NON-INVASIVE SKIN SENSOR FOR LONG-TERM MONITORING AND METHOD FOR FABRICATING THE SAME

Embodiments relate to a non-invasive electronic device including at least one sensing unit capable of accurately monitoring a user's health condition for a long time such as a few weeks without malfunction while it is worn on the wearer's skin in a non-invasive manner and a method for fabricating the non-invasive electronic device. The non-invasive electronic device includes for example, a skin sensor device.

TECHNICAL FIELD

Embodiments of the present disclosure relate to a non-invasive electronic device, and more particularly, to a non-invasive electronic device with improved interface capable of preventing the accumulation of skin waste products and having high adhesion to skin and a method for fabricating the same.

BACKGROUND ART

Electronic skins (e-skins), which are electronic sensors mechanically affecting human skin, have been long developed as an ideal electronic platform for non-invasive human health monitoring irrespective of time and space. To achieve reliable health monitoring, interface between e-skin and skin needs to be compliant and invulnerable to damage. Non-patent Literature 1 (Rogers, J. A., Someya, T. & Huang, Y. Materials and mechanics for stretchable electronics. Science (80-.). 327, 1603-1607 (2010)) and Non-patent Literature 2 (Webb, R. C. et al. Ultrathin conformal devices for precise and continuous thermal characterization of human skin. Nat. Mater. 12, 938-944 (2013).) disclose electronic skins. However, the existing e-skins cannot perfectly permeate skin waste products, and thus the intimate interface degrades over time, which impedes accurate long-term health monitoring related to normal daily activities. Moreover, a high-performance single crystal semiconductor device is not embedded into an e-skin platform due to a thick and rigid substrate.

DISCLOSURE

Technical Problem

According to an aspect of the present disclosure, it is provided an electronic module for monitoring a user's skin condition.

Additionally, according to another aspect of the present disclosure, it is directed to providing a non-invasive electronic device for long-term monitoring, including the electronic module.

Besides, it is directed to providing a method for fabricating the electronic module or the non-invasive electronic device.

Technical Solution

An electronic module for monitoring a user's skin condition according to an aspect of the present disclosure may comprise a first passivation layer closer to the skin; an electronic circuit unit built on the first passivation layer, and including interconnects made of a conductive material and at least one sensing unit including a semiconductor property material, the sensing unit including at least one type of sensing unit of one or more of temperature sensing units; one or more of hydration sensing unit; one or more phot sensing units or one or more of strain sensing units; and a second passivation layer formed on the electronic circuit unit. Here, each of the first passivation layer, the electronic circuit unit and the second passivation layer includes a plurality of through-holes, and at least some of the plurality of through-holes of each of the first passivation layer, the electronic circuit unit and the second passivation layer form a hole pattern. Each of the hole pattern of the first passivation layer, the hole pattern of the electronic circuit unit and the hole pattern the second passivation layer has a planar pattern corresponding to each other to form an open channel when the first passivation layer, the electronic circuit unit and the second passivation layer are stacked.

In an embodiment, each of the plurality of through-holes may include each hole pattern formed by a plurality of dumbbell holes, each dumbbell hole is configured to connect between circular parts at two ends, and the plurality of dumbbell holes is arranged in an interdigitated array with respect to adjacent other dumbbell holes such that a circular part is adjacent to an extended part of the adjacent other dumbbell hole.

In an embodiment, each hole pattern may further include each of a plurality of circular holes, and each circular hole is formed in each sub region surrounded by the dumbbell holes arranged in the interdigitated array.

In an embodiment, some of the hole pattern of the first passivation layer, the hole pattern of the electronic circuit unit and the hole pattern of the second passivation layer may have respective specifications that are different from some other hole patterns.

In an embodiment, the temperature sensing unit may include a temperature responsive layer connected to the adjacent interconnect. Here, the temperature responsive layer generates an electric current in response to temperature, and the temperature responsive layer is connected to be positioned on a same plane as the adjacent interconnect.

In an embodiment, the temperature responsive layer may include a hole pattern formed by a plurality of through-holes, partially corresponding to the hole pattern of the first passivation layer and the hole pattern of the second passivation layer.

In an embodiment, the hydration sensing unit may include a plurality of electrodes connected to the adjacent interconnect—the plurality of electrodes including at least one first electrode and at least one second electrode; and a hydration responsive layer formed on a surface of the electrode. Each of the plurality of electrodes and the hydration responsive layer includes a plurality of through-holes that form an open channel when stacked upon each other. The through-holes of the electrodes and the through-holes of the hydration responsive layer have a planar shape corresponding to a planar shape of the through-holes of the first passivation layer and the second passivation layer at least in part.

In an embodiment, the hydration sensing unit may have a cantilever structure such that the first electrode of the hydration sensing unit extends from the interconnect of a first side, and the second electrode of the hydration sensing unit extends from the interconnect of a second side, and the extended parts of the at least one first electrode and the at least one second electrode are arranged in an interdigitated array.

In an embodiment, the photo sensing unit may include a photo responsive layer having two ends positioned on a surface of the adjacent interconnect, wherein the photo responsive layer generates an electric current in response to light irradiation, and the photo responsive layer generates the electric current when a specific band of light is irradiated, or generates the changed electric current when an intensity of the irradiated light changes.

In an embodiment, a part of the second passivation layer formed at a sensing area of the photo sensing unit may further include at least one auxiliary through-hole.

In an embodiment, the photo sensing unit may further include a capping layer formed at an interface between the part of the second passivation layer having the auxiliary through-hole and the photo sensing unit.

In an embodiment, the strain sensing unit may include an active layer having two ends positioned on a surface of the adjacent interconnect. Here, the active layer generates an electric current in response to strain of the electronic module.

In an embodiment, the strain sensing unit may further include at least one of a first capping layer formed at an interface between the active layer and the first passivation layer, or a second capping layer formed at an interface between the active layer and the second passivation layer.

In an embodiment, the electronic circuit unit may include a pair of strain sensing units. One of strain sensing units is positioned on the first passivation layer to sense x-axial strain, and the other strain sensing unit is positioned on the first passivation layer to sense y-axial strain.

A non-invasive electronic device according to another aspect of the present disclosure may comprise the electronic module according to the above mentioned embodiments. The non-invasive electronic device may comprise: a skin attachable flexible patch which contacts the first passivation layer, wherein the flexible patch includes a plurality of through-holes, and at least some of the plurality of through-holes of the flexible patch form a hole pattern, and the hole pattern of the flexible patch has a planar pattern corresponding to the hole pattern of the electronic module to form a perforated pattern when stacked with the electronic module.

In an embodiment, the plurality of through-holes of the flexible patch may include at least one specific through-hole that is different from the through-hole of the hole pattern. A size of the specific through-hole is different from a size of the through-hole that forms the hole pattern of the electronic module, and the photo sensing unit and the strain sensing unit are built in the specific through-hole.

In an embodiment, the flexible patch may further include a supporter which extends from one side to the other side in the specific through-hole to support the photo sensing unit.

A method for fabricating a non-invasive electronic device for long-term monitoring of a user's skin condition according to other aspect of the present disclosure may comprise forming a first sacrificial layer on a first substrate; building an electronic module on the first sacrificial layer; and removing the first sacrificial layer to separate the first substrate from the electronic module and bonding to a flexible patch. Here, the step of building the electronic module comprises patterning each layer in the electronic module to form an open channel running between a surface of the electronic module and an opposite surface.

In an embodiment, the step of building the electronic module may comprise forming a first passivation layer on the first sacrificial layer; building an electronic circuit unit on the first passivation layer; forming a second passivation layer on the electronic circuit unit; and patterning the first passivation layer and the second passivation layer stacked such that a plurality of through-holes is formed in the first passivation layer and the second passivation layer. Here, the plurality of through-holes of the first passivation layer and the second passivation layer form hole patterns corresponding to each other.

In an embodiment, building the electronic circuit unit may comprise building at least one sensing unit which senses a change in the skin condition—the sensing unit including at least one of a temperature sensing unit or a hydration sensing unit; and building interconnects connected to the sensing unit. Where building the interconnect comprises forming the interconnect made of a conductive material on the first passivation layer; patterning the interconnect to form a plurality of through-holes; and patterning the temperature sensing unit or the hydration sensing unit to form a plurality of through-holes. Here, the plurality of through-holes of the interconnect form a hole pattern, and the hole pattern of the interconnect partially corresponds to the hole pattern of the first passivation layer and the second passivation layer. The plurality of through-holes of the temperature sensing unit or the plurality of through-holes of the hydration sensing unit form a hole pattern, and the hole pattern of the temperature sensing unit or the hydration sensing unit corresponds to a sub pattern of the hole pattern of the first passivation layer and the second passivation layer at least in part. The sub pattern of the hole pattern of the first passivation layer and the second passivation layer is a pattern formed in a region that is different from a region corresponding to the hole pattern of the interconnect in the hole pattern of the first passivation layer and the second passivation layer.

In an embodiment, the first sacrificial layer may be removed through an electrochemical etching process. The separated first substrate is reused to fabricate other electronic module.

In an embodiment, the method may further comprise after removing the first sacrificial layer, cleaning off a residue of an etching solution remaining on a module structure from which the first substrate is separated.

In an embodiment, removing the first sacrificial layer and bonding to a flexible patch may include forming a second sacrificial layer on the surface of the electronic module; attaching a transferor onto the second sacrificial layer; and bonding the second sacrificial layer and the electronic module to a surface of the flexible patch through the transferor.

In an embodiment, the flexible patch bonded with the second sacrificial layer and the electronic module may be coated on a mold substrate. The mold substrate has a furrow pattern formed by a plurality of island steps, and each island step has a planar shape that matches each through-hole that forms the hole pattern of the flexible patch. In an embodiment, the bonding may comprise bonding such that each island step of the mold substrate corresponds to each through-hole of the electronic module.

In an embodiment, a size of the through-hole of the hole pattern of the flexible patch may be different from a size of the through-hole of the electronic module.

In an embodiment, bonding the second sacrificial layer and the electronic module to the surface of the flexible patch through the transferor may comprise separating the mold substrate from the flexible patch coated on the mold substrate, bonded with the electronic module through the transferor; separating the transferor in a state that the electronic module is bonded to the flexible patch; and removing the second sacrificial layer after separating the transferor.

In an embodiment, the transferor may be a thermal release tape (TRT). The transfer is detached by heating to being removed from the skin module.

In an embodiment, the second sacrificial layer may be made of a water-insoluble material that is different from the first sacrificial layer. The second sacrificial layer is removed through chemical etching.

In an embodiment, the method may further comprise cleaning off a residue of an etching solution or a surface residue from a structure of the skin sensor device from which the second sacrificial layer is removed.

Advantageous Effects

The electronic device according to an aspect of the present disclosure is noninvasively attached to a user's skin. The electronic device can accurately monitor the wearer's skin condition by at least one sensing unit in the device attached for a long time, for example, a few weeks without malfunction.

BEST MODE

The terms first, second and the like are used to describe a variety of portions, components, regions, layers and/or sections, but not limited thereto. These terms are used to distinguish a portion, component, region, layer or section from another. Accordingly, a first portion, component, region, layer or section described below may be referred to as a second portion, component, region, layer or section without departing from the scope of the present disclosure.

The term describing the relative space such as “below”, “on” or the like may be used to describe a relationship of an element to another shown in the drawing more easily. These terms are intended to include the intended meaning in the drawing as well as other meanings or operations of the device in use. For example, when a device in the drawing is inverted, elements described as being “below” other elements are described as being “on” them. Accordingly, the term “below” taken as an example include up and down directions. The device may rotate 90° or at any other angle, and the term describing the relative space is interpreted accordingly.

When an element is referred to as being “on” another element, the element may be on the other element, or intervening elements may be interposed between. In contrast, when an element is referred to as being “directly on” another element, there is no intervening element between them.

As used herein, the singular forms are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term “comprising” when used in this specification, specifies the presence of stated features, regions, integers, steps, operations, elements and/or components, but does not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements and/or components.

The terms as used herein are provided to refer to specific embodiments, but not intended to limit the present disclosure.

A non-invasive electronic device according to embodiments of the present disclosure includes an electronic module30that can operate on a user's skin. The electronic device is a non-invasive electronic device that can be attached to the user's skin. In certain embodiments, when the non-invasive electronic device includes at least one sensing unit to sense a change in the condition of the skin to which the electronic module is attached, it can be used as a sensor device (hereinafter, “skin sensor device”) attached to the user's skin to monitor the user's skin condition. In the specification, the electronic module including the sensing unit may be referred to as a sensor module.

Hereinafter, the non-invasive electronic device according to the present disclosure is described with regard to the certain embodiments in which the non-invasive electronic device includes the electronic module30(hereinafter, “the sensor module30”) including the sensing unit and operates as a skin sensor device, but this is for clarity of description only. It will be clearly understood by those skilled in the art that the embodiments of the present disclosure are not necessarily limited to the embodiments in which the electronic module of the present disclosure includes the sensing unit, or the non-invasive electronic device of the present disclosure is used as the skin sensor device.

FIG. 1is an exploded perspective view of a skin sensor device according to an aspect of the present disclosure, andFIG. 2is an image of the skin sensor device ofFIG. 1attached to a user's skin.

Referring toFIGS. 1 and 2, the skin sensor device1includes a sensor module30and a flexible patch60.

The skin sensor device1is fixed on the user's skin by the flexible patch60. The flexible patch60supports the sensor module30and fixes the position of the sensor module30close to the skin.

The flexible patch60has a sufficient thickness to support the weight of the sensor module30. For example, the flexible patch60may be 20 um in thickness.

Additionally, the flexible patch60comes into contact with the skin to attach the skin sensor device1to the skin. The flexible patch60is configured such that at least one surface has sufficient viscosity to attach to the skin.

The flexible patch60is made of a material with flexibility and adhesion properties. The flexible patch60may be made of, for example, a material including polydimethylsioxane (PDMS), but is not limited thereto.

As described above, the flexible patch60needs to have adhesion properties, and at the same time, have a supporting structure.

FIG. 3is a cross-section view of the flexible patch60of a bi-layer structure having different rigidity according to an embodiment of the present disclosure.

Referring toFIG. 3, the flexible patch60may have a bi-layer structure including two sub layers (hereinafter, a first flexible layer61and a second flexible layer62) having different rigidity. When rigidity is different, the elastic modulus of each sub layer61,62may be different.

The first flexible layer61is a sub layer that contacts the skin, and the flexible patch60is attached to the skin by the first flexible layer61.

The second flexible layer62is formed on the first flexible layer61. The second flexible layer62has higher rigidity than the first flexible layer61to support the integrated components (for example, the sensor module30, etc.) on the flexible patch60and appropriately control the bending of the flexible patch60so as to make handling easier. The second flexible layer62having higher rigidity may have lower elastic modulus than the first flexible layer61, and in turn, has weaker adhesion strength to the skin.

In contrast, the first flexible layer61that is attached to the skin is softer than the second flexible layer62having weaker adhesion strength to the skin. The first flexible layer61has lower flexural rigidity D1than the flexural rigidity D2of the second flexible layer62. For example, the first flexible layer61may have lower elastic modulus E1(for example, 0.04 MPa) to achieve conformal attachment to the skin surface, and the second flexible layer62may have higher elastic modulus E2(for example, 1 MPa).

In an embodiment, the flexible patch60may be made of off-stoichiometric PDMS to have higher adhesion strength and lower elastic modulus. The off-stoichiometric PDMS includes a pre-polymer and a curing agent.

The first flexible layer61and the second flexible layer62may include the pre-polymer and the curing agent. Here, the second flexible layer62may be configured to have a higher ratio of the curing agent than the first flexible layer61.

In an example, the first flexible layer61may include the pre-polymer and the curing agent at a 40:1 ratio, and the second flexible layer62may include the pre-polymer and the curing agent at a 10:1 ratio. Due to this difference in the ratio of the curing agent, the flexural rigidity D of the first flexible layer61and the second flexible layer62is differently determined.

Additionally, the flexible patch60has a perforated pattern formed by a plurality of through-holes. By the perforated pattern of the flexible patch60, the skin sensor device1has stronger adhesion, higher air permeability and stronger durability. The perforated pattern will be described in more detail below with reference toFIGS. 8 to 12.

The sensor module30may include an electronic circuit unit300; and a first passivation layer200and/or a second passivation layer400. In certain embodiments, the sensor module30may include the first passivation layer200and the second passivation layer400to protect the electronic circuit unit300.

The passivation layers200,400protect the electronic circuit unit300from an external environment by preventing the exposure of the electronic circuit unit300.

The first passivation layer200is a protective layer interposed between the flexible patch60and the electronic circuit unit300. When the skin sensor device1is attached to the skin, the first passivation layer200is disposed at a lower position than the second passivation layer400with respect to the skin surface, so it is may be herein referred to as a lower passivation layer. Under this attachment structure, the first passivation layer200is positioned below the electronic circuit unit300.

The first passivation layer200prevents the direct contact of the electronic circuit unit300with the flexible patch60. Additionally, the first passivation layer200prevents damage of the electronic circuit unit300(especially, the lower end of the unit) in the process of fabricating the sensor module30. For example, as described below with reference toFIG. 29I, the first passivation layer200prevents damage of the electronic circuit unit300in the process of removing a first sacrificial layer110.

The second passivation layer400is a protective layer positioned on the electronic circuit unit300. When the skin sensor device1is attached to the skin, the second passivation layer400is disposed at a higher position than the first passivation layer200with respect to the skin surface, so it may be herein referred to as an upper passivation layer. The second passivation layer400is formed on the surface of the electronic circuit unit300to cover the electronic circuit unit300and prevent the exposure of the electronic circuit unit300. The second passivation layer400may have a larger area than the electronic circuit unit300. The second passivation layer400may have a region that covers the electronic circuit unit300and other region that does not cover the electronic circuit unit300and covers the underlying component (for example, the first passivation layer200).

Additionally, the second passivation layer400not only prevents the exposure of the electronic circuit unit300but also keeps the position of the electronic circuit unit300near a Nature Machine Plane (NMP) of the skin sensor device1. Accordingly, the mechanical robustness of the skin sensor device1is improved.

The passivation layers200,400may be made of a material including polyimide (PI) and epoxy, but is not limited thereto. The passivation layers200,400may be made of the same material or different materials.

The passivation layers200,400may have the same thickness, or different thicknesses.

For example, the passivation layers200,400may have the thickness of 2 um and Young's modulus of 2.8 GPa.

Additionally, when the passivation layers200,400are stacked upon each other, each includes a plurality of through-holes to form a perforated pattern. The plurality of through-holes for each layer may form a pattern of a specific array structure. The planar structure of the hole patterns of the passivation layers200,400will be described in more detail below with reference toFIGS. 8 to 12.

The electronic circuit unit300is an electronic circuit including a device unit which operates to perform the monitoring function of the sensor module30. The electronic circuit unit300includes interconnect301and at least one device unit.

The interconnect301is a circuit component used to implement the electronic circuit, and is configured to allow the flow of electric current outputted from the device units (for example, a sensing unit) of the electronic circuit unit300. The interconnect301may be connected to the electrodes of the sensing unit to transmit the electric current outputted from the electrodes.

The interconnect301is positioned on the surface of the flexible patch60. When the sensor module30includes the first passivation layer200, the interconnect301may be positioned on the first passivation layer200.

The interconnect301may be formed in some or all of regions in which the device unit(s) are not disposed in the corresponding layer. For example, the interconnect301may be formed to connect regions I, II, III, IIII ofFIG. 1in which the sensing unit is positioned.

The interconnect301is made of a conductive material. The interconnect301may be made of, for example, a material including Au, but is not limited thereto.

The sensing unit is a device unit installed on the first passivation layer200, and includes a material having semiconductor properties. The sensing unit may generate the electric current in response to a change in the skin itself or the surrounding environment. The sensing unit may be used to monitor the skin condition. The generated electric current (for example, the variable electric current) flows from the sensing unit310,320,330,340to an analyzer (not shown) through the interconnect301.

In the certain embodiments, the sensor module30may include a temperature sensing unit310; a hydration sensing unit320; a photo sensing unit330and/or a strain sensing unit340to sense strain on the attached skin. When the electronic circuit unit300includes the sensing unit, the sensor module30may perform the operation of sensing a change in the user's skin condition, and the skin sensor device1may be used to obtain temperature information, moisture information and strain information of the skin and/or light information.

The at least one sensing unit310,320,330,340may be distributed in different regions on the NMP surface of the sensor module30according to the type. For example, as shown inFIG. 2, the temperature sensing unit310may be built in region2, the hydration sensing unit320may be built in region3, the photo sensing unit330may be built in region4, and the strain sensing unit340may be built in region5.

The temperature sensing unit310senses the temperature of the attached skin. The temperature sensing unit310may generate the changed electric current in response to a change in the temperature of the attached skin. The skin sensor device1may measure the user's skin temperature by the sensor module30including the temperature sensing unit310.

FIG. 4is a schematic cross-sectional view of the temperature sensing unit according to an embodiment of the present disclosure.

Referring toFIG. 4, the temperature sensing unit310may include a temperature responsive layer317.

The temperature responsive layer317is made of a material that changes in semiconductor properties in response to a change in temperature. The change in semiconductor properties is represented as a change in electric current, resistance, or other electricity related properties. The temperature responsive material may include, for example, Pt, but is not limited thereto.

The temperature sensing unit310may generate the electric current in response to the temperature by the temperature responsive layer317. As the temperature responsive layer317changes in electrical properties in response to a change in temperature, the temperature sensing unit310may generate the electric current that changes in response to a change in temperature.

The temperature responsive layer317is connected to the interconnect301positioned near the temperature sensing unit310. Some or all of the edges of the temperature responsive layer317having a predetermined area may be connected to the adjacent interconnect301. The connected part of the adjacent interconnect301may act as the electrode of the temperature sensing unit310.

In an embodiment, the temperature responsive layer317may be connected to be positioned on the same plane as the interconnect301. The temperature sensing unit310is a planar structure integrally formed with the interconnect301, and the planar part of the temperature sensing unit310and the planar part of the interconnect301may be implemented as layers of the electronic circuit unit300made of different materials.

Here, being positioned on the same plane represents that the temperature responsive layer317is not connected on the surface of the adjacent interconnect301and is positioned on the same plane. Being positioned on the same plane encompasses that a step is formed on the upper surface due to different thicknesses when the interconnect301and the temperature responsive layer317are positioned on the same plane.

At least some (for example, one end and/or the other end) of the edges of the temperature responsive layer317may be directly connected to the side of the interconnect301positioned on the first passivation layer200. Thus, the temperature responsive layer317is positioned on the same plane as the interconnect301(the surface of the first passivation layer200).

The electric current generated by the temperature responsive layer317is transmitted to the analyzer (not shown) through the connected interconnect301.

In some embodiments, the temperature responsive layer317may be formed with a different thickness from the adjacent interconnect301. For example, when the temperature responsive layer317is a Pt layer and the interconnect301is an Au layer, the thickness of the Pt layer317may be 35 nm to 45 nm, for example, approximately 40 nm, and the thickness of the Au layer301may be 95 nm to 105 nm, for example, approximately 100 nm.

In some other embodiments, the temperature sensing unit310may be formed with the same thickness as the interconnect301. For example, the temperature responsive layer317and the interconnect301may have the thickness of 100 nm.

Additionally, when some or all of the interconnects301are stacked with the other components60,200,400, each includes a plurality of through-holes to form a perforated pattern. The plurality of through-holes formed in the interconnect301may form a pattern of a specific array structure corresponding to the hole patterns of the other components. The hole pattern of the interconnect301will be described in more detail below with reference toFIG. 4, etc.

The hydration sensing unit320senses moisture in the attached skin. The hydration sensing unit320may generate the changed electric current in response to a change in moisture in the attached skin. The skin sensor device1may measure the amount of moisture of the user by the sensor module30including the hydration sensing unit320.

FIG. 5is a schematic cross-sectional view of the hydration sensing unit according to an embodiment of the present disclosure.

Referring toFIG. 5, the hydration sensing unit320is positioned between the interconnects301. The hydration sensing unit320includes a plurality of electrodes321,322and a hydration responsive layer327.

The plurality of electrodes includes at least one electrode321and at least one electrode322. The electrode321is connected to one interconnect301, and the electrode322is connected to the other interconnect301.

The electrodes321,322have such a cantilever structure that one end is connected to the interconnect301and extends to the other side from the connected interconnect301. The edges of a board extended from the electrodes321,322may extend across the planar part of the dumbbell hole (for example, the edge surrounding the dumbbell hole) of the first passivation layer.

In certain embodiments, a set of the plurality of electrodes may include a subset of the plurality of electrodes321and another subset of the plurality of electrodes322. The plurality of electrodes321,322may be built with an interdigitated electrodes structure. The extended parts (i.e., the board) of the cantilever of the electrodes321,322in the hydration sensing unit320are arranged in an interdigitated array. The board of the electrode322is positioned near the board of the electrode321.

In an embodiment, the width of the extended board of the electrode321or the width of the extended board of the electrode322may be equal to the distance between the adjacent electrodes321,322arranged in an interdigitated array.

For example, as shown inFIG. 5, the interspacing of the board of the electrode321, the board of the electrode322and the electrodes321,322may be 200 um.

In an embodiment, the electrodes321,322may be formed with the same thickness as the interconnect301. For example, the electrodes321,322and the interconnect301may have the thickness of 100 nm.

The hydration responsive layer327is formed on the surface of the electrodes321,322. The hydration responsive layer327includes a material that changes in semiconductor properties in response to a change in hydration. The change in semiconductor properties is represented as a change in electrical properties such as electric current properties. The hydration responsive material may include, for example, Pt, Cr and/or Au, but is not limited thereto.

The hydration responsive layer327may have a smaller thickness than the electrodes321,322. For example, when the electrodes321,322are 100 nm in thickness, the hydration responsive layer327may be 0.5 nm to 1.5 nm, for example, approximately 1 nm in thickness. However, this is provided by way of illustration, and the thickness of the electrodes321,322is not limited thereto.

The hydration responsive layer327may generate the electric current in response to moisture. The hydration responsive layer327may generate the changed electric current in response to a change in skin moisture or ambient moisture. The generated electric current is transmitted to the analyzer (not shown) through the electrodes321,322and the interconnect301.

Additionally, each of the electrodes321,322and the hydration responsive layer327includes a plurality of through-holes. The electronic circuit unit300including the hydration sensing unit320forms a perforated pattern when stacked with the other components60,200,400. In certain embodiments, some or all of the plurality of through-holes of the electrodes321,322and the hydration responsive layer327may form a pattern of a specific array structure corresponding to the hole patterns of the other components60,200,400at least in part. The hole pattern and the planar structure of the hydration sensing unit320will be described in more detail below with reference toFIG. 11, etc.

The photo sensing unit330senses light irradiated on the attached skin. The photo sensing unit330may generate the changed electric current in response to a change in light irradiated on the attached skin. The skin sensor device1may sense whether light is irradiated on the user's skin by the sensor module30including the photo sensing unit330and the band of the irradiated light, or may measure the intensity of the irradiated light.

FIG. 6is a schematic cross-sectional view of the photo sensing unit according to an embodiment of the present disclosure.

Referring toFIG. 6, the photo sensing unit330may include a photo responsive layer337.

The photo responsive layer337is made of a material that changes in semiconductor properties in response to light irradiation. For example, the photo responsive layer337may be made of a semiconductor material having band gap energy corresponding to a specific frequency band. When a specific frequency band of light is irradiated, the photo responsive material changes in electrical properties (for example, semiconductor properties) in response to the irradiated light.

In an embodiment, the photo responsive material may be a material having a band gap included in the specific frequency band. Here, the specific frequency band may be all or part of the ultraviolet (UV) band. For example, the frequency band to which the photo responsive semiconductor material responds is a range of frequencies converted to wavelengths of 400 nm or 380 nm or less.

The photo responsive material that responds to the above-described specific frequency band may include, for example, ZnO, AlN and/or GaN. The photo responsive material may have a monocrystalline or polycrystalline structure. For example, the photo responsive layer337may be made of polycrystalline ZnO.

ZnO and GaN have band gap energy (i.e., approximately 3.4 eV) corresponding to the frequency that is converted to approximately 365 nm wavelength. Accordingly, the sensor module30having the photo responsive layer made of ZnO and GaN may be used as a UV light sensor.

However, the photo responsive material is not limited to the above-described materials, and may be any other piezoelectric material and any other light active material.

The photo sensing unit330generates the electric current in response to to light irradiation on the photo responsive layer337. The photo sensing unit330may generate the changed electric current in response to a change in light irradiation.

When the specific band of light is irradiated, the photo responsive layer337may generate the electric current in response to the irradiated light, and/or the photo responsive layer337may generate the change electric current when the intensity of the irradiated light changes.

The photo responsive layer337is connected to the interconnect301positioned near the photo sensing unit330. One end and the other end of the photo responsive layer337having a predetermined area may be connected to the adjacent interconnect301. The connected part of the adjacent interconnect301may act as the electrode of the photo sensing unit330.

In an embodiment, the two ends of the photo responsive layer337may be connected on the surface of the adjacent interconnect301. The photo responsive layer337may be built with a free-standing structure that the two ends are supported by the electrode part of the interconnect301.

The generated electric current is transmitted to the analyzer (not shown) through the interconnect301.

In an embodiment, the sensor module30may include the second passivation layer400having at least one auxiliary through-hole401in an area that covers the photo sensing unit330.

The auxiliary through-hole401is part of the second passivation layer400, and may be formed in a sensing area of the photo sensing unit330. The sensing area is an area range in which light can directly travel to the photo responsive layer337in the absence of the second passivation layer400. For example, the auxiliary through-hole401may be formed in part of the second passivation layer400that covers the photo responsive layer337of the temperature sensing unit330.

In a situation in which the second passivation layer400absorbs some or all of the specific frequency band of light to which the photo responsive material responds, when the photo responsive layer337of the photo sensing unit330is entirely covered with the second passivation layer400, the photo sensing unit330may not detect a signal for the irradiated light. However, when the second passivation layer400has the auxiliary through-hole401as shown inFIG. 6, the photo responsive layer337may be optically exposed to the outside, and eventually the sensor module30may detect the specific signal corresponding to the specific frequency band more stably.

When the auxiliary through-hole401is formed in the second passivation layer400part on the photo sensing unit330, light can directly travel to the photo responsive layer337through the cavity of the auxiliary through-hole401. Light is directly irradiated on the photo responsive layer337through the auxiliary through-hole401. Accordingly, the photo sensing unit330has more sensitive light sensing performance.

In an embodiment, the photo sensing unit330may further include a capping layer338formed on the photo responsive layer337. The capping layer338is positioned at the interface between the photo responsive layer337and the second passivation layer400.

The capping layer338is made of a transparent material to allow light having passed through the auxiliary through-hole401to travel to the photo responsive layer337without interruption.

Additionally, the capping layer338prevents chemical damages of the photo responsive layer337caused by the contact of an external material with the photo responsive layer337through the auxiliary through-hole401.

The capping layer338may be made of, for example, a material including HfO2, Si3N4, SiNx or a combination thereof, but is not limited thereto.

In an embodiment, the photo sensing unit330may be built across one end and the other end of the specific through-hole of the flexible patch60. For example, one end of the photo sensing unit330may be positioned on part of the flexible patch60surrounding the specific through-hole of the flexible patch60, and the other end of the photo sensing unit330may be positioned on the opposite part of the flexible patch60. The specific through-hole is a through-hole having a planar shape and/or size that is different from each perforation of the perforated pattern formed by the stack of the hole patterns for each layer of the skin sensor device1.

In an embodiment, the flexible patch60may be formed such that its part is positioned across the specific through-hole. Thus, the photo sensing unit330may be built on the part of the flexible patch60positioned across the specific through-hole. The photo sensing unit330may be supported by the part of the flexible patch60positioned across the specific through-hole.

The planar structure of the photo sensing unit330will be described in more detail below with reference toFIGS. 16 and 30.

The strain sensing unit340senses strain of the attached skin. The strain sensing unit340may generate the changed electric current in response to the strain of the attached skin.

FIG. 7is a schematic cross-sectional view of the strain sensing unit according to an embodiment of the present disclosure.

Referring toFIG. 7, the strain sensing unit340may include an active layer347.

The active layer347is made of a material that changes in semiconductor properties in response to strain. A change in semiconductor properties is represented as a change in electric current, resistance or other electricity related properties. With the semiconductor properties, the generation of the electric current is activated when strain is applied to the sensor module30(or the skin sensor device1). The strain responsive material having the semiconductor properties may be a material that has good electron transport characteristics and may be used as a piezoelectric material. For example, the strain responsive material may be a material including ZnO, AlN, GaN or a combination thereof, but is not limited thereto, and may be any other piezoelectric material.

The strain sensing unit340generates the electric current in response to the strain of the skin sensor device1. When strain is applied to the skin to which the skin sensor device1is attached, the strain is also applied to the active layer347. For example, the structure of the active layer347may change depending on the skin strain. Thus, the strain sensing unit340may generate the changed electric current in response to a change in the strain of the active layer347.

The active layer347is connected to the interconnect301positioned near the strain sensing unit340. One end and the other end of the active layer347having a predetermined area may be connected to the adjacent interconnect301. The connected part of the adjacent interconnect301may act as the electrode of the strain sensing unit340.

In an embodiment, the two ends of the active layer347may be connected on the surface of the adjacent interconnect301. The active layer347may be built with a free-standing structure that the two ends are supported by the electrode part of the interconnect301.

The generated electric current is transmitted to the analyzer (not shown) through the interconnect301.

The strain sensing unit340is encapsulated with the upper/lower passivation layers200,400and the unit is positioned close to the neutral mechanical plane (NMP). Accordingly, the mechanical robustness of the sensor module30is improved.

In an embodiment, the strain sensing unit340may further include a bottom capping layer346and/or a top capping layer348. The bottom capping layer346and the top capping layer348are an interfacial layer which is inserted into the interface between the active layer347and the passivation layers200,400. As shown inFIG. 7, the bottom capping layer346is positioned below the active layer347. The top capping layer348is positioned on the active layer347.

The bottom capping layer346is inserted into the electrodes341,342of the active layer347/the interconnect301to form a Schottky barrier for allowing the strain sensing unit340to use the piezoelectric effect.

The top capping layer348is formed on the strain sensing unit340, and protects the strain sensing unit (for example, the active layer347) in the subsequent process.

The thickness of the bottom capping layer346and the top capping layer348may be different. For example, the top capping layer348may be 2.5 nm to 3.5 nm, for example, approximately 3 nm in thickness. The bottom capping layer346may be 1 nm to 2 nm, for example, approximately 1.5 nm in thickness.

The bottom capping layer346and/or the top capping layer348may be made of a material including HfO2, Si3N4, SiNx, epoxy resin or a combination thereof, but is not limited thereto, and may be made of any other resin material.

In an embodiment, the strain sensing unit340may be built across one end and the other end of the specific through-hole of the flexible patch60. For example, one end of the strain sensing unit340(for example, the active layer347) is positioned on part of the flexible patch60disposed around the specific through-hole of the flexible patch60, and the other end of the strain sensing unit340(for example, the active layer347) may be positioned on the other part opposite the part of the flexible patch60. The specific through-hole is a through-hole having a planar shape and/or size that is different from each perforation of the perforated pattern formed by the stack of the hole patterns for each layer of the skin sensor device1.

In an embodiment, the flexible patch60may be formed such that its part is positioned across the specific through-hole. Thus, the strain sensing unit340may be built on the part of the flexible patch60positioned across the specific through-hole. The strain sensing unit340may be supported by the part of the flexible patch60positioned across the specific through-hole.

In an embodiment, the strain sensing unit340may be positioned on the cavity formed in the specific through-hole. For example, as shown inFIG. 7, the stack of the first passivation layer200and the strain sensing unit340may be positioned across one end and the other end of the flexible patch60near the specific through-hole. As opposed to the photo sensing unit330, the strain sensing unit340may not be supported by the patch60. Accordingly, when the structure of the skin sensor device1changes due to skin strain, the strain may be applied to the strain sensing unit340more sensitively.

The specific through-hole in which the strain sensing unit340is built may be a specific through-hole that is the same as or different from the specific through-hole in which the photo sensing unit330is built. The photo sensing unit330and the strain sensing unit340may be configured to go across a same large through-hole, or each of the strain sensing unit340and the photo sensing unit330may be built in each specific through-hole disposed in different regions as shown inFIG. 2.

The planar structure of the photo sensing unit330and the strain sensing unit340will be described in more detail with reference to the followingFIGS. 16 and 17.

In an embodiment, the thickness of each layer60,200,310,320,330,340,400in the skin sensor device1is designed based on the material component of each layer and the following Equation:

H=?[Equation⁢1]?indicates text missing or illegible when filed

The above Equation 1 is an equation for calculating the height H of NMP present in the multi-stack structure having n layers. Here, the height H is the distance from the bottom of the multi-stack structure. Here, Eiand tiare the plane-strain coefficient and thickness of the ithlayer, and the bottom layer is i=1.

For example, in the region5in which the strain sensing unit340is built, the flexible patch60may be designed with the thickness of 20 um, the first passivation layer200with the thickness of 2 um, the electrodes341,342with the thickness of 100 nm, the bottom capping layer346with the thickness of 1.5 nm, the active layer347with the thickness of 100 nm, the top capping layer348with the thickness of 3 nm, the second passivation layer400with the thickness of 2 um, respectively, according to the above Equation 1. However, these values are provided by way of illustration, and the thickness of each layer of the skin sensor device1is not limited thereto.

In an embodiment, the skin sensor device1may further include an alignment key500for fixing the stack and connection of each component60,200,300,400. The alignment key500is implemented with a structure that is difficult for each component60,200,300,400to make planar rotation.

Additionally, the skin sensor device1may include a plurality of alignment keys500as shown inFIG. 2.

The sensor module30may include at least one sensing unit for each type. Each sensing unit obtains information of different directions and different regions.

In an embodiment, the sensor module30may include a pair of strain sensing units340. Here, one of strain sensing units340may be positioned to sense the x-axial strain of the NMP, and the other strain sensing unit340may be positioned to sense the y-axial strain of the NMP. For example, as shown inFIG. 2, the strain sensing units340may be positioned, for example, perpendicular to each other to obtain strain information of each direction, unique to the dimensional axis.

The components60,200,300,400stacked in the skin sensor device1have a plurality of through-holes. In each component60,200,300,400of the skin sensor device1, some or all of the plurality of through-holes may form a particular hole pattern in which specific through-holes are arranged repeatedly.

When the components60,200,300,400having the corresponding hole patterns are stacked upon each other to build the skin sensor device1, each specific hole pattern has a planar pattern structure corresponding to each other to form a perforated pattern passing through the cross section from one surface of the skin sensor device1to the other surface. For example, a hole pattern formed by at least some of the plurality of through-holes of the first passivation layer200, a hole pattern formed by at least some of the plurality of through-holes of the electronic circuit unit300, and a hole pattern formed by at least some of the plurality of through-holes of the second passivation layer400have planar patterns corresponding to each other to form open channels when the first passivation layer200, the electronic circuit unit300and the second passivation layer400are stacked.

In certain embodiments, the specific hole pattern is a hole pattern formed with an array structure having auxetic properties, and may be referred to as an auxetic hole pattern.

In general, the auxetic structure refers to a structure of which the dimension increases in a direction perpendicular to a first direction when subjected to a tensile force in the first direction. For example, in case that the auxetic structure may be described as having a length, a width and a thickness, when the auxetic structure is subjected to a tensile force in the vertical direction, its width increases. Additionally, the auxetic structure is bidirectional so that when stretched in the vertical direction, its length and width increases, and when stretched in the horizontal direction, its width and length increases, but its thickness does not increase. The auxetic structure has a negative poisson's ratio.

FIG. 8is a diagram showing the auxetic hole pattern according to an embodiment of the present disclosure.

Referring toFIG. 8, the auxetic hole pattern is a pattern structure in which dumbbell shaped through-holes (hereinafter, the “dumbbell holes”) and/or circular holes are arranged. For example, the auxetic hole pattern may be a pattern of arrangement of dumbbell holes and circular holes.

The dumbbell hole includes a circular part positioned at each of two ends and a central part connecting the circular parts. The width of the central part may be narrower than the diameter of each circular part.

In the auxetic hole pattern, the dumbbell hole is arranged in an interdigitated array with respect to the adjacent other dumbbell hole such that the circular part in the linear extension direction is close to the linear part of the other dumbbell hole. As shown inFIG. 8, each dumbbell hole has an interdigitated planar structure in which the connecting part of each dumbbell hole is positioned perpendicular to the connecting part of the adjacent dumbbell hole. Thus, hole pattern forms an auxetic hole pattern having auxetic properties.

The plurality of dumbbell holes arranged in an interdigitated array forms a hinge area between adjacent other dumbbell holes.

The auxetic hole pattern may further include a plurality of circular holes that may be formed in the remaining region in which the array of dumbbell holes is not formed. The remaining region is a sub region (the hinge area ofFIG. 8) surrounded by the interdigitated dumbbell holes. As shown inFIG. 8, each circular hole in the array of circular holes may be arranged such that it is surrounded by the circular part of the adjacent other dumbbell hole.

When the plurality of circular holes is added, the skin sensor device1having an auxetic perforated pattern by the stack of the auxetic hole patterns has improved air permeability.

In an embodiment, each circular hole of the array of circular holes may have a diameter that is different from that of the circular part of each dumbbell hole of the array of dumbbell holes. For example, each circular hole of the array of circular holes may be configured to have a smaller diameter than the circular part of each dumbbell hole of the array of dumbbell holes.

Additionally, each through-hole in the auxetic hole pattern may be distributed such that the interspacing between at least some holes is 60 μm or less. For example, the interspacing between all the through-holes of the auxetic hole pattern in the skin sensor device1may be 60 μm or less. Additionally, when an auxetic perforated pattern is formed by the stack of the auxetic hole patterns for each layer, each perforation in the auxetic perforated pattern may be distributed such that the interspacings between at least some perforations each other are 60 μm or less.

It is known that the area of the sweat pore has a diameter of 60 μm or more and an average diameter of 80 μm. Additionally, since the amount of waste products to be secreted and biological functions performed by sweat such as temperature control are different depending on skin location, sweat pores are arranged with different distribution densities depending on the body parts. For example, sweat pores are distributed with the density of 60 cm−2in the back, 400 cm−2in the palm, and 180 cm−2in the forehead.

When the interspacing between the through-holes is 60 μm or more, the surface of the flexible patch60near the holes may block the sweat pores at least in part. In contrast, the skin sensor device1having the hole interspacing of less than 60 μm may obtain higher air permeability (for example, almost 100% air permeability).

Each layer60,200,300,400that constitutes the skin sensor device1forms the auxetic hole pattern. The skin sensor device1is fabricated by stacking each layer60,200,300,400in a sequential order. Thus, perforations which are open channels through which a fluid flows may be built between the lowermost layer60of the skin sensor device1that contacts the skin and the uppermost layer400opposite the lowermost layer60.

The sidewall of each perforation in the perforated pattern of the skin sensor device1includes sidewalls of the through-holes of the auxetic hole patterns for each layer60,200,300,400. When the auxetic hole patterns for each layer200,300,400of the sensor module30are stacked, open channels that constitute some of the perforation sidewalls in the perforated pattern of the skin sensor device1are built.

FIG. 9is a schematic diagram of region1in which the interconnect301is built according to an embodiment of the present disclosure. InFIG. 9, the area that covers the interconnect301in the second passivation layer400is omitted.

Referring toFIG. 9, each of the flexible patch60, the first passivation layer200, the interconnect301and the second passivation layer400stacked in region1includes an auxetic hole pattern. The auxetic hole patterns for each layer60,200,301,400form an auxetic perforated pattern when stacked such that the through-holes correspond to each other.

The interconnect301of the auxetic hole pattern may be configured such that the pattern of the edge is connected to the auxetic hole pattern of the adjacent second passivation layer400.

FIG. 10is a schematic diagram of region2in which the temperature sensing unit310is built according to an embodiment of the present disclosure. InFIG. 10, the area that covers the temperature sensing unit310in the second passivation layer400is omitted.

Referring toFIG. 10, each to the flexible patch60, the first passivation layer200, the temperature sensing unit310and the interconnect301connected the temperature sensing unit310stacked in region2includes an auxetic hole pattern.

The temperature sensing unit310may be implemented as mesh construction of the auxetic hole pattern.

The auxetic hole pattern in the temperature sensing unit310(for example, the temperature responsive layer317) has a planar pattern partially corresponding to the hole pattern of the first passivation layer200and the hole pattern of the second passivation layer400. The entire auxetic hole pattern of the temperature sensing unit310may correspond to a sub pattern of the auxetic hole pattern of the passivation layers200,400.

The edge to be connected to the interconnect301in the auxetic hole pattern of the temperature sensing unit310may be implemented in a shape that completes an auxetic hole pattern when connected to the interconnect301.

FIG. 11is a plan view of region3in which the hydration sensing unit320is built according to an embodiment of the present disclosure. InFIG. 11, the second passivation layer400is omitted.

Referring toFIG. 11, the hydration sensing unit320includes an auxetic hole pattern. In certain embodiments, the electrodes321,322and the hydration responsive layer327include the auxetic hole pattern.

The auxetic hole pattern of the electrodes321,322and the auxetic hole pattern of the hydration responsive layer327correspond to each other. In an embodiment, the plane of the auxetic hole pattern of the electrodes321,322and the plane of the auxetic hole pattern of the hydration responsive layer327may match each other.

The plurality of through-holes that forms the auxetic hole pattern of the hydration sensing unit320(for example, the auxetic hole pattern of the electrodes321,322and the auxetic hole pattern of the hydration responsive layer327) has a planar shape corresponding to the planar shape of the through-holes in the hole pattern of the first passivation layer200and the hole pattern of the second passivation layer400, at least in part.

The auxetic hole pattern of the hydration sensing unit320includes through-holes corresponding to the entire planar shape of the through-holes of the other layers200,400. For example, as shown inFIG. 11, the circular holes arranged in parallel to the electrodes321,322are a sub pattern of the auxetic hole pattern of the other layers200,400, and correspond to the entire shape of the circular holes.

The auxetic hole pattern of the hydration sensing unit320includes through-holes corresponding to part of the shape of the through-holes of the other layers200,400. As shown inFIG. 11, the dumbbell holes included in the electrodes321,322have a planar shape formed by a portion of the circular part and its connected central part in the dumbbell holes of the other layers200,400. The dumbbell hole of the hydration sensing unit320partially corresponds to the planar shape of the dumbbell holes of the other layers200,400.

Additionally, the edges of the electrodes321,322and the hydration responsive layer327that form the edges of the cantilever in the hydration sensing unit320may have a planar shape corresponding to part of the shape of the through-holes of the other layers200,400. As shown inFIG. 11, a planar shape partially corresponding to the circular holes of the other layers200,400may be formed at the extended end.

When the electronic circuit unit300including the temperature sensing unit310and the hydration sensing unit320having the planar structure of the auxetic hole pattern is stacked with the flexible patch60, the first passivation layer200and the second passivation layer400having the corresponding auxetic hole pattern, a perforated pattern having the plane of the auxetic hole pattern is formed.

Due to the planar structure (for example, the mesh structure) of the auxetic hole pattern, the sensor module30may maintain the open channels that allow the skin to breathe in the region in which the temperature sensing unit310and/or the hydration sensing unit320are built.

Even though the hole pattern of the hydration sensing unit320partially corresponds to the hole pattern of the other layers200,400, a perforated pattern that act as open channels in the sensor module30and the skin sensor device1may be formed. The perforations in the perforated pattern can sufficiently act as open channels even though they are partially blocked. It is because the mesh of the hydration sensing unit320has a small width such as a few tens of nm to a few hundreds of nm.

In an embodiment, in the auxetic hole patterns for each layer that form the perforated pattern, the auxetic hole pattern of a layer may have respective specifications that are different from that of the auxetic hole pattern of the other layer. The specification of the auxetic hole pattern for each layer is based on the hole size and the hole interspacing.

FIGS. 12A to 12Care diagrams showing the auxetic hole pattern for each layer according to an embodiment of the present disclosure.

FIG. 12Ais a table showing the structural properties of the auxetic hole pattern for each specification, andFIG. 12Bis an image of the auxetic hole pattern for each layer having the specification selected from the table ofFIG. 12A.FIG. 12Cis a plan view of the skin sensor device1including the stack of the layers60,200,300,400having the specification of the auxetic hole pattern ofFIG. 12B.

The table ofFIG. 12Ais obtained under the fixed ratio of the diameter D of the circular part in the dumbbell hole, the auxetic cut width W and the radius R of the circular hole.

Since the material properties and/or purpose of each layer differ, the corresponding through-hole in the auxetic hole pattern for each layer may not match each other.

For example, the auxetic hole pattern of the flexible patch60may be designed with the specification D4of the table ofFIG. 12A. In contrast, the auxetic hole pattern of the passivation layer200,400may be designed with the specification D6of the table ofFIG. 12A. Additionally, the auxetic hole pattern of the electronic circuit unit300(for example, the Au interconnect301) may be designed with the specification D7of the table ofFIG. 12A.

The skin sensor device1having the planar structure of the auxetic hole pattern has the following advantages: a) high work of adhesion; b) high air permeability; c) high durability. Due to these advantages, the skin sensor device forms a highly conformal contact on the curved skin surface including wrist wrinkles.

FIG. 13is a diagram illustrating high work of adhesion of the skin sensor device according to an embodiment.

As the flexible patch60of the skin sensor device1is attachable, when the contact area of the flexible patch60with the skin increases, the work of adhesion of the skin sensor device1increases. Additionally, to implement the imperceptible skin sensor device1, it is necessary to minimize the areal density of the skin sensor device1. As the skin sensor device1is lighter in weight, the user does not recognize the fact that the skin sensor device1is attached to the user's skin, and the skin sensor device1does not delaminate from the skin.

Referring toFIG. 13, as each of the stack of the flexible patch60and the sensor module30has a larger number of perforations of the auxetic hole pattern, the areal mass density of the corresponding stack decreases and the work of adhesion increases.

As the perforation of the auxetic hole pattern is added to the stack, the mass of the space corresponding to the inner cavity of the perforation decreases. Additionally, it is because as the number of perforations increases, the interspacing between perforations decreases and the effective area that contacts the curved skin surface increases.

That is, the skin sensor device1has the perforated pattern of the auxetic hole pattern, thereby minimizing the weight load applied to the user's skin, and as a result, the skin sensor device1has high work of adhesion.

FIG. 14is a diagram illustrating high air permeability of the skin sensor device according to an embodiment.

As described above, the auxetic hole pattern of the skin sensor device1has the hole interspacing (for example, the hole interspacing of the flexible patch60) of 60 μm or less. As shown inFIG. 14, when the widest hole interspacing of the flexible patch60that contacts the skin is less than 60 μm, the skin sensor device1may have almost 100% air permeability.

FIGS. 15A to 15Bare diagrams illustrating high durability of the skin sensor device according to an embodiment.

FIG. 15Ashows a principal maximum strain distribution of global strain in a pattern formed by circular through-holes alone; a pattern formed by square through-holes alone (hereinafter, Auxetic kirigami pattern), and the auxetic hole pattern of the present disclosure.FIG. 15Ashows definite element analysis (FEA) results of the tensile properties up to the strain of 30% for each pattern.

The auxetic hole pattern generates elasticity while suppressing cracks caused by strain localization. The auxetic hole pattern is designed in a combined pattern of the auxetic kirigami pattern and the circular pattern to complement the disadvantages of the auxetic kirigami pattern and the circular pattern and provide their unique advantages.

Specifically, part corresponding to the auxetic kirigami pattern in the auxetic hole pattern provides extreme conformability on the bumpy skin surface due to the nonlinear elastic properties, while the other part corresponding to the circular pattern in the auxetic hole pattern provides open channels and lessens the local strain at the edge of the kirigami pattern part.

When the circular hole pattern model is stretched and a network placed in parallel to the axial direction is stretched, the entire structure becomes narrow in the lateral direction. When the auxetic bar pattern or dumbbell through-hole pattern is subjected to a tensile force, structural opening is formed before the material is stretched.

In the circular pattern, when deformation is applied, the square unit rotates and its connected hinge bends. The local deformation is generated at the hinge of the auxetic bar pattern. This is the disadvantage of the auxetic bar pattern which is vulnerable to a mechanical failure and may limit the engineering application program.

However, the auxetic hole pattern of the present disclosure solves the disadvantage at least in part.

As described above with reference toFIG. 8, the auxetic hole pattern formed in each layer include a square rotation unit connected by the hinges as well as dumbbell-shaped through-holes. The dumbbell pattern greatly reduces the strain occurring at the hinge. The C-shaped arc of the circular pattern effectively makes the sharp tip edge dull and finally reduces the strain level. For example, when the overall strain exceeds 15%, the structure of the dumbbell pattern is fully open and stretching of the material itself (i.e., the auxetic hole pattern itself) starts.

The strain delocalization greatly improves the mechanical reliability of the skin sensor as shown inFIG. 15B. Based on the results ofFIG. 15, it is obvious that the auxetic dumbbell hole design of the skin sensor that delocalizes the strain distribution can withstand the repeated mechanical strains on the skin during long-term monitoring.

Due to the advantage of the auxetic hole pattern structure, the skin sensor may be used to monitor the user's skin condition for a long time. In addition to the mechanical robustness and the skin-like mechanical properties, it is possible to prevent sensor malfunction caused by sweat accumulation, thereby achieving long-term skin condition monitoring without malfunction of the electronic module for at least 1-2 weeks.

Additionally, with the properties of the auxetic structure by the auxetic perforated pattern, the skin sensor device1has human skin-like nonlinear behavioral characteristics.

FIG. 15Bshows a stress-strain curve of the skin sensor device having the auxetic perforated pattern. According to the stress-strain curve, the skin sensor device1has non-linear mechanical behaviors, and the mechanical parameters have similar characteristics to the human skin. Accordingly, the skin sensor device1can be used as electronic skins (e-skins) that replace human skin in a variety of applications.

Meanwhile, the electronic circuit unit300may further include a unit having a planar structure that does not correspond to the auxetic hole pattern of the flexible patch60. In certain embodiments, the electronic circuit unit300may further include the photo sensing unit330and/or the strain sensing unit340. The photo sensing unit330and the strain sensing unit340may be built in the through-hole that is different from the auxetic hole pattern of the flexible patch60.

FIG. 16is a schematic diagram of region4in which the photo sensing unit is built according to an embodiment of the present disclosure.

Referring toFIG. 16, the photo sensing unit330may be built in the specific through-hole of the flexible patch60.

As described above with reference toFIG. 6, for the photo sensing unit330to perform a photo sensing operation, it is necessary to irradiate light on the surface of the photo responsive layer337. The photo responsive layer337has higher responsivity to light as the area of the plane is wider.

In case that an auxetic hole pattern is formed in the photo responsive layer337, the area decreases as much as the formed dumbbell/circular holes. Accordingly, the photo responsive layer337has lower need to form an auxetic hole pattern, and thus does not need to be built in the auxetic hole pattern of the flexible patch60.

The specific through-hole in which the photo sensing unit330will be built is a through-hole formed in a specific other region that is different from the region in which the auxetic hole pattern is formed, and is an unmatched through-hole having a size and/or shape that is different from the circular hole or dumbbell hole of the other region. For example, the photo sensing unit330may be built in the specific through-hole of the flexible patch60having a larger size than the dumbbell/circular hole of the auxetic hole pattern of the flexible patch60of the other region to form a perforated pattern.

In an embodiment, the flexible patch60that will be positioned at the lower end of the photo sensing unit330may further include a supporter630connecting two ends in the plane of the specific through-hole. As shown inFIG. 16, the supporter630connects one end and the other end of a large through-hole. The supporter630of the flexible patch60supports at least part of the photo sensing unit330.

In an embodiment, the second passivation layer400in contact with the photo sensing unit330may be configured to have a plurality of auxiliary through-holes401.

Each auxiliary through-hole401is a through-hole formed in the upper passivation layer400formed in the specific region, not the region in which the auxetic hole pattern formed in the upper passivation layer400is formed. By the opening401, the photo responsive layer337is not blocked all over the entire area by the upper passivation layer400, and is partially exposed.

The auxiliary through-hole401may be smaller in size than the though-hole that forms the auxetic hole pattern.

FIG. 17is a schematic diagram of region5in which the strain sensing unit is built according to an embodiment of the present disclosure.

Referring toFIG. 17, the strain sensing unit340may be built in the specific through-hole of the flexible patch60.

The specific through-hole in which the strain sensing unit340will be built is a through-hole formed in a specific other region that is different from the region in which the auxetic hole pattern is formed, and is an unmatched through-hole having a size and/or shape that is different from the circular hole or dumbbell hole of the other region. For example, the active layer347of the strain sensing unit340may be built in the specific through-hole of the flexible patch60having a larger size than the dumbbell/circular hole in the auxetic hole pattern of the flexible patch60of the other region for forming a perforated pattern as shown inFIG. 17.

The active layer347of the strain sensing unit340extends from the electrode341or342to the other electrode342or341. The strain sensing unit340has a suspended free-standing structure. For example, the active layer347may be implemented as a cantilever structure extended from the electrode341or342.

Part of the active layer347is positioned on the plane of the specific through-hole of the flexible patch60. The cavity may be an internal space surrounded by the sidewalls of the specific through-hole of the flexible patch60such as furrow. As opposed to the photo sensing unit330supported by the supporter630, the strain sensing unit340is not supported by the flexible patch60.

When strain occurs in the skin, part of the free-standing structure bends in the cavity formed by the sidewalls of the specific through-hole of the flexible patch60. All or part of a projection area of the bendable part in the free-standing structure may be included in the planar inner area of the specific through-hole.

The specific through-hole in which the strain sensing unit340is built may be different from the specific through-hole in which the photo sensing unit330is built. As shown inFIG. 2, the strain sensing unit340may be built in region5that is different from region4in which the photo sensing unit330is installed.

The skin sensor device1having the sensing unit310,320,330and/or340may have high adhesion, air permeability and durability, and obtain various types of skin related information skin such as temperature information, moisture information, light information and strain information of the skin.

FIGS. 18A to 18Dare partial enlarged views of regions2to5ofFIG. 2.FIGS. 19 to 22are diagrams illustrating the performance for each sensing unit included in the skin sensor device1ofFIG. 18. As shown inFIGS. 18A to 18D, when the sensor module30includes the sensing units310,320,330,340, the skin sensor device1may obtain information associated with the user's skin condition (the temperature information, hydration information, stain information and/or light information), in the regions2,3,4,5of the skin in which each sensing unit310,320,330,340is built.

FIG. 19shows the temperature sensing performance of the skin sensor device including the temperature sensing unit ofFIG. 18A.

As shown inFIG. 19, the temperature responsive layer317(for example, the Pt thin film layer) of the temperature sensing unit310changes in electrical properties such as resistance in response to a change in temperature around the skin. The temperature responsive layer317has the electrical properties that the resistance characteristics change with change in temperature. Using this predetermined correlation, the skin sensor device1may be used as a sensor device for monitoring temperature information.

FIG. 20shows the moisture sensing performance of the skin sensor device including the hydration sensing unit ofFIG. 18B.

FIG. 20is a graph obtained using the moisture sensing performance of the existing moisture sensor device (Courage Khazaka electronic Corneometer CM-825, Germany) and the skin sensor device1ofFIG. 18including the hydration sensing unit320. The moisture sensing performance of the existing moisture sensor device is indicated by a line, and the sensing results of the skin sensor device1including the hydration sensing unit320are indicated by points.

Referring toFIG. 20, the hydration responsive layer327(for example, the Pt thin film layer) of the hydration sensing unit320changes in capacitance values of the hydration sensing unit320in response to a change in hydration around the skin. The hydration responsive layer327has the electrical properties that the capacitance value change with change in moisture. Using this predetermined correlation, the skin sensor device1may be sufficiently used as a sensor device for monitoring moisture information. In particular, as shown inFIG. 20, the correlation of the hydration sensing unit320matches the performance trend of the existing hydration sensing device, and thus it is found that the skin sensor device1including the hydration sensing unit320has the equivalent sensing performance to the performance of the existing hydration sensing device.

FIGS. 21A to 21Cshow the UV sensing performance of the skin sensor device including the photo sensing unit ofFIG. 18C. The photo sensing unit330ofFIG. 18Cincludes a ZnO thin film as the photo responsive layer337.

FIG. 21Ashows the response of the photo sensing unit ofFIG. 18Cto a specific band of light.

Referring toFIG. 21A, the skin sensor device1including the photo sensing unit330may sense if light irradiated on the skin includes the UV band component. It is found that when light is irradiated on the skin, the responsivity and switching speed of the photo sensing unit330including the photo responsive layer337sharply changes in the specific wavelength band (for example, about 300 nm). Accordingly, when the responsivity and switching speed of the photo sensing unit330changes, the skin sensor device1may sense light irradiation on the skin.

FIG. 21Bshows electric current generation of the photo sensing unit ofFIG. 18Cas a function of light intensity.FIG. 21Cis a diagram illustrating the response speed of the photo sensing unit ofFIG. 18C.

Additionally, referring toFIGS. 21B and 21C, the skin sensor device1including the photo sensing unit330may measure the intensity of light irradiated on the skin. The photo sensing unit330may generate the electric current that changes as a function of the light intensity.

When UV light having the maximum UV peak wavelength of 304 nm is irradiated with the light intensity of 2.23-48.7 mW cm−2for approximately 10 seconds, the photo electric current of the photo sensing unit330changes as a function of the light intensity as shown inFIG. 21B. When the intensity of irradiated light differs, the photo electric current value also differs in response.

The responsivity of the skin sensor device1including the photo sensing unit330is extracted from the photo electric current change and the slope of a UV light intensity curve as indicated inFIG. 21C. Referring toFIGS. 21A to 21C, the responsivity of the skin sensor device1is 1.17 AW−1. The skin sensor device1having the device characteristics such as responsivity may be sufficiently used as a sensor device for monitoring light information.

FIG. 22shows the strain sensing performance of the skin sensor including the strain sensing unit according to an embodiment.FIG. 22is a graph the influence of Schottky contact on bending responsivity, obtained using the skin sensor device1including the active layer347of polycrystalline ZnO.

Referring toFIG. 22, the strain sensing unit340changes in semiconductor properties when skin strain occurs. It is found that as the strain level of the active layer347gradually increases to 0.009%, 0.12%, 0.25%, a conductance change increases. Accordingly, the skin sensor device1including the strain sensing unit340can be sufficiently used as a sensor device for sensing skin strains.

FIG. 23is an image of the skin sensor device attached to the user's skin over time during sweating in the skin according to an embodiment.FIGS. 24A to 24Fshow the monitoring results by the skin sensor device ofFIG. 23.

In the process of monitoring the user's skin condition for a long time, the skin sensor attached to the skin inevitably contacts sweat coming from the user's skin. To maintain long-term accurate monitoring, it is necessary to prevent the skin sensor from delaminating due to sweat and causing damage to the skin.

Referring toFIG. 23, as opposed to the existing skin sensor, the skin sensor device1of the present disclosure has no sweat accumulation at the interface between the skin sensor device1and the skin by high air permeability in the presence of the auxetic hole pattern. It is because air permeability is maintained by the perforated pattern. The skin sensor device1having no sweat accumulation keeps in close contact with the skin.

In contrast, as shown inFIGS. 23 and 24A, the existing skin sensor having no perforated pattern has more sweat accumulation at the interface with the skin. Thus, the existing skin sensor cannot manage sweat accumulation and eventually is separated.

Referring toFIG. 24Bshowing the result of measuring by the image analyzer, quantitative analysis on sweat trapped area confirms that sweat is trapped below the existing skin sensor, while sweat is effectively evacuated from the skin sensor having the perforated pattern.

Additionally, referring toFIG. 24C, the skin sensor device1having the perforated pattern immediately senses the hydration level of the skin, as consistent with the estimated results by a commercial hydration sensor (Corneometer CM 825). In contrast, the existing skin sensor having no perforated pattern has the delayed sensing operation. Based onFIG. 24C, as opposed to the existing skin sensor that allows only vapor exchange, the skin sensor having the perforated pattern allow both vapor and liquid permeation.

For long-term monitoring, it is necessary to consider skin allergic reaction.FIG. 24Dshows the result of monitoring skin allergic reaction by a dermatologist after laminating onto the forearm over a period of 1 week. Referring toFIG. 24D, users wearing the existing nonperforated skin sensor show skin damage, while none of users wearing the skin sensor device1having the perforated pattern show skin irritation. Accordingly, the skin sensor device1has excellent long-term skin compatibility.

Referring toFIG. 24E, after the user sweats, the skin sensor device1having the perforated pattern accurately monitors the hydration and temperature response. In contrast, the existing skin sensor cannot accurately monitor the hydration and temperature response due to malfunction of the skin sensor. As shown inFIG. 24E, in the skin sensor device1of the present disclosure, the measured hydration level/temperature level shows the increased skin hydration and the decreased body temperature by perspiration. That is, the skin sensor device1of the present disclosure measures successful relaxation of the hydration and temperature values after sweating. However, the hydration and temperature values of the existing skin sensor do not obey the current hydration and temperature values of the skin any longer after sweating.

Referring toFIG. 24F, the skin sensor device1having the perforated pattern can accurately measure skin strains since sweat is not trapped. In contrast, the existing skin sensor cannot accurately measure strains due to trapped sweat.

Before sweating, the two sensors accurately monitor tension and relaxation when frowning or relieving. However, after sweating, only the skin sensor of the present disclosure accurately monitors strains without malfunction. In particular, the suspended free-standing structure (for example, the cantilever structure) of the strain sensor reduces the flexural rigidity of the sensing area, thereby suppressing the strain damping effect of the flexible patch60, and thus the skin sensor device1having the perforated pattern has higher strain responsivity (approximately4times).

FIG. 25is an image of a process of monitoring the extent of recovery of the skin to which the skin sensor device is attached.FIG. 26shows the monitoring results ofFIG. 25.

Referring toFIGS. 25 and 26, the skin sensor device1does not impede the recovery of damaged skin when attached to the skin due to high air permeability.

The monitoring results ofFIGS. 25 and 26are obtained by continuously monitoring the skin hydration level for 2 weeks using the skin sensor having the perforated pattern of the present disclosure as a hydration sensor after causing red spots on the skin by applying a Sodium Lauryl Sulfate (SLS) solution.

The result of measuring the moisture level of the control area using Cutometer (Corneometer) without the skin sensor device1is used as control. As a result, it is found that the skin sensor device1maintains long-term sensing accuracy for 2 weeks.

As shown inFIG. 26, the result of measuring the recovery of damaged skin shows three stages: i) keratinization due to dehydration, ii) restoration to normal hydration level and regeneration, iii) recovery of maintaining normal hydration level. The skin area that contacts the skin sensor device1having the perforated pattern shows skin recovery track for 2 weeks in the same way as measured by Cutometer (Corneometer) while the skin is covered with the patch of the skin sensor device1. This signifies i) the perforations prevent the wound healing process from being prohibited by the skin sensor device1attached to the skin due to the full exposure of sweat pores to the external environment, and ii) the skin sensor device1can continuously monitor the skin condition of two persons as a hydration sensor.

FIG. 27is an image of the skin sensor device1attached for a long time according to an embodiment of the present disclosure.FIGS. 28A and 28Bshow the skin monitoring results ofFIG. 27over time.

The skin sensor ofFIGS. 28A and 28Bis attached to the user's wrist for a week. The skin sensor measures the wrist pulse, skin hydration level, skin temperature and light exposure level for a week.

As the skin sensor device1continuously monitors information for a week, it is found that the skin sensor device1does not delaminate from the skin.

Additionally, the skin sensor device1continuously monitors activity information of the skin without malfunction for seven days as shown inFIG. 28A. When the user runs for 30 minutes on the fourth day and the sixth day, increases in the number/intensity of pulse and moisture supply are accurately measured by the strain sensing unit and the hydration sensing unit as shown inFIG. 28B. It is intuitively understood from the graph ofFIG. 28Bthat the heartbeat increases and sweat is produced during activities. Except the running event, the wrist pulse, skin hydration level and skin temperature level are almost uniform. For example, the user's monitoring results include beats per minute (BPM) of 51, skin hydration level of ˜87 keratometry value and skin temperature information of 33.7° C. Additionally, time-space information of an object is distinctly distinguished due to a difference in photoconductivity between an external environment (exposure to the Sun) during the day and home (no light) before sleeping.

Based on the results ofFIG. 28, the skin sensor device1may obtain skin related information including wrist pulse, hydration, temperature and exposure to light using multiple sensing units embedded into the perforated patch. As a result, the skin sensor device1may work as all electronic modules for long-term skin information monitoring.

In the skin sensor device1attached to the skin surface, the sensor module30that performs the sensor operation is disposed on the flexible patch60. As opposed to the commonly used circuit boards, the flexible patch60is soft and sticky. Accordingly, it is difficult to fabricate the skin sensor device1of the present disclosure simply by the process of integrating the circuit components on the substrate in a sequential order.

A method for fabricating the skin sensor device1according to another aspect of the present disclosure may place the sensor module30on the flexible patch60more easily.

FIGS. 29A to 29Oare schematic flowcharts of the method for fabricating a skin sensor device according to another aspect of the present disclosure.FIGS. 29A to 29Oshow the stack status for each process.

Referring toFIGS. 29A to 29I, the method for fabricating a skin sensor device includes: fabricating the sensor module30; and bonding the sensor module30to the flexible patch60.

The step of fabricating the sensor module30includes preparing a parent substrate101(S101) (FIG. 29A). The parent substrate101is made of a rigid material. Additionally, the parent substrate101may be a material having semiconductor properties. For example, the parent substrate may be made of a material including Si, but is not limited thereto. In an embodiment, the first substrate may be high-concentration doped Si (<0.01 Ωcm).

Referring toFIG. 29B, the step of fabricating the sensor module30includes: forming the first sacrificial layer110on the parent substrate101(S110).

The first sacrificial layer110is made of a material capable of separating an upper layer from the parent substrate101through an electrochemical lift-off process. For example, the first sacrificial layer110may be made of a material including at least one of Al, Cu, Fe or a combination thereof.

In an embodiment, the first sacrificial layer110may be a removable material by electrolytic etching. For example, the first sacrificial layer110may be made of a material including Al and/or Ti. The first sacrificial layer110may be an Al/Ti coating layer. Thus, a stack having the Al/Ti coating on the surface of the parent substrate101made of Si is obtained.

When the first sacrificial layer110includes a plurality of materials, each sacrificial material may be coated with different thicknesses. For example, the first sacrificial layer110may include a 200 nm thick Al layer and a 40 nm thick Ti layer.

Referring toFIG. 29C, the step of fabricating the sensor module30includes: forming the first passivation layer200on the first sacrificial layer (S200).

The first passivation layer200is formed by a coating and/or curing process. A variety of spin coating techniques may be used to form the first passivation layer200. The curing process for forming the first passivation layer200may be performed at 200° C. to 300° C., 240° C. to 260° C., for example, approximately 250° C. for 50 minutes to 70 minutes, for example, 1 hour. The thickness may be 2 um, but is not limited thereto.

Referring toFIG. 29D, the step of fabricating the sensor module30includes: forming the electronic circuit unit300(S300). In certain embodiments, the step S300may include: forming the interconnect301(S301). Additionally, the step S300may further include: building the temperature sensing unit310(S310); building the hydration sensing unit320(S320); building the photo sensing unit330(S330); and/or building the strain sensing unit340(S340).

In an embodiment, the step S301of forming the interconnect301includes: depositing a material (for example, Au) for forming the interconnect301on the first passivation layer200; and patterning the deposited interconnect301to form an auxetic hole pattern on the interconnect301at least in part.

The interconnect301may be deposited on a bottom PI200, for example, by e-beam evaporation. The Au interconnect may be 100 nm in thickness.

The auxetic hole pattern may be patterned, for example, by a photoresist based lift-off process using LOR 3A, Microchem.

In an embodiment, the step S310of building the temperature sensing unit310may include: forming the temperature responsive layer317; and patterning the temperature responsive layer317to form the planar mesh structure of the auxetic hole pattern.

The temperature responsive layer317may be formed on the bottom PI layer200, for example, by e-beam evaporation.

The auxetic hole pattern of the temperature responsive layer317may be formed through the lift-off process subsequent to the lift-off of the step S301.

The mesh structure of the auxetic hole pattern is formed as the temperature responsive layer317between the interconnects301by the e-beam evaporation deposition and the subsequent lift-off treatment. Part (for example, the edge) of the temperature responsive layer317and the adjacent interconnect301are connected to each other to complete the auxetic hole pattern. To this end, the same mask may be used in the patterning process.

In an embodiment, the step S320of building the hydration sensing unit320may include: building at least one of the electrode321or the electrode322; forming the hydration responsive layer327on the formed electrode321and/or322; and patterning the hydration responsive layer327to form the planar mesh structure of the auxetic hole pattern.

In an embodiment, the at least one electrode321and at least one electrode322may be built. In this case, the plurality of electrodes321,322may be arranged in an interdigitated array to implement a structure of interdigitated electrodes. The hydration responsive layer327is formed on the plurality of electrodes321,322having the interdigitated electrodes shape. For example, the hydration responsive layer327/the electrode321or322may be implemented as an Au/Cr (100 nm/1 nm) stack.

Referring toFIG. 29E, the step of fabricating the sensor module30includes: forming the second passivation layer400on the electronic circuit unit300(S400).

In an embodiment, some interfaces between the layers200,300,400may undergo chemical treatment to improve the interfacial strength. For example, some interfaces between the layers200,300,400may be treated with 1% v/v 3 APTES (aminopropyltriethoxysilane) in ionized water.

Additionally, referring toFIG. 29F, the step of fabricating the sensor module30includes: patterning the first passivation layer200and the second passivation layer400form the auxetic hole pattern (S500).

The top PI layer400is patterned by plasma treatment. For example, the top PI layer400may be patterned by oxygen plasma treatment using a hard mask made of Cu to form the auxetic hole pattern.

At the same time with the patterning of the top PI layer400, the bottom PI layer200is also patterned.

When the surface of the top PI layer400is exposed to oxygen plasma, the exposed pattern area includes a pattern corresponding to the auxetic hole pattern of the electronic circuit unit300to form a perforated pattern. When the area exposed to oxygen plasma is patterned, an auxetic hole pattern including the pattern corresponding to the auxetic hole pattern of the electronic circuit unit300is formed on the top PI layer400.

When the auxetic hole pattern of the top PI layer400is formed, the bottom PI layer200that directly contacts the top PI layer400in which the electronic circuit unit300is not built is automatically exposed to oxygen plasma. Meanwhile, since the electronic circuit unit300already has an auxetic hole pattern corresponding to the auxetic hole pattern of the top PI layer400at least in part, when the auxetic hole pattern of the top PI layer400is formed in the region in which the electronic circuit unit300is built, the bottom PI layer200is automatically exposed to oxygen plasma through the auxetic hole pattern of the electronic circuit unit300. Thus, the bottom PI layer200has an auxetic hole pattern corresponding to the auxetic hole pattern of the top PI layer400.

As each layer200,300,400of the sensor module30has the auxetic hole pattern at least in part and the shape of each auxetic hole pattern corresponds to each other, when each layer200,300,400is stacked through the steps200to S500, the sensor module30may have an auxetic perforated pattern in which perforations of open channels have a pattern of auxetic properties.

Additionally, in the step of fabricating the sensor module30, each of the steps S200to S400may further include additionally forming an array hole. Additionally, the step of fabricating the sensor module30may further include: installing an alignment key in the array hole formed through patterning. As shown in the upper part ofFIG. 2, the alignment key500of a cross shape is inserted to fix the alignment of the auxetic hole patterns for each layer200,300,400of the sensor module30, thereby maintaining the open channels of the auxetic perforated pattern.

FIGS. 30A to 30Care schematic diagrams of a process of fabricating the sensor module30including the photo sensing unit330according to an embodiment of the present disclosure. The process of fabricating the sensor module30including the photo sensing unit330is similar to the process of fabricating the sensor module30including the other sensing unit (for example,310,320), and difference(s) will be described.

Referring toFIG. 30A, the step S330of building the photo sensing unit330includes: forming the photo responsive layer337connected to the adjacent interconnect301on the first passivation layer200after the step S301of building the adjacent interconnect301. In some embodiments, the step S330of building the photo sensing unit330may further include: forming the capping layer338on the photo responsive layer337.

The adjacent interconnect301to which the photo responsive layer337is connected is formed on the first passivation layer200, and when the adjacent interconnect301is projected toward the flexible patch60, the projection area of the adjacent interconnect301may be disposed near the specific through-hole of the flexible patch60. For example, the adjacent interconnect301may be positioned on two sides such that it is disposed between the specific through-holes of the flexible patch60in the stack structure of the skin sensor device1.

In an embodiment, the photo responsive layer337may be formed such that two ends are positioned on the surface of the adjacent interconnect301. The photo responsive layer337is built with a free-standing structure in the electrode part of the adjacent interconnect301.

Subsequent to the step S330, in the same way as the other units310,320, as shown inFIG. 30B, the second passivation layer400may be formed on the photo sensing unit330(S400).

Referring toFIG. 30C, the step of fabricating the sensor module30may further include: after the steps S330and S400, forming at least one auxiliary through-hole401in the sensing area of the photo sensing unit330in the second passivation layer400(S401). When there is no auxiliary through-hole401, propagation of light or a specific band of light (for example, UV) to the photo responsive layer337may be blocked by the top PI layer400, and thus light-induced electric current may not be generated. Additionally, the photo sensing unit330may be positioned on the flexible patch60in the opposite direction to the strain design to reduce strain dependency of the device conductance.

The second passivation layer400includes the auxiliary through-hole401formed by patterning the sensing area of the photo sensing unit330and the auxetic hole pattern formed by patterning part or all of the remaining area. Here, the remaining area is an area except the specific through-hole in which the photo sensing unit330is built.

Referring back toFIG. 29D, the step S340of building the strain sensing unit340includes: forming the active layer347connected to the adjacent interconnect301on the first passivation layer200after the step S301of building the adjacent interconnect301.

The adjacent interconnect301to which the active layer347is connected is formed on the first passivation layer200, and when the adjacent interconnect301is projected toward the flexible patch60, the projection area of the adjacent interconnect301may be disposed near the specific through-hole of the flexible patch60. For example, the adjacent interconnect301may be positioned on two sides such that it is disposed between the specific through-holes of the flexible patch60in the stack structure of the skin sensor device1.

In an embodiment, the active layer347may be formed such that two ends are positioned on the surface of the adjacent interconnect301. The active layer347is built with a free-standing structure in the electrode part of the adjacent interconnect301. The active layer347may be formed with the planar structure ofFIG. 17by deposition by radio frequency deposition and patterning. The active layer347may be made of polycrystalline ZnO. Thus, the deposition process for the ZnO thin film layer347may be performed at 150° C.-250° C., 180° C.-220° C., 200° C. The body of the active layer347is patterned using a chemical solution such as HCL solution.

In some embodiments, the step S340of building the strain sensing unit340may further include: forming the bottom capping layer346that will be positioned at the interface between the active layer347and the first passivation layer200; and/or forming the top capping layer348that will be positioned at the interface between the active layer347and the second passivation layer400.

To make use of the piezoelectric effect of the strain sensing unit340having the ZnO layer, Schottky barrier may be formed by inserting a HfO2layer as the bottom capping layer346into ZnO/Au contact at 200-250° C., for example, approximately 225° C. by an atomic layer deposition process.

After the stack of the parent substrate101, the first sacrificial layer110and the sensor module30is formed, the step of fabricating the skin sensor device1includes: bonding the sensor module30to the flexible patch60.

Referring toFIG. 29G, the step of bonding the sensor module30to the flexible patch60includes: forming the second sacrificial layer610on one surface of the sensor module30(for example, one surface of the second passivation layer400).

The second sacrificial layer610is made of a material that is different from the first sacrificial layer110. The second sacrificial layer610is made of a material that is not removed in the process for removing the first sacrificial layer110(for example, an electrochemical lift-off process). The material of the second sacrificial layer610may be a material that is not affected by heat or decomposition. For example, the second sacrificial layer610may be made of a water-insoluble polymer (for example, PMMA, etc.), or any other water-insoluble material.

Referring toFIG. 29H, the step of bonding the sensor module30to the flexible patch60includes: attaching a transferor630to the second sacrificial layer610(S630). The transferor630may be a thermal release tape (TRT), but is not limited thereto. The transferor630may be transparent, but is not limited thereto.

Referring toFIG. 29I, the step of bonding the sensor module30to the flexible patch60includes: removing the first sacrificial layer110to separate the parent substrate101from the sensor module30(S650). The first sacrificial layer110may be removed by an electrochemical lift-off process. The first sacrificial layer110is electrolyzed in a salty solvent.

In an embodiment, to promote the decomposition of the first sacrificial layer110, the solvent containing the stack of the step S101to S630may be heated (S650).

Additionally, the step of bonding the sensor module30to the flexible patch60includes: bonding the sensor module30separated from the parent substrate101to the flexible patch60(S670). The sensor module30is bonded to the flexible patch60by transferring part of the sensor module30(i.e., the first passivation layer200) opposite the transferor630to the surface of the flexible patch60using the transferor630.

In an embodiment, the sensor module30is bonded such that the auxetic hole pattern of the flexible patch60and the auxetic hole pattern of the sensor module30correspond to each other (S670). After the bonding, when the through-hole of the auxetic hole pattern of the flexible patch60and the through-hole of the auxetic hole pattern of the sensor module30are aligned to correspond to each other, a perforated pattern extending outward from the skin surface is formed in the skin sensor device1.

In an embodiment, the flexible patch60may have an array hole corresponding to the array hole of the sensor module30. These array holes may have a planar shape that matches the alignment key500. After the bonding, the connection of the flexible patch60and the sensor module30may be fixed by the alignment key500.

In alternative embodiments, the step of bonding the sensor module30to the flexible patch60may further include: before the step S670, fabricating the flexible patch60having the auxetic hole pattern using a mold substrate.

Referring toFIG. 29J, the step of fabricating the flexible patch60may include: coating a flexible material on the mold substrate661having a furrow pattern for forming the auxetic hole pattern to form the flexible patch60(S663).

An island step that protrudes from the surface of the mold substrate661in the furrow pattern of the mold substrate661matches the through-hole in the auxetic hole pattern of the flexible patch60. As shown inFIG. 29J, each island step has a dumbbell plane or a circular plane that matches the through-hole that forms the auxetic hole pattern. A planar array of the island step of the mold substrate661matches the planar structure of the auxetic hole pattern formed by the dumbbell holes/circular hole that the flexible patch60will have.

In contrast, the furrow surrounded by the island step in the furrow pattern of the mold substrate661matches the planar shape of the sidewall that surrounds the through-hole in the auxetic hole pattern of the flexible patch60.

The flexible material of which the flexible patch60is made is coated on the furrow of the mold substrate661and the internal space of the furrow is filled with the flexible material. As shown inFIG. 29J, the height of the filled flexible layer may be higher than the furrow height of the mold substrate661.

In an embodiment, the flexible material may be coated to form the first flexible layer61and the second flexible layer62(S663).

Referring toFIG. 29K, the step of fabricating the flexible patch60may include: removing part or all of the flexible patch60present on top of the sidewall (i.e., the island step) that form the furrow (S665).

The flexible patch60beyond the furrow (i.e., formed at a higher position than the sidewall of the furrow of the mold substrate661) is removed at least in part to expose part or all of the sidewall surface on top of the sidewall through the flexible patch60(S665).

In an embodiment, all or part of the flexible patch60present on top in an uncured state may be removed.

The part beyond the furrow is removed by contacting a board (not shown) with the flexible patch layer beyond the sidewall of the furrow of the mold and rubbing the board (not shown) and/or the flexible patch60(a cast-mold structure) (S665). The board plays a role of a plastering board that pushes the excessive flexible material to remove it.

Referring toFIG. 29L, the step of bonding the sensor module30to the flexible patch60may include: after the step S665, arranging the sensor module30adhered with the transferor630on the surface of the flexible patch60formed on the mold substrate661such that the through-hole of the auxetic hole pattern of the flexible patch60and the through-hole of the auxetic hole pattern of the sensor module30correspond to each other (S667). For example, the sensor module30and the flexible patch60may be bonded such that each island step of the mold substrate661corresponds to each through-hole of the sensor module30.

FIGS. 31A to 31Dare plan views of the sensor module transferred after attached to the TRT630.FIGS. 31B to 31Dare partial enlarged views ofFIG. 31A.

As shown inFIG. 31, the sensor module30of the structure of the sensor module30; the flexible patch60; and the second sacrificial layer610and the transferor630are bonded to the surface of the flexible patch60ofFIG. 29Kthrough the transferor630(S667).

The sidewall part of the furrow of the mold substrate661that matches the through-hole of the flexible patch60is arranged to correspond to the through-hole of the sensor module30(S667).

In an embodiment, the step S667of arranging may include compressing the arranged sensor module30with the flexible patch60.

Referring toFIG. 29M, the step of bonding the sensor module30to the flexible patch60may include: separating the flexible patch60bonded with the sensor module30from the mold substrate661(S669). The structure of the sensor module30; the flexible patch60; the second sacrificial layer610and the transferor630is separated from the mold substrate661through the transferor630.

Referring toFIG. 29N, the step S670of bonding the sensor module30separated from the parent substrate101to the flexible patch60may include separating the transferor630from the structure of the sensor module30; the flexible patch60; the second sacrificial layer610and the transferor630; and removing the second sacrificial layer610.

For example, when the transferor630is a TRT, the TRT630may be separated by heating the structure at approximately 150° C.

The second sacrificial layer610may be removed by chemical etching. The second sacrificial layer610is a water-insoluble material. The remaining structure including the second sacrificial layer610may be dipped into an etching solution (for example, acetone) to remove the second sacrificial layer610(for example, PMMA). When the PMMA layer610dissolves, the skin-attachable skin sensor device1having a perforated pattern is fabricated.

In an embodiment, the step S670may further include: cleaning off the etching solution residue or the surface residue from the structure of the skin sensor device1free of the second sacrificial layer.

For example, acetone remaining on the surface of the sensor module30(for example, the second passivation layer400) from which the second sacrificial layer610is peeled using cellulose wipers (TX2009, Texwipe) may be cleaned off with isopropanol.

The separated parent substrate101may be reused to fabricate other sensor module30.

Referring toFIG. 29O, the parent substrate101separated in the step S650may be used to fabricate other sensor module30. There is no need to prepare a separate parent substrate101to fabricate other sensor module30. As a result, it is possible to minimize economic ad physical resources for fabricating the skin sensor device1.

While the present disclosure has been hereinabove described with reference to the embodiments shown in the drawings, this is provided by way of illustration and those skilled in the art will understand that a variety of modifications and variations may be made thereto. However, it should be noted that such modifications fall in the technical protection scope of the present disclosure. Accordingly, the true technical protection scope of the present disclosure should be defined by the technical spirit of the appended claims.

DETAILED DESCRIPTION OF MAIN ELEMENTS

30: Electronic module

60: Flexible patch

110: First sacrificial layer

300: Electronic circuit unit

310: Temperature sensing unit

320: Hydration sensing unit

330: Photo sensing unit

340: Strain sensing unit