnel gap. The main disadvantages of this device are the current problems in the manufacturing technology of heterostructure domains of the required sizes and shapes, as well as the relatively high gate voltage required for switching this transistor.

A tunneling transistor with graphene electrodes was also proposed in [4]. It resembles the prototype proposed in [2], [3], however, it is proposed here to form the region of the tunnel barrier by placing a silicon insert in the tunnel gap. The main disadvantage of this device is that at the moment the technological implementation of this operation seems to be little feasible. Also, this transistor requires a relatively large voltage at the gate to perform its switching.

Thus, the tasks that the proposed transistor solves are as follows. Firstly, it expands the arsenal of tunneling transistor nanodevices. Secondly, along with the switching ability, its current-voltage characteristics have a region with negative differential resistance, and for this reason this device can perform the functions of both a transistor and a Gunn diode. Thirdly, for its work, it requires gate voltages lower than in existing analogs. Fourth, the technology for producing a nanogap with crystallographically even edges is currently more achievable than the technology for creating h-BCN domains of the desired shape and the technology for introducing a dielectric insert from silicon oxide.

In the inventive tunneling field effect transistor, the source and drain electrodes are made of monolayer graphene sheets lying on the insulating substrate in the same plane, oriented to each other by a crystallographically even zigzag edge and separated by a tunnel-transparent vacuum barrier for charge carriers. The shutter is made of conductive material located above the source, tunnel passage and drain areas.

Distinctive features of this invention are:

1. The presence of a vacuum tunnel-transparent barrier (nanogaps of the desired width). The vacuum tunnel barrier does not require manipulation with the introduction of a dielectric strip or the creation of a hybrid domain of the correct shape, but can be carried out by the following technological methods:

a) nanolithography using scanning tunneling microscopy;

b) electromigration;

c) local anodic oxidation;

g) nanofabrication using transmission electron microscopy;

e) catalytic nanorecision.

2. Orientation of graphene electrodes with a crystallographically even edge of the zigzag type to each other. Near this edge are concentrated specific electronic edge states, the presence of which is necessary for the functioning of the device.

The combination of these features allows you to achieve the task.

Enumeration of figures.

Figure 1 shows the appearance of the device.

1. - a graphene sheet with a width of at least 10 nm and a length of at least 100 nm

2. - a graphene sheet with a width of at least 10 nm and a length of at least 100 nm

3. - an insulator (for example, silicon oxide)

4. - a shutter made of a conductive material (for example, gold)

5. - ohmic contacts (for example, from titanium), are designed to ensure the connection of the electrodes with an external electrical circuit

6. - source contact

7. - drain contact

Figure 2 presents a schematic diagram of the density of states for the left and right electrodes.

In order to avoid the effects of size quantization, graphene sheets 1 and 2 in FIG. 1 must have a length (size from source to drain) of at least 100 nanometers and a width of at least 10 nm. The thickness of the insulator 3 in figure 1 should be sufficient to avoid the tunneling current between the sheets 1 and 2 in figure 1 and the shutter 4 in figure 1 (several times the width of the tunnel gap). The graphene sheets are connected to the external circuits using ohmic contacts 5 in Fig. 1. The operation of the device can be explained using figure 2.

This figure shows the edge density of states for the left and right contacts, depending on the energy. The region of states filled with electrons is blacked out. The upper part of the black region corresponds to the Fermi level. A partially transparent rectangle denotes a transport window — the energy interval in which directional tunnel transport is possible. Figure 2 (a) corresponds to a state in which the potential difference V between the source (6 in figure 1) and the drain (7 in figure 1) is zero and the voltage V _g at the gate (4 in figure 1) is absent, In this case, the region of the filled edge states of the left electrode corresponds to the region of the filled edge states of the right electrode, electron tunneling is impossible, current does not flow through the structure. After the potential difference is applied to the source and the drain, part of the filled states in the left electrode will correspond to the region of free states in the right electrode, a directed tunneling electron current from the left electrode to the right will appear. Figure 2 (b) shows the band diagram for the potential difference between the source and the drain, at which the maximum value of the tunneling current is observed, since in this case the maximum of occupied states of the left electrode corresponds to the maximum of free states of the right electrode. In this state, the transistor is “open”. A further increase in the potential difference will lead to a divergence of the peaks in the density of states and a drop in current, as illustrated in FIG. 2 (c). This section will be characterized by negative differential resistance.

When a positive potential is applied to the gate electrode (4 in FIG. 1) with respect to the source and the drain, the region of occupied states will increase (the so-called capacitor effect [4]), as illustrated in FIG. 2 (d). When applying the potential difference, the source-drain current in the transistor will be suppressed due to the extremely low density of states in the transport window (figure 2 (e)). In this state, the transistor is “closed”. A further increase in the source-drain potential difference will cause one of the peaks of the density of states to fall into the transport window (as shown in Fig. 2 (f)), the latter, in turn, will lead to a sharp increase (step) in the current between the source and runoff.

Thus, in this device, the process of switching from an “open” to a “closed” state by changing the gate potential, which is the main positive effect of the operation of the transistor, can be carried out. In addition, this device has an additional useful effect, namely, in the current-voltage characteristic of this device there is a region with negative differential resistance, which allows it to perform the function of a Gunn diode.

References

[1] Patent RU 2354002

[2] G. Fiori, A. Betti, S. Bruzzone, and G. Iannaccone, Nano Vol. 6, 2642 (2012)

[3] Patent WO 2013080237 A1

[4] D.A. Lead, B.B. Vyurkov, V.F. Lukichev, A.A. Orlikovsky, A. Burenkov, P. Ochsner, Physics and Technology of Semiconductors, 2013, Volume 47, Issue 2, p. 244

Claims (1)

A graphene-based tunneling field effect transistor with an insulated gate containing source and drain electrodes made of monolayer graphene and lying on the insulating substrate in the same plane, as well as a gate made of conductive material and located above the source, tunnel junction and drain areas, characterized in that the source and drain electrodes are oriented to each other by a crystallographically even edge of the zigzag type and are separated by a tunnel-transparent vacuum barrier for charge carriers.

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