KR20090129270A - Organic pyroelectric sensors integrated in thin-film transistors and the method for producing the same - Google Patents

Abstract

PURPOSE: An organic pyroelectric sensors integrated in thin-film transistors and a method for producing the same ARE provided to secure excellent linearity and reliability by adopting P(VDF-TrFE) within OTFT to as a functionality gate-dielectric layer. CONSTITUTION: In a device, an Ni gate electrode(2) is evaporated on a polyimide film(1) through electroplating in which is not contaminated. A gate dielectric is composed of P(VDF-TrFE) of 65mol% VDF. The Ni gate electrode is spin-coated with a mixture of 10wt% P(VDF-TrFE) and dimethylformamide solvent by 500nm. A DMF solvent is removed by performing a drying process under a temperature of 60°C. The gate dielectric is annealed on a hot plate until temperature is reached to 200°C. A pentacene layer(4) is evaporated by a thermal evaporator. Au source / drain electrodes(5,6) are evaporated on the pentacene layer.

Description

ORGANIC PYROELECTRIC SENSORS INTEGRATED IN THIN-FILM TRANSISTORS AND THE METHOD FOR PRODUCING THE SAME

The present invention relates to a sensor utilized as a gate dielectric layer directly on an OTFT structure so that a pyroelectric functional material can be applied to the sensor, and a manufacturing method thereof.

Since its application to electronic devices first appeared in 1987, research on organic thin film transistors (OTFTs) has been actively conducted. This is because there are advantages such as low cost, high performance, and high compatibility applicable to flexible electronic products compared to the conventional silicon technology. Recently, as an attempt to use the advantages of organic electronic devices to apply to various electronic components such as memory, RFID, sensors, etc., new functions of OTFTs and their integrated circuits are being considered.

In the case of functional organic devices, organic smart materials having ferromagnetic, piezoelectric and pyroelectric properties can be integrated directly into the OFTF device structure. Good materials applicable are polyvinylidene fluoride (PVDF) and copolymers of trifluorethylene with trifluoroethylene (P (VDF-TrFE)).

The piezoelectric and pyroelectric properties of PVDF and P (VDF-TrFE) have already been studied to a considerable extent and have been applied to various fields of research. However, this characteristic is limited to the extent to which OTFTs are applied to external sensing modules. In application in this field, there are generally disadvantages such as complicated manufacturing method and nonlinear response.

SUMMARY OF THE INVENTION An object of the present invention is to provide a sensor and a method of fabricating the same, which are utilized as a gate dielectric layer directly on an OTFT structure in order to solve the above problems and to apply a pyroelectric material to a sensor.

SUMMARY OF THE INVENTION In order to solve the above object, the present invention provides an organic pyroelectric sensor integrated in a thin film transistor, characterized in that the superelectric gate dielectric material is integrated into an organic thin film transistor structure as a gate dielectric layer.

In this case, the gate dielectric layer may include a pyroelectric gate dielectric material, a pyroelectric polymer thin film, a pyroelectric nanoparticle-PVDF based polymer composite material, a pyroelectric nanoparticle-P (VDF-TrFE) copolymer composite material, and an inorganic superplastic thin film gate. It is selected from the group consisting of a dielectric.

In addition, the pyroelectric polymer thin film is PVDF, or P (VDF-CTFE), P (VDF-CFE), P (VDF-HFP), P (VDF-CDFE), P (VDF-TrFE-CTFE), P (VDF -TrFE-CFE), P (VDF-TrFE-HFP), P (VDF-TrFE-CDFE), P (VDF-TFE-CTFE), P (VDF-TFE-CFE), P (VDF-TFE-HFP) And a PVDF based copolymer comprising P (VDF-TFE-CDFE).

And the second electric nanoparticles are preferably selected from the group consisting of _{BaTiO 3, PbTiO 3, SrTiO 3} , (Ba, Sr) TiO 3 and (Pb, Zr) TiO _3.

The pyroelectric polymer may be PVDF or P (VDF-CTFE), P (VDF-CFE), P (VDF-HFP), P (VDF-CDFE), P (VDF-TrFE-CTFE), P (VDF- TrFE-CFE), P (VDF-TrFE-HFP), P (VDF-TrFE-CDFE), P (VDF-TFE-CTFE), P (VDF-TFE-CFE), P (VDF-TFE-HFP), And P (VDF-TFE-CDFE).

The second electric inorganic gate dielectric is preferably selected from the group consisting of _{BaTiO 3, PbTiO 3, SrTiO 3} , (Ba, Sr) TiO 3, and (PbZr) TiO 3.

In another aspect, the present invention provides a method for manufacturing an organic pyroelectric sensor integrated in a thin film transistor consisting of the following steps.

Depositing a Ni gate electrode on the film by electroplating on the substrate;

Applying a P (VDF-TrFE) layer on the Ni gate electrode to form a dielectric layer;

Annealing and dissolving the dielectric layer to recrystallize to improve crystallinity;

Depositing a semiconductor layer, a source and a drain electrode layer over the dielectric layer.

At this time, the method of coating P (VDF-TrFE) is not particularly limited, but is preferably applied by spin coating. In a preferred embodiment, P (VDF-TrFE) is applied by dissolving at a concentration of 10wt% in a dimethylformamide solvent.

The material of the substrate need not be limited as well, but polyimide may be used as a preferred example.

Moreover, it is preferable that the material of a semiconductor layer is pentacene.

Meanwhile, in the method of manufacturing the organic pyroelectric sensor of the present invention, it is preferable to further include the step of grounding the source / drain electrodes and performing polling by applying a negative bias to the gate electrodes. At this time, the bias is preferably made at a voltage of -40V. In addition, it is preferable that polling is performed continuously except at the time of a measurement.

The present invention is meaningful in that it is applied to temperature sensing applications for the first time by using a highly crystalline P (VDF-TrFE) material having a very large residual polarization as a superelectric gate insulator layer in an OTFT structure. According to such a structure, a manufacturing process becomes simple compared with an external sensing module.

On the other hand, a polling strategy based on a step-wise poling process has been introduced to improve the effect of the pyroelectric on transistor performance. In addition, a new polling and measuring method is introduced to obtain the rapid response and linear characteristics of the thermal sensor. And the present inventors investigated the thermal behavior of the functional OTFT (functional OTFT), and as a result confirmed that the linear response under the phase transition temperature of P (VDF-TrFE). On the other hand, a polling operation mode (poling operation mode) was introduced to obtain a stable and reliable performance in the application to the temperature sensor. In other words, the polling operation mode was applied to avoid the reduction of polarization due to the thermal vibration observed at high temperature, and the positive pyroelectric contribution of the high crystalline β phase by the thermal expansion mechanism was used.

According to the present invention, by introducing P (VDF-TrFE) into the functional gate dielectric layer in the OTFT, it is possible to provide an organic pyroelectric sensor having a simple structure, fast response, and excellent linearity and reliability. In particular, since the linear response of the device can be secured in a specific temperature range, it can exhibit excellent performance when used as a pyroelectric thermal sensor. As a result, it can be effectively applied to smart organic dielectric materials in various fields.

Hereinafter, the present invention will be described in detail through preferred embodiments.

1 is a process of manufacturing an organic pyroelectric sensor integrated in a thin film transistor according to the present embodiment, and FIG. 2 schematically shows the device thus manufactured.

First, the Ni gate electrode 2 was deposited by electroplating on the uncontaminated polyimide film 1. The material of the gate dielectric is P (VDF-TrFE) of 65 mol% VDF purchased from Piezotech S.A. A solution in which 10 wt% P (VDF-TrFE) was dissolved in a dimethylformamide (DMF) solvent was spin coated on a Ni gate electrode to form a layer 3 having a thickness of 500 nm. In general, the thickness of the coating is preferably 400 nm or more.

The capacitance measured for the deposited 500 nm thickness P (VDF-TrFE) was 16.23 nF / cm ² and the dielectric constant was 9.17. The measurement conditions were 0.1 V DC voltage conditions at 1 kHz, with the DC bias changing between -20 and 20 V. This value was slightly smaller than the previously reported dielectric constant of 10-12. This result may be due to the high crystallinity of the material. The capacitance is determined by the filed-induced polarization of the non-polarized material, which disappears when the applied electric field is removed. For P (VDF-TrFE), the inductive polarization is due to the polar molecules in the amorphous phase and must be distinguished from the residual polarization P _r due to the dipole moment between the polymer chains in the β phase crystals. In the case of the present invention, recrystallization of the P (VDF-TrFE) layer in the molten metal yields most or amorphous portions of the highly crystalline β phase. This explains why a small amount of capacitance is obtained.

On the other hand, at the same thickness, the capacitance of polled P (VDF-TrFE) is 3.98 nF / cm ² , which is 1/4 of the deposited film. This may be due to the high internal electric field due to residual polarization. Since this internal electric field is a relatively high value equivalent to a 132 V bias, the inductive polarization is prevented from being set to a small applied voltage (-20 to 20 V). Thus, the capacitance is reduced. The surface charge density was calculated to be 5.25 mC / m ² .

This was followed by drying at 60 ° C. to remove the DMF solvent. Next, the gate dielectric layer was annealed completely on a hotplate at temperature conditions up to 200 ° C. The layer was maintained at 140 ° C. for 2 hours in a nitrogen atmosphere and then naturally dried to room temperature to improve phase crystallinity. This process leads to recrystallization. Next, the pentacene layer 4 was deposited by a thermal evaporator, followed by the deposition of Au source / drain electrodes 5 and 6.

FIG. 3 is a diagram schematically illustrating a polling process for the OTFT thus manufactured, and FIG. 4 is a diagram schematically illustrating a temperature measurement process in the OTFT of FIG. 1.

As shown in the figure, by biasing the gate electrode with a voltage of the V _G from 0 to -40V (9), a sequential polling step for a grounded source / drain electrodes (7, 8) were carried out. That is, the sequential polling method was performed by biasing the gate electrode to -40V at a room temperature device including the grounded source / drain electrodes. The polling electric field is applied up to 80 MV / cm. At this time, the pentacene layer functions as a conductive layer. The sample was heated to 80 ° C. while continuously polling at −40 V, maintained at that temperature for 2 hours, and finally cooled to room temperature to maximize polling effect. The P (VDF-trFE) layer was polled as the MIM structure and the dipoles were aligned along the polling direction.

Referring to FIG. 4, the output characteristics of the device on the hot chuck after polling were measured for various temperatures. The measurement conditions were negative drain bias 11 of -10, -20, -30, -40V at a gate bias of -40V. To prevent the thermal vibration effect, the device continued to poll except when measured. As a result, the thermal response of the sensor was linear, and the sensitivity was 4.38 V / ° C. as described later with respect to FIG. 5.

After polling at high temperature, the dipole of P (VDF-TrFE) changes state with increasing temperature. Because of the polarization of the P (VDF-TrFE) layer after polling, the output characteristic of the polled device has been increased to have an additional equivalent voltage Vo (10). At this time, two phenomena exist. One is thermal vibration, where the dipole vibrates in the polling direction to reduce polarization. The other is thermal expansion, where the dipole moment expands as the crystal in the P (VDF-TrFE) layer increases. This behavior increases the polarization of the gate dielectric layer. By maintaining the polling process except at the time of measurement, the dipoles were kept in the polling direction, thereby minimizing the effects of thermal vibration. The power consumption of the sensor is negligible because the polling current is the leakage current of the gate dielectric layer, which is about 1x10 ^-11 A.

5A and 5B are graphs showing temperature response and sensitivity of the organic pyroelectric sensor manufactured by one embodiment of the present invention.

As shown in FIG. 5A, the change in I _{D with} temperature depends on the measurement conditions, and therefore, device sensitivity may be defined as dV ₀ / dT. The change of V ₀ with respect to the temperature obtained by the I _D -V _D characteristic is shown in FIG. 5B, and the sensitivity (dV ₀ / dT) was calculated to be 4.38 V / ° C. FIG. Slightly exponential drain current behavior was observed above 60 ° C (not shown), which may be attributed to changes in field effect channel mobility at high temperatures. Repeated measurements in the range of 25 to 60 ° C. resulted in a maximum error of V ₀ of 29.81 V, which was about 6.8 ° C., and the maximum error of V ₀ was 95.24 V or 21.7 ° C. when the upper temperature limit was extended to 80 ° C.

Although the present invention has been described through the preferred embodiments, the spirit of the present invention is not limited to the specific embodiments. Therefore, it is to be understood that the scope of the invention is defined by the matter set forth in the appended claims.

1 is a flowchart illustrating a manufacturing process of an OTFT according to an embodiment of the present invention.

2 is a diagram schematically showing a structure of an OTFT according to an embodiment of the present invention.

FIG. 3 is a diagram schematically illustrating a polling process for the OTFT of FIG. 1.

4 is a diagram schematically illustrating a temperature measurement process in the OTFT of FIG. 1.

Figure 5 is a graph showing the temperature response and sensitivity of the organic pyroelectric sensor manufactured by one embodiment of the present invention.

Brief description of symbols for the main parts of the drawings

1: polyimide substrate 2: Ni electroplated gate electrode

3: P (VDF-TrFE) layer 4: pentacene layer

5: Au deposited source electrode 6: Au deposited drain electrode

7: Source electrode ground 8: Drain electrode ground

9: Negative Gate Bias 10: Equivalent Voltage V ₀ After Polling of P (VDF-TrFE) Layer

11: negative drain bias

Claims (17)

An organic superelectric sensor integrated in a thin film transistor, characterized in that the superelectric gate dielectric material is integrated into the organic thin film transistor structure as a gate dielectric layer. The method of claim 1, The gate dielectric layer may include a pyroelectric gate dielectric material, a pyroelectric polymer thin film, a pyroelectric nanoparticle-PVDF based polymer composite, a pyroelectric nanoparticle-P (VDF-TrFE) copolymer composite, and an inorganic superplastic thin film gate dielectric An organic pyroelectric sensor integrated in a thin film transistor, characterized in that selected from the group consisting of. The method of claim 2, The pyroelectric polymer thin film is PVDF, or P (VDF-CTFE), P (VDF-CFE), P (VDF-HFP), P (VDF-CDFE), P (VDF-TrFE-CTFE), P (VDF- TrFE-CFE), P (VDF-TrFE-HFP), P (VDF-TrFE-CDFE), P (VDF-TFE-CTFE), P (VDF-TFE-CFE), P (VDF-TFE-HFP) and An organic pyroelectric sensor integrated in a thin film transistor, characterized in that it is a PVDF based copolymer comprising P (VDF-TFE-CDFE). The method of claim 2, Wherein the second electrical nanoparticles _{BaTiO 3, PbTiO 3, SrTiO 3} , (Ba, Sr) TiO 3 and (Pb, Zr) TiO ₃ Organic second electrical sensor integrated in the thin film transistor characterized in that the member selected from the group consisting of . The method of claim 2, The pyroelectric polymer is PVDF, or P (VDF-CTFE), P (VDF-CFE), P (VDF-HFP), P (VDF-CDFE), P (VDF-TrFE-CTFE), P (VDF-TrFE -CFE), P (VDF-TrFE-HFP), P (VDF-TrFE-CDFE), P (VDF-TFE-CTFE), P (VDF-TFE-CFE), P (VDF-TFE-HFP), and An organic pyroelectric sensor integrated in a thin film transistor, which is a polymer selected from the group consisting of P (VDF-TFE-CDFE). The method of claim 2, The second electric inorganic gate dielectric is _{BaTiO 3, PbTiO 3, SrTiO 3} , (Ba, Sr) TiO 3, and (PbZr) an organic second electrical sensor integrated in the thin film transistor characterized in that the member selected from the group consisting of TiO ₃ . Depositing a Ni gate electrode on the film by electroplating on the substrate; Applying a P (VDF-TrFE) layer on the Ni gate electrode to form a dielectric layer; Annealing and dissolving the dielectric layer to recrystallize to improve crystallinity; Depositing a semiconductor layer, a source and a drain electrode layer over the dielectric layer. 8. A method according to claim 7, wherein said P (VDF-TrFE) is applied by spin coating. The method according to claim 8, wherein the P (VDF-TrFE) is dissolved and applied at a concentration of 10 wt% in a dimethylformamide solvent. The method according to claim 7, wherein the substrate is made of polyimide. The method according to claim 7, wherein the thickness of the P (VDF-TrFE) layer is 400 nm or more. The method of manufacturing an organic pyroelectric sensor integrated in a thin film transistor according to claim 7, wherein the semiconductor layer is made of pentacene. 8. The method of claim 7, further comprising the step of grounding the source / drain electrodes and applying a negative bias to the gate electrodes to perform polling. The method of manufacturing an organic pyroelectric sensor integrated in a thin film transistor according to claim 13, wherein a polling electric field of 80 MV / cm is applied. The method of manufacturing an organic pyroelectric sensor integrated in a thin film transistor according to claim 13, wherein the polling is performed continuously. The thin film transistor of claim 13, further comprising maximizing a polling effect by heating to room temperature at a constant temperature, maintaining the temperature for a predetermined time, and finally cooling to room temperature to perform polling. The manufacturing method of the organic pyroelectric sensor integrated in the inside. 17. The method of manufacturing an organic pyroelectric sensor integrated in a thin film transistor according to claim 16, wherein the heating is performed up to 80 DEG C and maintained for 2 hours in the state.

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