Flexible threshold voltage tunable negative capacitance transistor and method of fabrication, compact logic circuit

Abstract

The application belongs to the technical field of organic semiconductor electronic devices, and discloses a flexible threshold value adjustable negative capacitance transistor and a preparation method, and a small logic circuit. The flexible threshold value adjustable negative capacitance transistor comprises a flexible substrate, an organic semiconductor layer, an organic dielectric layer, a source-drain electrode and two gate electrodes. The preparation method is as follows: a bottom gate electrode is prepared on the surface of the flexible substrate and an organic ferroelectric film is spin-coated; an organic polymer film is spin-coated on the surface of the organic dielectric layer as a semiconductor channel layer; a source / drain metal electrode is prepared; finally, an organic ferroelectric film is spin-coated and a top gate electrode is prepared. The application utilizes the negative capacitance principle of the organic ferroelectric transistor to reduce the working voltage and power consumption, and the double-gate structure is made to make the threshold voltage of the transistor adjustable, which has a great effect in the flexible logic circuit based on the unipolar device.

Description

Technical Field

[0001] This invention belongs to the field of organic semiconductor electronic device technology, specifically relating to a transistor and its small logic circuit, particularly a flexible threshold adjustable negative capacitance transistor and its preparation method, and a small logic circuit. Background Technology

[0002] Organic semiconductors have garnered significant attention in recent years due to their wide range of material choices, low cost, and compatibility with flexible devices. Organic transistors, as crucial components, play a vital role in sensors, organic digital circuits, and wearable electronics. However, compared to today's mainstream silicon-based transistors and novel transistors using two-dimensional materials like carbon nanotubes as the semiconductor layer, organic transistors still face numerous challenges.

[0003] For organic transistors, the operating voltage of conventional organic transistors is relatively high, leading to increased dynamic power consumption. Furthermore, because small logic circuits based on unipolar devices require different threshold voltages for transistors, the threshold voltage of conventional organic transistors is not adjustable. Summary of the Invention

[0004] To address the aforementioned issues, this invention provides a flexible threshold-adjustable negative capacitance transistor, its fabrication method, and a small logic circuit. This flexible threshold-adjustable negative capacitance transistor incorporates a dual-gate structure, precisely controlling the shift of the threshold voltage of the organic negative capacitance transistor with an extremely small top-gate voltage, and fabricating a small flexible circuit.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solution:

[0006] This invention relates to a flexible threshold-adjustable negative capacitance transistor, comprising a flexible substrate, a bottom gate metal electrode disposed on the surface of the flexible substrate, an organic dielectric layer and an organic semiconductor channel layer disposed on the surface of the bottom gate metal electrode, a source electrode and a drain electrode fabricated on the surface of the organic semiconductor channel layer, an organic ferroelectric layer disposed on the surface of the source electrode and the drain electrode, and a top gate electrode disposed on the surface of the organic ferroelectric layer. The bottom gate metal electrode controls the switching of the transistor, and the top gate electrode controls the movement of the transistor threshold voltage.

[0007] For a P-type transistor, when a positive pulse is applied to the top gate electrode, the transistor's transfer characteristic curve will shift in the negative direction, and the threshold voltage V... TH Consequently, it shifts in the negative direction. When a negative pulse is applied to the top gate electrode, the transistor's transfer characteristic curve will shift in the positive direction, and the threshold voltage V... TH It also moves in the positive direction.

[0008] For an n-type transistor, when a positive pulse is applied to the top gate electrode, the transistor's transfer characteristic curve will shift in the negative direction, and the threshold voltage V... TH It also shifts in the negative direction. When a negative pulse is applied to the top gate electrode, the transistor's transfer characteristic curve will shift in the positive direction, and the threshold voltage V... TH It also moves in the positive direction.

[0009] A further improvement of the present invention is that the organic dielectric layer is an organic ferroelectric material layer.

[0010] A further improvement of the present invention is that the organic dielectric layer is PVDF or PVDF-TrFE.

[0011] A further improvement of the present invention is that the organic semiconductor channel layer is an organic polymer thin film layer.

[0012] A further improvement of the present invention is that the organic semiconductor channel layer is poly(dithiophene-pyrrolopyrroledione) (DPPT-TT).

[0013] A further improvement of the present invention is that the flexible substrate is PVA or PET.

[0014] A further improvement of the present invention is that the source electrode and the drain electrode are metals such as gold, platinum, silver, and titanium / gold.

[0015] A further improvement of the present invention is that the top gate electrode is made of gold, aluminum or platinum, preferably platinum.

[0016] This invention also provides a method for fabricating a flexible threshold-adjustable negative capacitance transistor, the method comprising the following steps:

[0017] Step 1: Fabricate the bottom gate metal electrode on a flexible substrate using thermal evaporation or van der Waals processes;

[0018] Step 2: Spin-coating an organic dielectric layer and an organic semiconductor channel layer sequentially onto the surface of the bottom gate metal electrode using a spin-coating method;

[0019] Step 3: Fabricate source and drain electrodes on the thin film surface of the organic semiconductor channel layer using vapor deposition or van der Waals processes;

[0020] Step 4: Apply an organic ferroelectric layer to the surfaces of the source and drain electrodes using a spin coating method.

[0021] Step 5: Fabricate the top gate electrode on the thin film surface of the organic ferroelectric layer using thermal evaporation or van der Waals processes.

[0022] The present invention also provides a small logic circuit comprising a load-type flexible threshold-adjustable negative capacitor transistor and a drive-type flexible threshold-adjustable negative capacitor transistor.

[0023] The beneficial effects of this invention are:

[0024] First, compared with traditional organic transistors, the organic ferroelectric flexible threshold adjustable negative capacitance transistor of the present invention reduces operating voltage and power consumption.

[0025] Secondly, the transistor provides a dual-gate structure, which can achieve precise control of the threshold voltage of the negative capacitance transistor using a very small top gate voltage. Only one pulse is needed for control, which greatly reduces the control voltage and is of great significance in logic circuits based on unipolar devices.

[0026] Furthermore, apart from the electrode material, all other components of the transistor in this invention are made of organic, flexible materials, making it wearable. This gives it excellent resistance to bending and stretching when fabricated on flexible substrates such as PET and PVA. Moreover, the fabrication process is significantly less expensive than that of traditional inorganic transistors, making it a promising candidate for low-cost, low-power wearable devices.

[0027] Furthermore, this invention can also be used for the detection of electrophysiological signals in the human brain. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the flexible threshold adjustable negative capacitance transistor structure of the present invention.

[0029] Figure 2 This is a hysteresis curve of the ferroelectric material of the present invention.

[0030] Figure 3 This is a schematic diagram of the threshold voltage regulation of the flexible threshold adjustable negative capacitance transistor of the present invention.

[0031] Figure 4 This invention relates to a unipolar device circuit using a threshold-adjustable negative capacitance crystal; wherein (a) is a dual P-type inverter, (b) is a NAND gate, and (c) is a NOR gate.

[0032] Figure 5 This is a structural diagram of an integrated pulse sensor that uses a threshold-adjustable negative capacitance transistor and an amplifier circuit. Detailed Implementation

[0033] The embodiments of the present invention will be disclosed below with reference to the drawings. For clarity, many practical details will be described in the following description. However, it should be understood that these practical details are not intended to limit the invention. That is, in some embodiments of the invention, these practical details are not essential.

[0034] like Figure 1As shown, this invention relates to a flexible threshold-adjustable negative capacitance transistor. The negative capacitance transistor includes a flexible substrate, a bottom gate metal electrode disposed on the surface of the flexible substrate, and an organic dielectric layer and an organic semiconductor channel layer disposed on the surface of the bottom gate metal electrode. The organic dielectric layer is any organic ferroelectric material, such as PVDF, PVDF-TrFE, etc. An organic ferroelectric solution is spin-coated onto the surface of the bottom gate electrode, and the electrode is placed on a heating stage for annealing to form a thin film. The organic semiconductor channel layer is any organic polymer material, such as poly(dithiophene-pyrrolopyrroledione) (DPPT-TT).

[0035] Source and drain electrodes are prepared on the surface of the organic semiconductor channel layer. The source and drain electrodes are metals such as gold, platinum, silver, and titanium / gold. Gold electrodes are preferred as source and drain electrodes. They are transferred to the surface of the semiconductor thin film using a van der Waals process.

[0036] An organic ferroelectric layer is formed on the surface of the source electrode and the drain electrode. The organic ferroelectric layer is an organic ferroelectric thin film.

[0037] A top gate electrode, preferably a platinum electrode, is disposed on the surface of the organic ferroelectric layer. The bottom gate metal electrode controls the switching of the transistor, and the top gate electrode controls the shift of the transistor's threshold voltage. For a P-type transistor, when a positive pulse is applied to the top gate electrode, the transistor's transfer characteristic curve will shift in the negative direction, and the threshold voltage V... TH Consequently, it shifts in the negative direction. When a negative pulse is applied to the top gate electrode, the transistor's transfer characteristic curve will shift in the positive direction, and the threshold voltage V... TH Consequently, the transfer characteristic curve of an n-type transistor shifts in the positive direction when a positive pulse is applied to the top gate electrode, and the threshold voltage V... TH It also shifts in the negative direction. When a negative pulse is applied to the top gate electrode, the transistor's transfer characteristic curve will shift in the positive direction, and the threshold voltage V... TH It also moves in the positive direction.

[0038] This flexible threshold-adjustable negative capacitance transistor is fabricated using the following method.

[0039] 1. Step 1: Use either PVA or PET as a flexible substrate and prepare source / drain electrodes on its surface using a thermal evaporation method under high temperature conditions, or use the van der Waals process to prepare source / drain electrodes on the surface of a rigid substrate and then transfer them to a flexible substrate.

[0040] 2. An organic dielectric layer and an organic semiconductor channel layer are spin-coated onto the substrate surface in one step using a spin coating method.

[0041] The specific preparation method is as follows: the growth solution is dropped onto the dielectric layer surface using a pipette, and the growth solution is evenly spread using a spin coating method at different speeds such as 1500 rpm and 2000 rpm. Then, it is pre-annealed at 80℃ for 5 min and annealed at 150℃ for 1 h. The thickness of the spin-coated film in this example is about 20 nm. After the growth solution is prepared, it should be placed on a heating stage and heated at 80℃ for at least 24 h to ensure that the solution is fully dissolved.

[0042] 3. Source and drain electrodes are fabricated on the thin film surface of the organic semiconductor channel layer using vapor deposition or van der Waals processes; van der Waals transfer reduces the introduction of interface states and improves transistor performance.

[0043] 4. Under these conditions, prepare an organic ferroelectric thin film using the same parameters as in step 2, and fabricate the top gate electrode using thermal evaporation or van der Waals processes. Utilizing the principle of the negative capacitance effect of ferroelectric materials, precise control of the threshold voltage can be achieved by applying only a very small gate voltage to the top gate electrode while maintaining the high-performance transfer characteristic curve of the transistor. For example, in an inverter composed of unipolar devices, the two P-type flexible transistors require different threshold voltages. Therefore, adjustable threshold voltage for organic transistors plays a significant role in inverter-based flexible logic circuits.

[0044] Figure 1 This is a schematic diagram of a flexible threshold-adjustable negative capacitance transistor. Compared to traditional organic negative capacitance transistors, this invention adds a gate organic ferroelectric layer and a top gate metal electrode. The device's operating principle will be explained later. Figure 2 and Figure 3 The explanation is provided below.

[0045] Figure 2 This is a hysteresis curve diagram for ferroelectric materials. Based on the characteristics of ferroelectric materials, adjustments can be made according to different requirements. When a steep subthreshold swing is needed, similar to the lower gate ferroelectric layer, the PV curve needs to be compressed. This means that the remanent polarization (Pr) should be small while the coercive field (Ec) should be large to meet the requirements of the logic circuit. The upper gate ferroelectric layer corresponds to its lower layer; the remanent polarization (Pr) should be large while the coercive field (Ec) should be small. This way, only a small pulse needs to be applied to the top gate electrode to achieve a shift in the transistor threshold voltage. The following section combines... Figure 3 The explanation will use the transfer characteristic curve of a P-type organic transistor as an example. When a positive pulse is applied to the top gate, the threshold voltage of the transistor will shift to the right, and vice versa.

[0046] Flexible threshold-adjustable negative capacitance transistors are of great significance in logic circuits based on unipolar devices due to their adjustable threshold voltage. The following section will use... Figure 4(a) uses a basic logic gate inverter composed of dual P-type flexible threshold adjustable negative capacitor transistors as an example. To achieve a transition from 0 to 1 or from 1 to 0, the threshold voltages of two P-type transistors with identical process parameters must be maintained at different, defined values. This fully demonstrates the advantage of the flexible threshold adjustable negative capacitor transistor. For example... Figure 4 (b) and 4(c) with Figure 3 The principle is the same; they are NAND and NOR gates based on negative capacitance transistors with adjustable flexible thresholds.

[0047] exist Figure 1 In the schematic diagram of the flexible threshold adjustable negative capacitance transistor, except for the source drain and dual gate electrodes which are metal, the materials of the remaining structural layers are all organic flexible materials. This gives it excellent bending and tensile strength when fabricated on flexible substrates such as PET and PVA. Moreover, the fabrication process is much cheaper than that of traditional inorganic transistors, making it a promising candidate for application in the field of wearable devices that require low cost and low power consumption. Figure 5 This demonstrates the application of a flexible threshold-adjustable negative capacitance transistor in the field of flexible devices. It is an integrated pulse sensor that combines a threshold-adjustable negative capacitance transistor with an amplifier circuit, which can be used to detect electrophysiological signals in the human brain.

[0048] This invention utilizes the negative capacitance principle of organic ferroelectric transistors to reduce operating voltage and power consumption. Based on this, a dual-gate structure is fabricated to make the transistor's threshold voltage adjustable, which plays a significant role in flexible logic circuits based on unipolar devices. This method has potential for development in the field of fabricating flexible electronic devices with high portability, wearability, portability, and lightweight characteristics.

[0049] The above description is merely an embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principle of the present invention should be included within the scope of the claims of the present invention.

Claims

1. A flexible threshold-adjustable negative capacitance transistor, the negative capacitance transistor comprising a flexible substrate, characterized in that: A bottom gate metal electrode is disposed on the surface of the flexible substrate. An organic dielectric layer and an organic semiconductor channel layer are disposed on the surface of the bottom gate metal electrode. A source electrode and a drain electrode are fabricated on the surface of the organic semiconductor channel layer. An organic ferroelectric layer is disposed on the surface of the source electrode and the drain electrode. A top gate electrode is disposed on the surface of the organic ferroelectric layer. The bottom gate metal electrode controls the switching of the transistor, and the top gate electrode controls the shift of the transistor's threshold voltage. For a P-type transistor, when a positive pulse is applied to the top gate electrode, the transistor's transfer characteristic curve will shift in the negative direction, and the threshold voltage V... TH Consequently, it shifts in the negative direction. When a negative pulse is applied to the top gate electrode, the transistor's transfer characteristic curve will shift in the positive direction, and the threshold voltage V... TH Consequently, the transfer characteristic curve of an n-type transistor shifts in the positive direction when a positive pulse is applied to the top gate electrode, and the threshold voltage V... TH It also shifts in the negative direction. When a negative pulse is applied to the top gate electrode, the transistor's transfer characteristic curve will shift in the positive direction, and the threshold voltage V... TH It also moves in the positive direction, and the flexible substrate is PVA or PET.

2. The flexible threshold adjustable negative capacitance transistor according to claim 1, characterized in that: The organic dielectric layer is an organic ferroelectric material layer.

3. The flexible threshold adjustable negative capacitance transistor according to claim 2, characterized in that: The organic media layer is PVDF or PVDF-TrFE.

4. The flexible threshold adjustable negative capacitance transistor according to claim 1, characterized in that: The organic semiconductor channel layer is an organic polymer thin film layer.

5. The flexible threshold adjustable negative capacitance transistor according to claim 3, characterized in that: The organic semiconductor channel layer is poly(dithiophene-pyrrolopyrroledione) (DPPT-TT).

6. The flexible threshold-adjustable negative capacitance transistor according to any one of claims 1-5, characterized in that: The method for fabricating this transistor includes the following steps: Step 1: Fabricate the bottom gate metal electrode on a flexible substrate using thermal evaporation or van der Waals processes; Step 2: Spin-coating an organic dielectric layer and an organic semiconductor channel layer sequentially onto the surface of the bottom gate metal electrode using a spin-coating method; Step 3: Fabricate source and drain electrodes on the thin film surface of the organic semiconductor channel layer using vapor deposition or van der Waals processes; Step 4: Apply an organic ferroelectric layer to the surfaces of the source and drain electrodes using a spin coating method. Step 5: Fabricate the top gate electrode on the thin film surface of the organic ferroelectric layer using thermal evaporation or van der Waals processes.

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