Flexible bimodal sensor

A flexible bimodal sensor includes a gate electrode; a flexible substrate; a source electrode disposed on the flexible substrate; a drain electrode disposed on the flexible substrate apart from the source electrode; a channel layer disposed on the source electrode and the drain electrode and a portion of the flexible substrate between the source electrode and the drain electrode; and a gate insulating layer comprising a plurality of protrusions, the gate insulating layer being disposed on the channel layer and arranged between the channel layer and the gate electrode. The drain electrode outputs a current signal simultaneously indicating a temperature value and a pressure value sensed by the flexible bimodal sensor.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority from Korean Patent Application No. 10-2015-0094939, filed on Jul. 2, 2015 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

BACKGROUND

Apparatuses and methods consistent with exemplary embodiments relate to flexible bimodal sensors having a three-dimensional (3D) microstructure.

2. Description of the Related Art

A physical sensor, for example, a pressure sensor generally has a two-dimensional (2D) thin-film type structure. A pressure sensor of the related art has a pressure sensing range of a few hundred Kilo-Pascal or greater and is used for detecting a relatively high pressure.

However, in order to apply a pressure sensor to smart electronic devices, for example, wearable electronics, a highly sensitive pressure sensor may be needed to measure biorhythm changes of a human body in real-time. To this end, there is a need to manufacture a sensor device having a three-dimensional (3D) structure that may induce a large mechanical and electrical change even at a small pressure unlike a 2D structure of the related art.

Also, since a pressure detecting material is very sensitive to temperature, temperature interference may not be easily avoided. In order to simultaneously detect both temperature and pressure, a temperature sensor and a pressure sensor are integrated on the same substrate, and thus, a volume of a wearable electronic is increased.

SUMMARY

Exemplary embodiments address at least the above problems and/or disadvantages and other disadvantages not described above. Also, the exemplary embodiments are not required to overcome the disadvantages described above, and may not overcome any of the problems described above.

One or more exemplary embodiments provide flexible bimodal sensors having a 3D microstructure.

According to an aspect of an exemplary embodiment, there is provided a flexible bimodal sensor including: a gate electrode; a flexible substrate; a source electrode disposed on the flexible substrate; a drain electrode disposed on the flexible substrate apart from the source electrode; a channel layer disposed on the source electrode and the drain electrode and a portion of the flexible substrate between the source electrode and the drain electrode; and a gate insulating layer comprising a plurality of protrusions, the gate insulating layer being disposed on the channel layer and arranged between the channel layer and the gate electrode. The drain electrode may output a current signal simultaneously indicating a temperature value and a pressure value sensed by the flexible bimodal sensor.

The plurality of protrusions of the gate insulating layer may be protruded in a direction away from the gate electrode, and an air gap may exist between two adjacent protrusions of the plurality of protrusions.

The flexible bimodal sensor may further include a processor configured to obtain a channel trans-conductance value and an equilibrium voltage in the gate insulating layer from the current signal, and determine the temperature value and the pressure value based on an equation indicating a relationship between the channel trans-conductance value, the equilibrium voltage, the temperature value, and the pressure value.

The channel layer may include one of silicon, an organic semiconductor, and a semiconductor oxide.

The flexible bimodal sensor may further include an encapsulating layer that covers the channel layer and is disposed between the channel layer and the gate insulating layer.

The encapsulating layer may include one of an organic material comprising tetratetracontane (TTC) or methylcycloheane (MCH), an inorganic oxide comprising Al2O3or HfO2, and a stack structure in which the organic material and the inorganic oxide are stacked.

The gate insulating layer may include a base having a predetermined thickness and the plurality of protrusions extends from the base towards the channel layer.

The plurality of protrusions may include a plurality of first protrusions formed on a first surface of the base and a plurality of second protrusions formed on a second surface facing the first surface of the base.

The gate insulating layer may include a first material selected from the group consisting of P(VDF_TrFE), P(VDF-TrFE-CFE), P(VDF-TrFE-CtFE), polydimethylsiloxane (PDMS), and polyurethane (PU).

The gate insulating layer may further include inorganic nano-particles distributed in the first material.

The plurality of protrusions of the gate insulating layer may have a pyramid shape or a truncated pyramid shape.

The flexible bimodal sensor may be a plurality of bimodal sensors, and the plurality of bimodal sensors may be arranged in a matrix shape on the flexible substrate.

According to an aspect of another exemplary embodiment, there is provided a flexible bimodal sensor including: a flexible substrate; a gate electrode disposed on the flexible substrate; a gate insulating layer covering the gate electrode on the flexible substrate; a channel layer disposed on the gate insulating layer; and a source electrode disposed on the channel layer; and a drain electrode disposed on the channel layer apart from the source electrode, wherein the gate insulating layer comprises a plurality of protrusions, and the drain electrode outputs a current signal simultaneously indicating a temperature value and a pressure value measured by the flexible bimodal sensor.

DETAILED DESCRIPTION

Hereinafter, it will be understood that when an element or layer is referred to as being “on” or “above” another element or layer, the element or layer may be directly on another element or layer or intervening elements or layers.

FIG. 1is a schematic cross-sectional view of a flexible bimodal sensor100that includes a microstructure according to an exemplary embodiment.

Referring toFIG. 1, the flexible bimodal sensor100may include a source electrode121and a drain electrode122that are formed on a flexible substrate110. The source electrode121and the drain electrode122are separated from each other on the flexible substrate110.

A channel layer130is formed on the flexible substrate110to cover an exposed surface of the flexible substrate110between the source electrode121and the drain electrode122. Edges of the channel layer130are respectively connected to the source electrode121and the drain electrode122. An encapsulating layer140may be further formed on the channel layer130.

A gate insulating layer150is disposed on the encapsulating layer140. The gate insulating layer150may include a plurality of protrusions154that protrude towards the channel layer130from one side of the gate insulating layer150. The plurality of protrusions154may be formed to contact the encapsulating layer140. A gate electrode160is formed on another side of the gate insulating layer150. Under the structure, the plurality of protrusions154may be protruded in a direction away from the gate electrode160.

The flexible substrate110may be formed of a flexible polymer, such as polyethylene terephthalate (PET), polyimide (PI), polystyrene (PS), polyethersulfone (PES), or polyethylene naphthalate (PEN) or an elastic polymer, such as polydimethylsiloxane (PDMS), polyurethane (PU), Ecoflex®, or Dragon Skin®.

The channel layer130and the gate insulating layer150may be formed of a multi-stimuli responsive material. The channel layer130may be formed of a piezo-thermoresistive organic semiconductor, and the gate insulating layer150may be formed of a piezopyroelectric material. Temperature and pressure may be measured from a drain current of the flexible bimodal sensor100that is changed according to stimulation, such as pressure and temperature of the gate insulating layer150and the channel layer130.

However, the current exemplary embodiment is not limited thereto. That is, the channel layer130may be formed of silicon or a semiconductor oxide, such as zinc oxide, or indium gallium zinc oxide (IGZO). The organic semiconductor may be formed of pentacene. Semiconductor characteristics of an organic semiconductor, such as pentacene may be reduced by being reacted with oxygen or being contaminated by other materials.

The encapsulating layer140prevents the organic semiconductor from being reacted with oxygen or being contaminated with other materials. The encapsulating layer140may be formed at least to completely cover the organic semiconductor. The encapsulating layer140may be formed of an organic material including tetratetracontane (TTC) or methylcycloheane (MCH) or an inorganic oxide that includes Al2O3or HfO2. However, the current exemplary embodiment is not limited thereto. For example, the encapsulating layer140may have a structure in which the organic material and the inorganic oxide are sequentially stacked on the channel layer130.

The gate insulating layer150includes a base152having a predetermined thickness and the plurality of protrusions154extending from the base152. The plurality of protrusions154are disposed at a regular interval with predetermined gaps to form a pattern. The gate insulating layer150may be formed of a piezopyroelectric material, for example, P(VDF_TrFE), P(VDF-TrFE-CFE), or P(VDF-TrFE-CtFE). However, the current exemplary embodiment is not limited thereto. For example, the gate insulating layer150may be formed of PDMS or polyurethane (PU).

The gate insulating layer150may include a material selected from the group consisting of P(VDF_TrFE), P(VDF-TrFE-CFE), P(VDF-TrFE-CtFE), PDMS, and PU (hereinafter, referred to as a “first material”) as a matrix and inorganic nano-particles distributed in the first material. The inorganic nano-particles may include gallium orthophosphate (GaPO4), langasite (La3Ga5SiO14), a quartz analogic crystal, barium titanate (BaTiO3), lead titanate (PbTiO3), lead zirconate titanate (Pb[ZrxTi1-x]3,0≤x≤1), potassium niobate (KNbO3), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), sodium tungstate (Na2WO3), zinc oxide (Zn2O3), Ba2NaNb5O5, Pb2KNb5O15, sodium potassium niobate ((K,Na)NbO3), bismuth ferrite (BiFeO3), sodium niobate NaNbO3, bismuth titanate Bi4Ti3O12, or sodium bismuth titanate Na0.5Bi0.5TiO3.

The plurality of protrusions154of the gate insulating layer150may have a horn shape or a truncated horn shape.

The flexible bimodal sensor100may further include a processor and a memory. The processor may calculate temperature and pressure based on a drain current measured from the drain electrode122by using equations (e.g., Equations 1 and 2 described below) stored in the memory.

InFIG. 1, it is depicted that the plurality of protrusions154of the gate insulating layer150is in contact with the encapsulating layer140. However, the current exemplary embodiment is not limited thereto. For example, the plurality of protrusions154may be in contact with the gate electrode160.

FIG. 2is a scanning electron microscope (SEM) image showing a plurality of protrusions of a gate insulating layer of a flexible bimodal sensor according to an exemplary embodiment. Referring toFIG. 2, the plurality of protrusions is regularly formed in a matrix type.FIG. 2shows that the plurality of protrusions has a pyramid shape.

The gate insulating layer150having the plurality of protrusions154is formed by spin coating P(VDF_TrFE) on a stamp mold having a concave shape opposite to the shape of the plurality of protrusions154, heating the stamp mold at a temperature of 140° C. to form a P(VDF_TrFE) crystal, and transferring the P(VDF_TrFE) crystal onto the channel layer130.

FIG. 3is a graph showing a measured pressure sensing sensitivity of a flexible bimodal sensor by using the P(VDF_TrFE) as the gate insulating layer150. In order to measure a low pressure range, a drain current was measured after a predetermined weight is applied onto the gate electrode160of the flexible bimodal sensor100.

Referring toFIG. 3, it is known that the drain current IDof the flexible bimodal sensor100increases at a constant rate even at a very low pressure change of 20 Pascal. The flexible bimodal sensor100according to an exemplary embodiment has a very high sensitivity at a low pressure, and thus, may be used for measuring bio information (e.g., blood pressure, heart rate, etc.).

FIG. 4is a graph showing a comparison of sensitivity between a sensor of the related art and a flexible bimodal sensor according to an exemplary embodiment. The sensor of the related art is different from the flexible bimodal sensor100according to the exemplary embodiment in that a gate insulating layer of the sensor of the related art has a flat panel shape without protrusions. In order to measure a drain current, a source is connected to a ground voltage, a voltage of −20 V is applied to the drain, and an alternate current having amplitude of 20 V and 0.3125 Hz is applied to the gate electrode160. Pressure increases from 10 kPa to 100 kPa.

Referring toFIG. 4, a regression value of plotting data P1measured by using a sensor of the related art is 0.003 kPa−1and a regression value of plotting data P2measured by using a flexible bimodal sensor100according to the exemplary embodiment is 0.028 kPa−1. That is, it is known that the pressure sensitivity of the flexible bimodal sensor100according to the exemplary embodiment is approximately 10 times greater than that of the sensor of the related art. Thus, it is understood that, in the flexible bimodal sensor100according to the exemplary embodiment, deformation of protrusions having a 3D microstructure is further increased according to the change of pressure, and thus, the pressure sensitivity is increased.

FIG. 5is a graph showing a pulse wave measured by using the flexible bimodal sensor100according to an exemplary embodiment. The gate insulating layer150is formed of P(VDF_TrFE), and the channel layer130is formed of pentacene.

Referring toFIG. 5, in a state that the flexible bimodal sensor100is disposed on a radial artery of a wrist, the flexible bimodal sensor100detects pressure caused by a pulse wave, and accordingly, a drain current is changed. Referring toFIG. 5, a pulse wave of a drain current has the same shape as a general pulse wave. That is, a measured single pulse wave shows a typical arterial pulse waveform. From the data ofFIG. 5, the pulse frequency of an object is approximately 82.

Hereinafter, a method of simultaneously measuring a temperature and pressure by using an alternating current (AC) bias measuring method will be described when two physical stimulations, for example, temperature and pressure are simultaneously applied to the flexible bimodal sensor100according to an exemplary embodiment.

A temperature and pressure are measured by using a matrix of measured signal values, for example, drain values.

First, changed values of μC and Voare measured. A relationship between the measured values and a temperature and pressure to be measured is expressed as Equation 1.

Here, μC is channel trans-conductance gm. Vois a voltage remaining in a ferroelectric gate insulating layer when a voltage applied to the ferroelectric gate insulating layer is removed. Vois also referred to as an equilibrium voltage. M1and M2respectively are a piezoresistance coefficient and a thermal resistance coefficient of the pentacene channel. M3and M4respectively are a piezoelectric coefficient and a pyroelectric coefficient of a ferroelectric P(VDF_TrFE). When the inverse matrix is used to obtain a temperature T and a pressure P, the equation of Equation 2 below is obtained.

The memory may store at least one of Equations 1 and 2. Further, the memory may store the piezoresistance coefficient M1, thermal resistance coefficient M2, the piezoelectric coefficient M3, and the pyroelectric coefficient M4. When the channel trans-conductance value μC and the equilibrium voltage Voare measured, the processor may retrieve Equation 1 or 2 from the memory, and may determine the temperature T and the pressure P based on the retrieved Equation 1 or 2.

Accordingly, the variation magnitudes of the temperature and pressure may be extracted from the variations of the measured drain currents according to the characteristics of a field effect transistor.

FIG. 6is a schematic plan view of a flexible bimodal sensor array according to an exemplary embodiment.

Referring toFIG. 6, a plurality of flexible bimodal sensors102are arranged in a matrix type on a flexible substrate210. As an example,FIG. 6shows the flexible bimodal sensors102arranged in a 4×4 matrix type. The structure of each of the flexible bimodal sensors102may be substantially the same as that of the flexible bimodal sensor100, and thus, the explanation thereof will not be repeated.

FIG. 7illustrates graphs for explaining an operation of flexible bimodal sensor array according to an exemplary embodiment. The flexible bimodal sensor array according to the current exemplary embodiment respectively include flexible bimodal sensors disposed in a 4×4 matrix on a flexible substrate.

Referring to graph (a) ofFIG. 7, temperatures and pressures that are measured by using the flexible bimodal sensor array are uniform in each of the flexible bimodal sensors.

Referring to graph (b) ofFIG. 7, temperatures and pressures are measured by the flexible bimodal sensors on which a material of 40° C. is placed. As shown in the graph (b), the temperatures and pressures increase.

Referring to graph (c) ofFIG. 7, when the temperatures and pressures are measured after cooling the material placed on the flexible bimodal sensor array for 30 minutes, the pressures become similar to of the pressures in graph (b), but the temperatures become lowered.

From the results ofFIG. 7, it may be understood that the flexible bimodal sensor array according to the current exemplary embodiment simultaneously measures temperatures and pressures.

FIG. 8is a schematic cross-sectional view of a flexible bimodal sensor300including microstructure according to another exemplary embodiment. Like reference numerals or names are used to indicate elements that are substantially identical to the elements of the flexible bimodal sensor100ofFIG. 1, and thus the detailed description thereof will not be repeated.

Referring toFIG. 8, the flexible bimodal sensor300includes a gate electrode360formed on a flexible substrate310. A gate insulating layer350is formed on the gate electrode360. The gate insulating layer350includes a base352having a predetermined thickness and a plurality of protrusions154extending from the base352toward the flexible substrate310and the gate electrode360. The protrusions354may be in contact with the flexible substrate310and the gate electrode360. A channel layer330is formed on the gate insulating layer350. A source electrode321and the drain electrode322are respectively formed on both edges of the channel layer330. An encapsulating layer340may be formed on the channel layer330. The encapsulating layer340may cover the channel layer330. The exemplary embodiment is not limited thereto. For example, the encapsulating layer340may also cover the source electrode321and the drain electrode322within the channel layer330.

InFIG. 8, the protrusions354of the gate insulating layer350are formed to be in contact with the gate electrode360and the flexible substrate310, but the current exemplary embodiment is not limited thereto. For example, the protrusions354may be formed to contact the channel layer330.

FIG. 9is a cross-sectional view of a microstructure of a flexible bimodal sensor according to another exemplary embodiment. Referring toFIG. 9, a gate insulating layer450of the flexible bimodal sensor includes a base452, a plurality of first protrusions453formed on a first surface452aof the base452, and a plurality of second protrusions454formed on a second surface452bof the base452. The second surface452bfaces the first surface452a.

The gate insulating layer150ofFIG. 1or the gate insulating layer350ofFIG. 8may be substituted by the gate insulating layer450.

The flexible bimodal sensor that employs the gate insulating layer450may have a larger deformation with respect to physical stimulations than the flexible bimodal sensors100or300, and thus, the sensitivity of the flexible bimodal sensor including the gate insulating layer450may be increased.

The flexible bimodal sensor according to the exemplary embodiments may have a high sensitivity to the extent that a human pulse wave can be measured, and two physical stimulations may be measured by using a single sensor. A plurality of flexible bimodal sensors may be disposed on a flexible substrate in an array, and the flexible bimodal sensor array may be applied to a wearable device or an electronic skin.