Bridge transistor for inducing early saturation of drain current

Abstract

The purpose of the present invention is to propose a new design parameter by which the characteristics of a transistor can be controlled, and at the same time, achieve a reduction in operating voltage and a high gain by lowering the saturation voltage of the transistor. A bridge transistor according to one embodiment comprises: base layers stacked on a substrate and separated from each other in a channel region; electrode layers stacked on the base layers, respectively, and including a source electrode and a drain electrode; and a bridge layer stacked on the channel region and including a material forming at least one junction among a homojunction, a heterojunction, and a Schottky junction with the base layers stacked separated from each other.

Description

Bridge transistors that induce early saturation of drain current

[0001] The present invention relates to the structure of a thin film transistor. A thin film transistor is a type of field effect transistor, and generally has the characteristic that the drain current saturates and becomes constant even when the drain voltage further increases, starting at the moment when the drain voltage becomes equal to the difference between the gate voltage and the threshold voltage. The present invention relates to a structure for reducing the drain voltage at which the drain current saturates to a voltage lower than the difference between the gate voltage and the threshold voltage.

[0002] One of the many directions for transistor development is to lower the operating voltage, which is closely related to power consumption. A transistor has three operating regions: cutoff, linear, and saturation. The cutoff region is the transistor's off state, while the linear and saturation regions are regions where the current increases or remains constant as the drain voltage increases, respectively. The linear and saturation regions are separated by the point where the drain voltage equals the difference between the gate voltage and the threshold voltage.

[0003] Therefore, as the gate voltage increases, the drain voltage at which the saturation region begins also increases proportionally.

[0004] Since most analog circuits operate in the saturation region, lowering the drain voltage at which the saturation region begins can enable low-voltage operation. However, as mentioned earlier, in the case of conventional transistors, the drain voltage at which the saturation region begins is proportional to the gate voltage, and is therefore affected by the gate voltage range used. Therefore, reducing the dependence of the saturation voltage on the gate voltage, thereby bringing forward the point of drain current saturation regardless of the gate voltage, can be a good solution for lowering the operating voltage. This can lead to the implementation of high-gain logic gates not only in analog circuits but also in digital circuits.

[0005] The present invention has been proposed to solve the problems of the above-mentioned prior art, and to achieve a reduction in operating voltage and high gain by lowering the saturation voltage of the transistor while presenting a new design parameter capable of controlling the characteristics of the transistor.

[0006] A bridge transistor according to one embodiment may include a base layer stacked on a substrate and separated from each other by a channel region, an electrode layer stacked on each of the base layers and including a source electrode and a drain electrode, and a bridge layer stacked on the channel region, the bridge layer including a material that forms at least one junction among a homojunction, a heterojunction, or a Schottky junction with the base layers stacked and separated from each other.

[0007] According to one embodiment, a bridge transistor may have materials of the base layer and the bridge layer determined to induce early saturation characteristics of drain current.

[0008] According to one embodiment, the bridge layer may include at least one material selected from the group consisting of p-type organic semiconductors C8-BTBT (C8-Benzothiophene), DNTT (Dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene), Au, and Ni.

[0009] According to one embodiment, the base layer may include C8-BTBT, which is a p-type organic semiconductor, and the bridge layer may include Au.

[0010] According to one embodiment, the base layer may include DNTT, which is a p-type organic semiconductor, and the bridge layer may include Ni.

[0011] According to one embodiment, the base layer may include C8-BTBT, which is a p-type organic semiconductor, and the bridge layer may include DNTT.

[0012] A method for manufacturing a bridge transistor according to an embodiment may include a step of depositing a base layer separated from each other by a channel region on a substrate, a step of depositing a source electrode and a drain electrode laminated on each of the deposited base layers, and a step of depositing a bridge layer on the channel region, wherein the bridge layer forms at least one junction with the base layer among a homojunction, a heterojunction, or a Schottky junction.

[0013] According to one embodiment, the bridge layer may include at least one material selected from the group consisting of p-type organic semiconductors C8-BTBT, DNTT, Au, and Ni.

[0014] In one embodiment, the proposed bridge transistor presents a novel structure that induces an additional junction in the central portion of the channel.

[0015] According to one embodiment, in addition to the structural novelty, unlike a general transistor in terms of electrical characteristics, it can induce saturation of the drain current at a drain voltage close to 0 V, and has the characteristic that the increase in the saturation voltage with respect to an increase in the gate voltage is very small.

[0016] According to one embodiment, the bridge transistor structure with structural novelty and electrical characteristics can be considered as another parameter for controlling the characteristics of the transistor and for device design.

[0017] According to one embodiment, the saturation voltage in the proposed bridge transistor can decrease the saturation voltage in the 0 V direction.

[0018] FIG. 1 is a diagram illustrating a schematic diagram of a bridge transistor according to one embodiment.

[0019] FIG. 2 is a drawing illustrating a manufacturing method of a bridge transistor according to one embodiment.

[0020] Figures 3a to 3d illustrate the transfer curves of a typical P-type transistor.

[0021] Figures 4a to 4d are drawings showing the transfer characteristics and output characteristics of a bridge transistor in which C8-BTBT, a p-type organic semiconductor, is applied as a base region and Au as a bridge layer, and the transfer characteristics and output characteristics of a bridge transistor in which DNTT, a p-type organic semiconductor, is applied as a base region and Ni as a bridge layer.

[0022] Figures 5a to 5d are diagrams showing the output curves of each bridge transistor when the separated C8-BTBT channels are connected to the C8-BTBT, DNTT, and AU bridges, respectively.

[0023] Figures 6a and 6b are diagrams showing the contact resistance or channel resistance of each transistor with respect to the drain voltage (VD) extracted through the G-function method based on the measured output curve.

[0024] Figures 7a to 7f are diagrams showing simulated hole distributions inside the active channel of a transistor based on C8-BTBT, DNTT, and AU bridges.

[0025] Specific structural or functional descriptions of embodiments according to the concept of the present invention disclosed in this specification are merely illustrative for the purpose of explaining embodiments according to the concept of the present invention, and embodiments according to the concept of the present invention may be implemented in various forms and are not limited to the embodiments described in this specification.

[0026] Embodiments according to the concept of the present invention may have various modifications and take various forms, and thus, embodiments are illustrated in the drawings and described in detail in this specification. However, this is not intended to limit embodiments according to the concept of the present invention to specific disclosed forms, but rather includes modifications, equivalents, or alternatives that fall within the spirit and technical scope of the present invention.

[0027] While terms such as "first" or "second" may be used to describe various components, these components should not be limited by these terms. These terms are intended solely to distinguish one component from another. For example, a first component may be referred to as a "second component," and similarly, a second component may also be referred to as a "first component," without departing from the scope of the invention.

[0028] When a component is referred to as being "connected" or "connected" to another component, it should be understood that it may be directly connected or connected to that other component, but that there may be other components in between. Conversely, when a component is referred to as being "directly connected" or "directly connected" to another component, it should be understood that there are no other components in between. Expressions that describe relationships between components, such as "between," "immediately between," or "directly adjacent to," should be interpreted similarly.

[0029] The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the present invention. The singular expressions include plural expressions unless the context clearly indicates otherwise. In this specification, it should be understood that the terms "comprises" or "has" are intended to specify the presence of a described feature, number, step, operation, component, part, or combination thereof, but do not preclude the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0030] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Terms defined in commonly used dictionaries should be interpreted as having a meaning consistent with their meaning in the context of the relevant technology, and will not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0031]

[0032] Hereinafter, embodiments will be described in detail with reference to the attached drawings. However, the scope of the patent application is not limited or restricted by these embodiments. The same reference numerals in each drawing represent the same components.

[0033] FIG. 1 is a diagram illustrating a schematic diagram of a bridge transistor according to one embodiment.

[0034] A bridge transistor according to one embodiment may include a base layer (112) that is stacked and separated from each other by a channel region on a substrate (111), an electrode layer that is stacked on each of the base layers (112) and includes a source electrode (113) and a drain electrode (114), and a bridge layer (121) that is stacked on the channel region, the bridge layer including a material that forms at least one junction among a homojunction, a heterojunction, or a Schottky junction with the base layers (112) that are stacked and separated from each other.

[0035] Drawing symbol 110 represents a bridge transistor before the bridge layer (121) is formed, and drawing symbol 120 represents a bridge transistor after the bridge layer (121) is formed.

[0036] According to one embodiment, the materials of the base layer (111) and the bridge layer (121) can be determined to induce early saturation characteristics of the drain current.

[0037] For example, the bridge layer (121) may include at least one material selected from the group consisting of p-type organic semiconductors such as C8-BTBT (C8-Benzothiophene), DNTT (Dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene), Au, or Ni.

[0038] A bridge transistor can be implemented by combining the base layer (111) with a p-type organic semiconductor, C8-BTBT, and the bridge layer (121) with Au.

[0039] Additionally, a bridge transistor can be implemented by combining a base layer (111) containing DNTT, which is a p-type organic semiconductor, and a bridge layer (121) containing Ni.

[0040] Additionally, a bridge transistor can be implemented by combining the base layer (111) with a p-type organic semiconductor, C8-BTBT, and the bridge layer (121) with a DNTT.

[0041] As shown in Fig. 1, after fabricating a device having two bases (112) separated from each other, it can first be confirmed through measurement that they are electrically disconnected. Afterwards, when a bridge layer (121) is deposited, the fabrication of the bridge transistor is completed. Measurement is performed by contacting the measuring instrument's tip to the source, drain, and gate electrodes, similar to conventional transistor measurements. Finally, how the electrical characteristics change depending on the material adopted for the bridge layer is specifically analyzed through Figs. 4a to 4d.

[0042] FIG. 2 is a drawing illustrating a manufacturing method of a bridge transistor according to one embodiment.

[0043] In a manufacturing method of a bridge transistor according to one embodiment, a base layer, which is a channel region separated from each other, is deposited on a substrate, a source electrode and a drain electrode are deposited to be laminated on each of the deposited base layers, and a bridge layer connecting the separated base layers is deposited, and a material that forms at least one junction with the base layer among a homojunction, a heterojunction, or a Schottky junction can be deposited.

[0044] Additionally, the bridge layer may include at least one material selected from the group consisting of p-type organic semiconductors C8-BTBT, DNTT, Au, or Ni.

[0045] As a more specific example, in order to manufacture the device, a p-si substrate having a 300 nm thick SiO2 is prepared (201), and cleaning is performed sequentially with IPA and Acetone, followed by drying with N2 gas. Afterwards, a drying process is performed at 120 degrees Celsius on a thermal stirrer (202). Then, an insulating film, CYTOP, is spin-coated thereon, and heat treatment is performed at 120 degrees Celsius for 30 minutes and at 150 degrees Celsius for 30 minutes (203). After the formation of the insulating film, a base semiconductor to be applied to the channel layer is deposited through a thermal evaporator (204). After that, after aligning the base semiconductor to the position, a metal to be used as the source and drain electrodes can be deposited (205).

[0046] After that, the device fabrication is completed by a process (206) of depositing a bridge layer in the middle of the channel layers that are intentionally separated from each other.

[0047] Both organic and inorganic semiconductors can be applied to the region corresponding to the base semiconductor layer. Furthermore, the bridge layer can be made of a semiconductor or metal capable of inducing a sufficient depletion layer in the base semiconductor through contact with the base layer.

[0048] Before the deposition of the base layer, the device has the source-drain electrodes deposited, and the semiconductors in the middle of the channel layer are physically separated, so the channel is also formed separately, preventing charge movement.

[0049] Afterwards, we deposited the bridge layer to change the internal resistance in the channel layer to confirm the charge transfer effect. We observed that the current increased as the gate voltage changed. As the drain voltage increased, we observed that the current value stopped increasing and saturated above a certain voltage.

[0050] Figures 3a to 3d illustrate the transfer curves of a typical p-type transistor.

[0051] Figure 3a is a graph (310) showing the electrical characteristics of a C8-BTBT channel, i.e., a device without a bridge layer, indicating that it cannot function as a transistor.

[0052] FIGS. 3b to 3d can perform the function of a transistor through a bridge layer, and FIG. 3b is a graph (320) showing the characteristics of a homojunction through C8-BTBT, 3c is a graph (330) showing the characteristics of a mobile junction using DNTT, and 3d is a graph (340) showing the characteristics of forming a Schottky junction using Au.

[0053] The graph for each junction shows the electrical characteristics according to the type of junction between the channel and the bridge layer.

[0054] The threshold voltage (VTh) values ​​of the bridge transistors using C8-BTBT, DNTT, and Au as bridges are -12.1 V, -8.55 V, and -18.2 V, respectively.

[0055] Extraction of VTh for each bridge transistor can be done by performing a linear fit to the plot of the square root of ID as a function of gate voltage (VG) where VD is:

[0056] Figures 4a to 4d are diagrams showing the transfer characteristics and output characteristics of a bridge transistor.

[0057] In particular, FIGS. 4a and 4c are graphs (410) showing the transfer characteristics and output characteristics of a bridge transistor in which C8-BTBT, a p-type organic semiconductor, is applied as a base region and Au is applied as a bridge layer.

[0058] In addition, Figures 4b and 4d show the transfer characteristics and output characteristics of a bridge transistor in which DNTT, a p-type organic semiconductor, is applied as a base region and Ni as a bridge layer.

[0059] The fabrication of the bridge transistor is completed by depositing the bridge layer (121). Measurements are performed, similar to conventional transistor measurements, by contacting the measuring instrument's tip with the source, drain, and gate electrodes. Finally, how the electrical characteristics change depending on the material selected for the bridge layer is specifically analyzed through Figures 4a to 4d.

[0060] As a result, Figures 4a to 4d show the transfer characteristics and output characteristics of a bridge transistor using C8-BTBT, a p-type organic semiconductor, as a base region and Au as a bridge layer, and a bridge transistor using DNTT, a p-type organic semiconductor, as a base region and Ni as a bridge layer. In the case of the first bridge transistor, it can be confirmed that the current increases linearly as the drain voltage increases in the output characteristics, and then saturation of the current occurs abruptly at a certain drain voltage. This phenomenon is prominent in the second bridge transistor, where the position of the drain voltage where the current saturates hardly changes even when the gate voltage increases, and it can be seen that it is formed close to 0 V. Through this, it was shown that early saturation characteristics of the drain current can be induced by appropriately selecting the materials of the base semiconductor and the bridge layer.

[0061] Figures 5a to 5d are drawings (510 to 540) showing the output curves of each bridge transistor when the separated C8-BTBT channels are connected to the C8-BTBT, DNTT, and AU bridges, respectively.

[0062] The output curves of the C8-BTBT channel-based bridge transistor are disclosed in FIGS. 5a to 5c.

[0063] The output curves for all cases using C8-BTBT, DNTT, and AU as bridges exhibit saturation behavior in the drain current (ID). To extract the saturation voltage (VSAT), a linear fit can first be performed in the flat region of the drain current corresponding to the saturation region of each output curve.

[0064] Afterwards, the point just before leaving the linear fitting line can be defined as the saturation voltage.

[0065] When C8-BTBT and DNTT were used as bridges, the saturation voltages were almost identical. Furthermore, when Au was used as a bridge, the transistor reached saturation faster than when C8-BTBT and DNTT were used as bridges.

[0066] This can be accurately determined by plotting the VSAT of each bridge transistor as a function of the gate voltage (VG).

[0067] Looking at Fig. 5d, the VSAT of each bridge transistor is compared (540) and the VSAT when C8-BTBT and DNTT are used as bridges are similar in VG. Accordingly, the slope of the VSAT-VG plot, which indicates the degree of change in VSAT with respect to VG, is very similar at 0.89 VV-1 for the C8-BTBT bridge and 0.9 VV-1 when DNTT is used as a bridge. On the other hand, when Au is used as a bridge, VSAT was extracted at a lower VG than all other bridges.

[0068] Figures 6a and 6b are drawings (610, 620) showing the contact resistance or channel resistance of each transistor for VD extracted through the G-function method based on the measured output curve.

[0069] As shown in Figures 6a and 6b, the difference in VSAT between the Au bridge and the C8-BTBT, DNTT bridge increases as VG increases, which means that the change in VSAT with respect to VG is smaller in the Au bridge than in the other two bridges.

[0070] To investigate why the ID saturates relatively early when the Au bridge is introduced, the contact and channel resistances can be extracted from the measured output curves of each bridge transistor and compared.

[0071] To extract contact and channel resistances, a G-function method based on previously reported single device measurements can be used.

[0072] When the bridge is C8-BTBT, DNTT, and Au, the maximum contact resistances are 0.933, 0.588, and 1.79 M, respectively. In cm, when Au is the bridge, it is about twice as high as the other two bridges.

[0073] On the other hand, in terms of channel resistance, the DNTT bridge is relatively the highest, followed by C8-BTBT and Au, but unlike the contact resistance, the difference between the three bridge transistors is negligible.

[0074] Next, finite element numerical simulations (ATLAS version 5.34.0.R, Silvaco) based on the drift-diffusion framework are performed to calculate the hole distribution within the active channel of all three types of bridge transistors. In the simulations, the work function of Au is assumed to be 4.7 eV, and the ionization energy can be assumed to be 5.0 for DNTT and 5.3 eV for C8-BTBT. In addition, the hole mobility can be assumed to be 0.5 for DNTT and 1.0 cm2·V1·s1 for C8-BTBT.

[0075] Figures 7a to 7f are diagrams showing simulated hole distributions inside the active channel of a transistor based on C8-BTBT, DNTT, and AU bridges.

[0076] For FIGS. 7a and 7b, the entire channel can operate as an effective single medium because there is no energy mismatch between the base and the bridge.

[0077] In Fig. 7a, it can be seen that channel pinch-off uniquely occurs near the drain electrode, and the C8-BTBT bridge transistor exhibits a typical vertical distribution (710) of accumulated charge carriers.

[0078] However, as seen in the drawing reference numerals 730 and 740 of FIGS. 7c and 7d, for the DNTT and C8-BTBT bridges, the accumulation and depletion of holes in the vertical overlapping region occur in the DNTT and C8-BTBT, respectively, according to the HOMO offset (0.8 eV).

[0079] Figure 7c shows that the vertical hole distribution on the insulator surface becomes less monotonous than in Figure 7a due to depletion caused by DNTT in C8-BTBT (730). This depletion effect induces premature saturation. Analysis of the electrical characteristics of each bridge reveals that premature saturation is observed in the Au bridge due to additional contact resistance at the junction with the channel.

[0080] Two-dimensional simulations revealed that channel depletion occurred at the junction with the Au bridge, resulting in premature saturation. Since the bridge transistor according to the present invention controls transistor characteristics through the junction between materials in the middle of the channel, these characteristics can be utilized to develop various TFT characteristics.

[0081] Figure 7d shows that applying a higher gate electric field can make the depletion effect at the insulator surface almost invisible (740).

[0082] Simulation results for a transistor using an Au bridge are shown in Figures 7e and 7f (750, 760). The depletion effect in this case is much stronger than that of a transistor using a DNTT bridge due to the higher hole injection barrier (0.6 eV) established between the Au and C8-BTBT.

[0083] As shown in Fig. 7e, Fig. 750, the organic channel is confirmed to be completely depleted at the source-side C8-BTBT / Au junction. Source-side depletion can generally be considered the cause of initial saturation in SGTs. Therefore, the strong depletion region observed in Fig. 7e can explain the initial saturation behavior of the Au bridge transistor.

[0084] Finally, the proposed bridge transistor presents a novel structure that induces an additional junction in the central part of the channel.

[0085] In addition, in terms of electrical characteristics, unlike general transistors, along with structural novelty, it can induce saturation of drain current at a drain voltage close to 0 V, and has the characteristic that the increase in saturation voltage with increasing gate voltage is very small.

[0086] In addition, the bridge transistor structure with structural novelty and electrical characteristics can be considered as another parameter for controlling the characteristics of the transistor and designing the device.

[0087]

[0088] Although the embodiments described above have been described with limited drawings, those skilled in the art will recognize that various modifications and variations can be made based on the above description. For example, appropriate results can still be achieved even if the described techniques are performed in a different order than described, and / or components of the described systems, structures, devices, circuits, etc. are combined or combined in a different manner than described, or are replaced or substituted with other components or equivalents.

[0089] Therefore, other implementations, other embodiments, and equivalents to the claims also fall within the scope of the claims described below.

Claims

1. A base layer in which channel regions are laminated and separated from each other on a substrate; An electrode layer laminated on each of the above base layers and including a source electrode and a drain electrode; and A bridge layer laminated in the channel region, comprising a material that forms at least one junction among a homojunction, a heterojunction, or a Schottky junction with the base layer laminated separately from each other. A bridge transistor characterized by including:

2. In paragraph 1, A bridge transistor characterized in that the materials of the base layer and the bridge layer are determined so as to induce early saturation characteristics of the drain current.

3. In paragraph 1, A bridge transistor characterized in that the bridge layer includes at least one material selected from the group consisting of p-type organic semiconductors C8-BTBT (C8-Benzothiophene), DNTT (Dinaphtho[2,3-b:2',3'-f]thieno[3,2-b]thiophene), Au, and Ni.

4. In paragraph 1, A bridge transistor characterized in that the base layer includes C8-BTBT, which is a p-type organic semiconductor, and the bridge layer includes Au.

5. In paragraph 1, A bridge transistor characterized in that the base layer includes DNTT, which is a p-type organic semiconductor, and the bridge layer includes Ni.

6. In paragraph 1, A bridge transistor characterized in that the base layer includes C8-BTBT, which is a p-type organic semiconductor, and the bridge layer includes DNTT.

7. A step of depositing a base layer separated from each other by a channel region on a substrate; A step of depositing a source electrode and a drain electrode by laminating them on each of the above-deposited base layers; A step of depositing a bridge layer in the channel region, and depositing a material that forms at least one junction among a homojunction, a heterojunction, or a Schottky junction with the base layer. A method for manufacturing a bridge transistor, characterized in that it includes:

8. In paragraph 7, A method for manufacturing a bridge transistor, characterized in that the bridge layer includes at least one material selected from the group consisting of C8-BTBT, DNTT, Au, and Ni, which are p-type organic semiconductors.

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