Patent Publication Number: US-2022231069-A1

Title: Image-sensing device

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This Application claims priority of Taiwan Patent Application No. 110102272, filed on Jan. 21, 2021. the entirety of which is incorporated by reference herein. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates to an image-sensing device, and more particularly to an image-sensing device with nanowells. 
     Description of the Related Art 
     An image sensor is a semiconductor device that converts light images into electrical signals. Image sensors can generally be classified as either charge-coupled devices (CCD) or complementary metal-oxide-semiconductor (CMOS) image sensors, Among these image sensors, complementary metal-oxide-semiconductor image sensor includes a photodiode for detecting incident light and converting it into an electrical signal, and a logic circuit for transmitting and processing the electrical signal. 
     In addition to the general purpose of simply sensing images, more and more image sensors have been applied to various inspection tasks, such as biomedical inspections. Specifically, various characteristics of the object to be tested can be detected or determined by the light excited by the object to be tested after being irradiated by an external light source. 
     However, when the size of the sensing cell or pixel of the image sensor is reduced, there will be, for example, cross-talk, photon response non-uniformity (PRNU), low signal-to-noise ratio (SNR), and other issues. Therefore, an image-sensing device that can improve performance is desired. 
     BRIEF SUMMARY OF THE INVENTION 
     Image-sensing devices are provided. An embodiment of an image-sensing device is provided. The image-sensing device includes a substrate, a first dielectric layer, an image sensor array, a plurality of nanowells and a plurality of electrodes. The first dielectric layer is formed on the substrate, and has a first side and a second side opposite to the first side. The image sensor array is formed between the substrate and the second side of the first dielectric layer, and includes a plurality of image-sensing cells. The nanowells are formed in the first dielectric layer, and each of the nanowells has an opening on the first side of the first dielectric layer. Each of the electrodes extends from the second side to the first side of the first dielectric layer and is located between two adjacent nanowells. 
     Moreover, an embodiment of an image-sensing device is provided. The image-sensing device includes a substrate, an image sensor array, a first dielectric layer, a first passivation layer, a second dielectric layer, a plurality of nanowells and a plurality of electrodes. The image sensor array is -formed on the substrate, and comprising a plurality of image-sensing cells. The first dielectric layer is formed on the image sensor array. The first passivation layer is formed on the first dielectric layer. The second dielectric layer is formed on the first passivation layer. The nanowells are formed in the second dielectric layer, and each of the nanowells has an opening on the upper surface of the second dielectric layer. Each of the electrodes extends from the first dielectric layer through the first passivation layer to the second dielectric layer and is disposed between two adjacent nanowells. 
     A detailed description is given in the following embodiments with reference to the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein: 
         FIG. 1  shows a cross-sectional view of an image-sensing device according to some embodiments of the invention. 
         FIG. 2A  shows a rolling shutter image-sensing cell according to some embodiments of the invention. 
         FIG. 2B  shows a global shutter image-sensing cell according to some embodiments of the invention. 
         FIG. 3  shows a top view of the dipoles of the object to be tested (e.g., the object to be tested of  FIG. 1 ) in the nanowell array when the electrode of the image-sensing device in  FIG. 1  is operated in an unbiased mode according to some embodiments of the invention. 
         FIG. 4  shows a top view of dipoles of the object to be tested (e.g., the object to be tested in  FIG. 1 ) in the nanowell array when the electrodes of the image-sensing device in  FIG. 1  are operated in a first bias mode according to some embodiments of the invention. 
         FIG. 5  shows a top view of dipoles of the object to be tested (e.g., the object to be tested in  FIG. 1 ) in the nanowell array when the electrodes of the image-sensing device in  FIG. 1  are operated in a second bias mode according to some embodiments of the invention. 
         FIGS. 6A through 6D  show the top views of dynamically assigning electrodes around the nanowells in a third bias mode according to some embodiments of the invention. 
         FIGS. 7A through 7D  show the top views of dynamically assigning electrodes around the nanowell in a fourth bias mode according to some embodiments of the invention. 
         FIG. 8  shows a cross-sectional view of the nano-well and the surrounding electrodes according to some embodiments of the invention. 
         FIGS. 9A through 9F  show cross-sectional views illustrating a semiconductor structure forming the image-sensing device according to some embodiments of the invention. 
         FIG. 10  shows a cross-sectional view of a semiconductor structure forming the image-sensing device according to some embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best-contemplated mode of carrying out the invention. This description is made for the purpose of illustrating the general principles of the invention and should not be taken in a limiting sense. The scope of the invention is best determined by reference to the appended claims. 
     It should be understood that, the elements or devices of the drawings may exist in various forms well known to those skilled in the art. In addition, relative terms such as “lower” or “bottom” and “higher” or “top” may be used in the embodiments to describe the relative relationship between one element of the figure and another element. It can be understood that if the illustrated device is turned upside down and turned upside down, the element described on the “lower” side will become the element on the “higher” side. The embodiments of the disclosure can be understood together with the drawings, and the drawings of the disclosure are also considered as a part of the disclosure description. It should be understood that the drawings disclosed in this disclosure are not drawn to scale. In fact, the dimensions of the elements may be arbitrarily enlarged or reduced in order to clearly show the features of the present invention. 
     Furthermore, the elements or devices of the drawings may exist in various forms well known to those skilled in the art. Moreover, understandably, although the terms “first”, “second”, “third”, etc. may be used herein to describe various elements or parts, these elements, components, or parts should not be limited by these terms, and these terms are only Is used to distinguish different elements, components, areas, layers or parts. Therefore, a first element, component, area, layer or part discussed below may be referred to as a second element, component, area, layer or part without departing from the teachings of this disclosure. 
     In some embodiments of the present disclosure, terms such as “connect” and “interconnect” with regard to bonding and connection may refer to the two structures being in direct contact, or may refer to the two structures not being in direct contact unless specifically defined. There are other structures between these two structures. In addition, the term “joining and connecting” may also include a case where both structures are movable or both structures are fixed. 
     It should he understood that when an element or layer is referred to as being “on” or “connected” with another element or layer, it can be directly on or directly connected to another element or layer. The layers are connected, or there may also be intervening elements or layers. Conversely, when an element is referred to as being “directly” on or on another element or “directly” connected to another element or layer, there are no intervening elements. 
     Unless otherwise defined, all terms (including technical and scientific terms; used herein have the same meaning as commonly understood by those skilled in the art to which this disclosure belongs. It is understandable that these terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning consistent with the background or context of the related technology and this disclosure. It should not be interpreted in an idealized or excessively formal manner unless specifically defined in the disclosed embodiments. 
       FIG. 1  shows a cross-sectional view of an image-sensing device  100  according to some embodiments of the invention. It should be understood that, according to some embodiments, additional features may be added to the image-sensing device  100  described below. According to some embodiments, some features described below may be replaced or deleted. 
     As shown in  FIG. 1 , the image-sensing device  100  includes a substrate  102 . In some embodiments, the substrate  102  is a semiconductor substrate. For example, the material of the substrate  102  may include monocrystalline, polycrystalline, or amorphous silicon (Si) or germanium (Ge) or a combination thereof. In some embodiments; the substrate  102  is formed of a compound semiconductor. For example, in some embodiments, the material of the substrate  100  may include silicon carbide (SiC), gallium arsenide (GaAs), gallium phosphide (GaP), indium phosphide (InP), indium arsenide (InAs), or a combination thereof. In addition, according to some embodiments, the material of the substrate  102  may be formed of alloy semiconductors. For example, in some embodiments, the material of the substrate  102  may include germanium silicide (SiGe), aluminum gallium arsenide (AlGaAs), gallium indium arsenide (GaInAs), gallium indium phosphide (GaInP), gallium arsenide (GaAsP)) or a combination thereof. 
     In  FIG. 1 , the image-sensing device  100  further includes an image sensor array  110  formed on the substrate  102 . In some embodiments, some components (or elements) of the image sensor array  110  is disposed in the substrate  102 . The image sensor array  110  includes a plurality of image-sensing cells  104  arranged in multiple rows and multiple columns, and each image-sensing cell  104  includes a photodiode. The photodiode is configured to receive light and convert it into electrical signals. In some embodiments, the image-sensing cell  104  may be a rolling shutter image-sensing cell or a global shutter image-sensing cell. 
     Referring to  FIGS. 2A and 2B ,  FIG. 2A  shows a rolling shutter image-sensing cell  104 A according to some embodiments of the invention, and  FIG. 2B  shows a global shutter image-sensing cell  104 B according to some embodiments of the invention. In the image-sensing cells  104 A and  104 B, the photodiode PD may include the source and drain of a metal oxide semiconductor (MOS) transistor, and the source and drain of the MOS transistor are configured to transmit current to other components, such as other MOS transistors. In some embodiments, the image-sensing cells  104 A and  104 B may include a transmission gate TX, a reset gate RST, a floating diffusion FD, a source follower SF, or a combination thereof. Furthermore, the image-sensing cells  104 A and  104 B are further coupled to external devices or circuits, so as to transmit the output signal PixOut to other circuits, such as a signal processor (not shown). It is noted that  FIGS. 2A and 2B  only simply show some components of the image-sensing cells  104 A and  104 B, and are not intended to limit the invention. Any image-sensing cell suitable for rolling shutters or global shutters can be used as the image-sensing cell of the invention. 
     Referring back to  FIG. 1 , the image-sensing device  10  further includes a dielectric layer  115 , and the dielectric layer  115  is formed on the image sensor array  110 . In other words, the dielectric layer  115  is configured to cover the image-sensing cells  104  of the image sensor array  110 . In some embodiments, the material of the dielectric layer  115  may include silicon oxide, silicon nitride, silicon oxynitride, high-k dielectric materials, other suitable dielectric materials, or the foregoing combination. In some embodiments, the high dielectric constant dielectric material may include metal oxide, metal nitride, metal silicide, metal aluminate, zirconium silicate, zirconium aluminate, or a combination thereof. 
     In some embodiments, the dielectric layer  115  is formed by the physical vapor deposition (PVD), chemical vapor deposition (CVD), coating process, other suitable method, or a combination thereof. The physical vapor deposition process may include, for example, a sputtering process, an evaporation process, or pulsed laser deposition. The chemical vapor deposition process may include, for example, a low pressure chemical vapor deposition process (LPCVD), a low temperature chemical vapor deposition process (LLCM), a rapid temperature rise chemical vapor deposition process (RTCVD), a plasma assisted chemical vapor deposition process (PECVD), or atomic layer deposition process (ALD) and so on. 
     In  FIG. 1 , the image-sensing device  100  further includes an interconnect structure  120 , and the interconnect structure  120  is formed in the dielectric layer  115 . In some embodiments, the projection (not shown) of the interconnect structure  120  on the substrate  102  is overlapped between two adjacent image-sensing cells  104 , that is, the edge of the image-sensing cells  104 . In some embodiments, the interconnect structure  120  includes a plurality of conductive layers  122 ,  124 , and  126 . Each of the conductive layers  122 ,  124 , and  126  includes a plurality of conductive electrodes, so as to transmit signals in the image-sensing cells  104  of the image-sensing device  100  and related circuits. In  FIG. 1 , the conductive layer  122  is the lowest conductive layer adjacent to the image sensor array  110 , and the conductive layer  126  is the highest conductive layer away from the image sensor array  110 . In addition, the conductive layer  124  is an intermediate conductive layer disposed between the conductive layers  122  and  126 . It should be understood that although three layers of conductive layers  122 ,  124 , and  126  are exemplarily illustrated, the invention is not limited thereto. In accordance with different embodiments, according to need, suitable amount and structure of the conductive layer may be arranged to form the interconnect structure  120 . 
     In some embodiments, the interconnect structure  120  may include a metallic conductive material, a transparent conductive material, or a combination thereof. The metallic conductive material may include copper (Cu), aluminum (Al), gold (Au), silver (Au), titanium (Ti), tungsten (W), molybdenum (Mo), nickel (Ni), copper alloy, aluminum alloy, gold alloy, silver alloy, titanium alloy, tungsten alloy, molybdenum alloy, nickel alloy, or a combination thereof. The transparent conductive material may include a transparent conductive oxide (TCO). For example, the transparent conductive oxide may include indium tin oxide (ITT), tin oxide (SnO), zinc oxide (ZnO), indium zinc oxide (IZO), indium gallium zinc oxide (IGZO), indium tin zinc oxide (ITZO), antimony tin oxide (ATO), antimony zinc oxide (AZO), or a combination thereof. 
     In some embodiments, a physical vapor deposition (PVD) process, a chemical vapor deposition (CVD) process, a coating process, other suitable processes, or a combination thereof may be used to form the interconnect structure  120 . In some embodiments, a patterning process may be used to form the interconnect structure  120 . In some embodiments, the patterning process may include a photolithography process and an etching process. The photolithography process may include, but is not limited to, photoresist coating (for example, spin coating), soft baking, hard baking, mask alignment, exposure, post-exposure baking, photoresist development, cleaning, and drying. The etching process may include a. dry etching process or a wet etching process, but it is not limited thereto. 
     In  FIG. 1 , the image-sensing device  100  further includes a passivation layer  125 , and the passivation layer  125  is formed over the dielectric layer  115 . In some embodiments, the passivation. layer  125  may include silicon nitride (Si 3 N 4 ), silicon oxide (SiO 2 ), silicon oxynitride (SiON), aluminum oxide (Al 2 O 3 ), aluminum nitride (AlN), polyimide (PI), benzocyclobutene (BCB), polybenzoxazole (PBO), other dielectric materials, or a combination thereof. In some embodiments, metal organic vapor deposition methods, chemical vapor deposition methods (such as low pressure chemical vapor deposition or plasma assisted chemical vapor deposition), spin coating methods, other appropriate methods, or combinations thereof can be used to form the passivation layer  125  on the dielectric layer  115 . The passivation layer  125  can protect the underlying structure, serve as a buffer between the structure to be formed later, and provide physical isolation and structural support. 
     In  FIG. 1 , the image-sensing device  100  further includes a dielectric layer  135 , and the dielectric layer  135  is formed on the passivation layer  125 . The dielectric layer  135  has a first side  135 A and a second side  135 B, and the first side  135 A is opposite to the second side  135 B. In some embodiments, the first side  135 A of the dielectric layer  135  is the upper surface, and the second side  135 B of the dielectric layer  135  is the lower surface. The second side  135 B of the dielectric layer  135  is in contact with the passivation layer  125 . In some embodiments, the material of the dielectric layer  135  may include silicon oxide, silicon nitride, silicon oxynitride, high-k dielectric materials, other suitable dielectric materials, or combinations thereof. In some embodiments, the high-k dielectric material may include metal oxides, metal nitrides, metal silicides, metal aluminates, zirconium silicates, zirconium aluminates, or combinations thereof. 
     In  FIG. 1 , the image-sensing device  100  further includes a plurality of nanowells  150 . Each nanowell  150  has an opening  155  on the first side  335 A of the dielectric layer  135 . Furthermore, there is a depth (or thickness) D 1  between the bottom surface  157  of the nanowell  150  and the opening  155 , and the dielectric layer  135  has a depth D 2  greater than the depth D 1 , that is, D 2 &gt;D 1 . In some embodiments, the width (or diameter) W 1  of the opening  155  is equal to the width W 2  of the bottom surface  157 , that is, W 1 =W 2 . In some embodiments, the width W of the opening  155  is greater than the width W 2  of the bottom surface  157 , that is, W 1 &gt;W 2 . Moreover, the nanowells  150  are separated by the first portion  135 C of the dielectric layer  135 . 
     When the object to be tested  200  is filled into the nanowells  150 , it can be excited by the excitation light from the upper light source (not shown). After the object to be tested  200  is excited, the object to be tested  200  emits light in a specific wavelength range, and the emitted light can be detected by the image-sensing cells  104  to determine the characteristics of the object to be tested  200 . In some embodiments, the object to be tested  200  may be included in the sample solution (or chemical liquid)  210  filled in the nanowells  150 . 
     In different embodiments, according to the characteristics of the tag of the object to be tested  200 , excitation light with a suitable wavelength or frequency range is provided. For example, the tag can be excited to generate fluorescence or luminescence, but the present invention is not limited thereto. In some embodiments, the light source (not shown) may include polarized light, unpolarized light, or a combination thereof. 
     In some embodiments, the object to be tested  200  may include a biological molecule, a chemical molecule, or a combination thereof. For example, in some embodiments, the object to be tested  200  may include deoxyribonucleic acid (DNA), ribonucleic acid (RNA), proteins, cells, other organic and inorganic small molecules, or a combination thereof, but the present disclosure is not limited thereto. Moreover, in some embodiments, the object to be tested  200  may include a fluorescent marker. 
     In  FIG. 1 , the image-sensing device  100  further includes a plurality of electrodes  140 . In some embodiments, the electrode  140  may be a via or a contact. In addition, each electrode  140  is in contact with and formed on the conductive layer  126  of the interconnect structure  120 , and extends to the first side  135 A of the dielectric layer  135  through the dielectric layer  115 , the passivation layer  125 , and the dielectric layer  135  in sequence until reaching the first part  135 C of the dielectric layer  135 . In other words, each electrode  140  is disposed between two adjacent nanowells  150 . In addition, the depth D 3  of the electrode  140  is greater than the depth D 2  of the dielectric layer  135 , that is, D 3 &gt;D 2 . 
     In the image-sensing device  100 , the image-sensing cell  104  can detect the light emitted by the object to be tested  200 . By controlling the voltage (or bias and polarity) of the electrode  140 , an electric field is generated in the nanowell  150  to control the direction of the dipoles of the object to be tested  200 , so as to reduce the influence of cross-talk. Furthermore, by periodically adjusting the voltage of the electrode  140 , the dipole moment and/or the moment of inertia of the object to be tested  200  are obtained. Therefore, in addition to the light emitted by the object to be tested  200 , the image-sensing device  100  can also determine the characteristics of the object to be tested  200  according to the dipole moment and/or the moment of inertia of the object to he tested  200 , so as to identify the object to be tested  200 . 
       FIG. 3  shows a top view of the dipoles  205  of the object to be tested (e.g., the object to be tested  200  of  FIG. 1 ) in the nanowell array  300 A when the electrode  140  of the image-sensing device  100  in  FIG. 1  is operated in an unbiased mode according to some embodiments of the invention. In  FIG. 3 , since no bias is applied to the electrodes  140 , the electrodes  140  are not shown. In addition, it should be noted that the nanowell array  300 A in  FIG. 3  shows a 4×4 array of nanowells  150 . In other embodiments, the nanowell array  300 A may include a greater or lesser number of nanowells  150 . The dipole  205  is a structure formed by two positively and negatively charged particles with a short distance. As shown in  FIG. 3 , when the electrodes  140  are operated in the unbiased mode, the dipole  205  in each nanowell  150  is randomly arranged. Therefore, the sum of the dipoles  205  in the nanowell array  300 A is randomly polarized, which is prone to crosstalk and causes high photon response non-uniformity (PRNU). Moreover, when the electrodes  140  are operated in the unbiased mode, the direction of the dipole  205  in the nanowell  150  is also unpredictable. 
     In the image-sensing device  100 , the shape of the nanowell  150  is a regular octagon. In some embodiments, the shape of the nanowell  150  is an equilateral polygon. In some embodiments, the shape of the nanowell  150  is an equilateral polygon with more than three sides. In some embodiments, the shape of the nanowell  150  is circular. 
       FIG. 4  shows a top view of dipoles  205  of the object to be tested (e.g., the object to be tested  200  in  FIG. 1 ) in the nanowell array  300 B when the electrodes  140  of the image-sensing device  100  in  FIG. 1  are operated in a first bias mode according to some embodiments of the invention. It is worth noting that the nanowell array  300 B in  FIG. 4  shows the nanowell  150  of the 4×4 array. in other embodiments, the nanowell array  300 B may include a greater or lesser number of nanowells  150 . As shown in  FIG. 4 , the electrode  140 A represents the electrode  140  with a high voltage, and the electrode  140 B represents the electrode  140  with a low-voltage. In some embodiments, the electrode  140 A has a positive voltage (e.g., +3V), and the electrode  140 B has a negative voltage (e.g., −3V). In some embodiments, the electrode  140 A has a voltage (e.g., 5V) greater than the ground voltage, and the electrode  140 B has a ground voltage (e.g., 0V). In some embodiments, the voltages of the electrode  140 A and the electrode  140 B can be changed or interchanged over time. For example, at a first time point, the electrode  140 A has a positive voltage and the electrode  140 B has a negative voltage. Next, at the second time point, the electrode  140 A has a negative voltage and the electrode  140 B has a positive voltage. 
     In the nanowell array  300 B, each nanowell  150  is surrounded by an electrode  140 A and an electrode  140 B, and the voltage of the electrode  140 A is greater than the voltage of the electrode  140 B. Therefore, in each nanowell  150 , when the applied electric field (as indicated by the arrow) is large enough, the direction of the dipole  205  of the object to be tested (such as the object to be tested  200  in  FIG. 1 ) is from the electrode  140 A with a high voltage to the electrode  140 B with a low voltage. For example, for the nanowell  150   a   1 , the nanowell  150   a   1  is surrounded by the electrode  140 A_ 1  and the electrode  140 B_ 1 , and the electrode  140 A_ 1  is arranged at the lower right of the nanowell  150   a   1  and the electrode  140 B_ 1  is arranged at the upper left of the nanowell  150   a   1 . Therefore, the direction of the dipole  205  in the nanowell  150   a   1  is from the electrode  140 A_ 1  to the electrode  140 B_ 1  (i.e., from lower right to upper left). Similarly, the nanowell  150   a   2  is surrounded by the electrodes  140 A_ 1  and  140 B_ 2 , and the electrode  140 A_ 1  is arranged at the lower left of the nanowell  150   a   2  and the electrode  140 B_ 2  is arranged at the upper right of the nanowell  150   a   2 . Therefore, the direction of the dipole  205  in the nanowell  150   a   2  is from the electrode  140 A_ 1  to the electrode  140 B_ 2  (i.e., from lower left to upper right). In addition, the nanowell  150   b   1  is surrounded by the electrodes  140 A_ 1  and  140 B_ 3 , and the electrode  140 A_ 1  is arranged at the upper right of the nanowell  150   b   1  and the electrode  140 B_ 3  is arranged at the lower left of the nanowell  150   b   1 . Therefore, the direction of the dipole  205  in the nanowell  150   b   1  is from the electrode  140 A_ 1  to the electrode  140 B_ 3  (i.e. from the upper right to the lower left). Furthermore, the nanowell  150   b   2  is surrounded by the electrodes  140 A_ 1  and  140 B_ 4 , and the electrode  140 A_ 1  is arranged at the upper left of the nanowell  150   b   2  and the electrode  140 B_ 4  is arranged al the lower right of the nanowell  150   b   2 . Therefore, the direction of the dipole  205  in the nanowell  150   b   2  is from the electrode  140 A_ 1  to the electrode  140 B_ 4  (i.e. from the upper left to the lower right). 
     In the nanowell array  300 B each electrode  140  disposed inside the array is surrounded by four nanowells. For example, the electrode  140 A_ 1  is surrounded by four nanowells  150   a   1 ,  150   a   2 ,  150   b   1 , and  150   b   2  that is, the electrode  140 A_ 1  is arranged between the nanowells  150   a   1 ,  150   a   2 ,  150   b   1  and  150   b   2 . Similarly, the electrode  140 B_ 4  is surrounded by four nanowells  150   b   2 ,  150   b   3 ,  150   c   2 , and  150   c   3 , that is, the electrode  140 B_ 4  is arranged between the nanowells  150   b   2 ,  150   b   3 ,  150   c   2 , and  150   c   3 . 
     In the first bias mode, the electrodes  140 B are arranged (or assigned) in odd rows of the electrode array, and the electrodes  140 A are arranged (or assigned) in even rows of the electrode array. For example, the electrodes  140 B_ 1  and  140 B_ 2  are arranged in the first row of the electrode array, and the electrode  140 A_ 1  is arranged in the second row of the electrode array. In addition, the electrodes  140 B are arranged (or assigned) in odd columns of the electrode array, and the electrodes  140 A are arranged (or assigned) in even columns of the electrode array. For example, the electrodes  140 B_ 1  and  140 B_ 2  are respectively arranged in the first column and the third column of the electrode array, and the electrode  140 A_ 1  is arranged in the second column of the electrode array. In other words, the electrodes  140 A and  140 B are assigned on staggered lines (e.g., staggered columns and rows). By assigning the electrodes  140 A and  140 B and controlling the voltages of the electrodes  140 A and  140 B, the sum of the dipoles  205  in the nano-well array  300 B is controllable, so the optical response signal distribution is controllable, and the crosstalk phenomenon can also be reduced. 
       FIG. 5  shows a top view of dipoles  205  of the object to he tested (e.g., the object to be tested  200  in  FIG. 1 ) in the nanowell array  300 C when the electrodes  140  of the image-sensing device  100  in  FIG. 1  are operated in a second bias mode according to some embodiments of the invention. It should be noted that the nanowell array  300 C in  FIG. 5  shows the nanowell  150  of the 4×4 array. In other embodiments, the nanowell array  300 C may include a greater or lesser number of nanowells  150 . The nanowell array  300 C in  FIG. 5  and the nanowell array  300 B in  FIG. 4  have similar configurations of electrodes  140 A and  140 B. The difference between the nanowell array  300 C in  FIG. 5  and the nanowell array  300 B in  FIG. 4  is that the nanowell array  300 C further includes the electrodes  140 C. In  FIG. 5 , the electrode  140 A represents the electrode  140  having a high voltage, the electrode  140 B represents the electrode  140  having a low voltage, and the electrode  140 C represents the electrode  140  having an average voltage (or intermediate voltage). In some embodiments, the electrode  140 A has a positive voltage (e.g., +3V), the electrode  140 B has a negative voltage (e.g., −3V), and the electrode  140 C has a ground voltage (e.g., 0V). In some embodiments, the electrode  140 A has a higher voltage (e.g., 5V) the electrode  140 B has a ground voltage (e.g., 0V), and the electrode  140 C has an intermediate voltage (e.g., 2.5V, 3V, etc.). 
     In the nanowell array  300 C, each nanowell  150  is surrounded by one electrode  140 A, one electrode  140 B, and two electrodes  140 C. In addition, the voltage of the electrode  140 A is greater than the voltage of the electrode  140 C, and the voltage of the electrode  140 C is greater than the voltage of the electrode  140 B. Therefore, in each nanowell  150 , the direction of the dipoles  205  of the object to be tested (not shown) is from the electrode  140 A with a high voltage to the electrode  140 B with a low voltage. 
     In  FIG. 5 , the nanowell  150   a   1  is surrounded by the electrode  140 A_ 1 , the electrode  140 B_ 1  and the electrodes  140 C_ 1  and  140 C_ 2 . The electrode  140 A_ 1  is arranged on the lower right of the nanowell  150   a   1 , the electrode  140 C_ 1  is arranged on the upper right of the nanowell  150   a   1 , the electrode  140 B_ 1  is arranged on the upper left of the nanowell  150   a   1 , and the electrode  140 C_ 2 . is arranged on the lower left of the nanowell  150   a   1 . When the applied electric field (as indicated by the arrow) is large enough, the direction of the dipoles  205  of the object to be tested (such as the object to be tested  200  in  FIG. 1 ) is from the electrode with a high voltage to the electrode with a low voltage. Therefore, the direction of the dipole  205  in the nanowell  150   a   1  is from the electrode  140 A_ 1  to the electrode  140 B_ 1  from lower right to upper left). Similarly, the nanowell  150   a   2  is surrounded by the electrode  140 A_ 1 . the electrode  140 B_ 2 , and the electrodes  140 C_ 1  and  140 C_ 3 . The electrode  140 A_ 1  is arranged on the lower left of the nanowell  150   a   2 , the electrode  140 C_ 1  is arranged on the upper left of the nanowell  150   a   2 , the electrode  140 B_ 2  is arranged on the upper right of the nanowell  150   a   2 , and the electrode  140 C_ 3  is arranged on the lower right of the nanowell  150   a   2 . Therefore, the direction of the dipole  205  in the nanowell  150   a   2  is from the electrode  140 A_ 1  to the electrode  140 B_ 2  (i.e., from lower left to upper right). 
     In the second bias mode, the electrode  140 B is arranged (or assigned) in the odd rows of the electrode array, and the electrode  140 A is arranged (or assigned) in the even rows of the electrode array. In addition, the electrode  140 B is arranged (or assigned) in the odd columns of the electrode array, and the electrode  140 A is arranged (or assigned) in the even columns of the electrode array. Furthermore, the electrodes  140 C are arranged (or assigned) in each row and each column of the electrode array. In the odd rows and the odd columns, the electrodes  140 B and  140 C are arranged alternately. In the even rows and the even columns, the electrodes  140 A and  140 C are arranged alternately. By using the electrode  140 C, the direction of the dipole  205  in each nanowell  150  of the nanowell array  300 C can be more fixed. Moreover, by assigning electrodes  140 A,  140 B and  140 C and controlling the voltages of electrodes  140 A,  140 B and  140 C, the sum of dipoles  205  in the nanowell array  300 C is controllable, so the optical response signal distribution is controllable and the crosstalk phenomenon is also decreased. 
     In some embodiments, the voltage controller (not shown) of the image-sensing device  100  can fixedly assign the electrodes  140  disposed around each nanowell  150  as the electrodes  140 A,  140 B, or  140 C, so that the direction of dipole  205  in the nanowell  150  will not change, In some embodiments, the voltage controller (not shown) of the image-sensing device  100  may dynamically assign the electrodes  140  disposed around each nanowell  150  as the electrodes  140 A,  140 B, or  140 C, so as to change the direction of dipole  205  in the nanowell  150 . 
       FIGS. 6A through 6D  show the top views of dynamically assigning electrodes  140  around the nanowells  150  in a third bias mode according to some embodiments of the invention. By changing the voltages of at least four electrodes  140 , the direction of the dipole  205  of the object to be tested (such as the object to be tested  200  in  FIG. 1 ) is controlled in the nanowell  150 . 
       FIG. 6A  shows a schematic diagram illustrating the electrode  140  assigned at the first time t 1 . In  FIG. 6A , the electrode  140  at the lower right of the nanowell  150  is assigned as the electrode  140 A with a high voltage, and the electrode  140  at the lower left of the nanowell  150  is assigned as the electrode  140 CC with an intermediate voltage. Furthermore, the electrode  140  on the upper left of the nanowell  150  is assigned as the electrode  140 B with a low voltage, and the electrode  140  on the upper right of the nanowell  150  is assigned as the electrode  140 C with an intermediate voltage. Therefore, the direction of the dipole  205  in the nanowell  150  is from the electrode  140 A_ 1  at the lower right to the electrode  140 B_ 1  at the upper left. 
       FIG. 6B  shows a schematic diagram illustrating the electrode  140  assigned at the second time  12 . In  FIG. 6B , the electrode  140  at the lower left of the nanowell  150  is assigned as the electrode  140 A with a high voltage, and the electrode  140  at the upper left of the nanowell  150  is assigned as the electrode  140 CC with an intermediate voltage. Furthermore, the electrode  140  on the upper right of the nanowell  150  is assigned as the electrode  140 B with a low voltage, and the electrode  140  on the lower right of the nanowell  150  is assigned as the electrode  140 C with an intermediate voltage. Therefore, the direction of the dipole  205  in the nanowell  150  is from the electrode  140 A_ 1  at the lower left to the electrode  140 B_ 1  at the upper right. In other words, compared to  FIG. 6A , the direction of dipole  205  is rotated 90 degrees clockwise. 
       FIG. 6C  shows a schematic diagram illustrating the electrode  140  assigned at the third time t 3 , in  FIG. 6C , the electrode  140  on the upper left of the nanowell  150  is assigned as the electrode  140 A with a high voltage, and the electrode  140  on the upper right of the nanowell  150  is assigned as the electrode  140 CC with an intermediate voltage. Furthermore, the electrode  140  at the lower right of the nanowell  150  is assigned as an electrode  140 B with a low voltage, and the electrode  140  at the lower left of the nanowell  150  is assigned as an electrode  140 C with an intermediate voltage. Therefore, the direction of the dipole  205  in the nanowell  150  is from the electrode  140 A_ 1  at the upper left to the electrode  140 B_ 1  at the lower right. In other words, compared to  FIG. 6B , the direction of dipole  205  is rotated 90 degrees clockwise. 
       FIG. 6D  shows a schematic diagram illustrating the electrode  140  assigned at the fourth time t 4 . In  FIG. 6D , the electrode  140  at the upper right of the nanowell  150  is assigned as the electrode  140 A with a high voltage, and the electrode  140  at the upper left of the nanowell  150  is assigned as the electrode  140 C with an intermediate voltage. Furthermore, the electrode  140  at the lower left of the nanowell  150  is assigned as the electrode  140 B with a low voltage, and the electrode  140  at the lower right of the nanowell  150  is assigned as the electrode  140 CC with an intermediate voltage. Therefore, the direction of the dipole  205  in the nanowell  150  is from the electrode  140 A_ 1  at the upper right to the electrode  140 B_ 1  at the lower left. In other words, compared to  FIG. 6C , the direction of dipole  205  is rotated 90 degrees clockwise. 
     Referring to  FIGS. 6A through 6D  together, by periodically assigning the fur electrodes  140  to the corresponding voltages at the first time t 1 , the second time t 2 , the third time t 3 , and the fourth time t 4  in sequence, the dipole  205  in the nanowell  150  is rotated, for example, in a clockwise direction. It should be noted that a first time difference Δt 1  from the first time t 1  to the second time t 2  is the same as a second time difference Δt 2  from the second time t 2  to the third time t 3 , and the second time difference Δt 2  is the same as a third time difference Δt 3  from the third time t 3  to the fourth time t 4 . Furthermore, when the dipole  205  rotates, the image-sensing cell  104  can detect the change of the object to be tested, and then obtain the dipole moment and the moment of inertia of the object to be tested. Therefore, the image-sensing device  100  can identify the object to be tested more quickly according to the characteristics of the object to be tested. 
       FIGS. 7A through 7D  show the top views of dynamically assigning electrodes  140  around the nanowell  150  in a fourth bias mode according to some embodiments of the invention. By changing the voltages of at least four electrodes  140 , the direction of the dipole  205  of the object to be tested (such as the object to be tested  200  in  FIG. 1 ) is controlled in the nanowell  150 . 
       FIG. 7A  shows a schematic diagram illustrating the electrode  140  assigned at the fifth time t 5 . In  FIG. 7A , the electrodes  140  at the lower right and lower left of the nanowell  150  are assigned as the electrodes  140 A and  140 AA with a high voltage, respectively. Furthermore, the electrodes  140  on the upper left and upper right of the nanowell  150  are respectively assigned as the electrodes  140 B and  140 BB with a low voltage. Therefore, the direction of the dipole  205  in the nanowell  150  is from below to upward. 
       FIG. 7B  shows a schematic diagram illustrating the electrode  140  assigned at the sixth time t 6 . In  FIG. 7B , the electrodes  140  at the lower left and the upper left of the nanowell  150  are assigned as the electrodes  140 A and  140 AA with a high voltages, respectively. Furthermore, the electrodes  140  on the upper right and lower right of the nanowell  150  are respectively assigned as the electrodes  140 B and  140 BB with a low voltage. Therefore, the direction of dipole  205  in the nanowell  150  is from the left to the right. In other words, compared to  FIG. 7A , the direction of dipole  205  is rotated 90 degrees clockwise. 
       FIG. 7C  shows a schematic diagram illustrating the electrode  140  assigned at the seventh time t 7 . In  FIG. 7C , the upper left and upper right electrodes  140  of the nanowell  150  are respectively assigned as the electrodes  140 A and  140 AA with a high voltage. Furthermore, the electrodes  140  at the lower right and the lower left of the nanowell  150  are respectively assigned as the electrodes  140 B and  140 BB with a low voltage. Therefore, the direction of dipole  205  in nanowell  150  is from above to below. In other words, compared to  FIG. 7B , the direction of dipole  205  is rotated 90 degrees clockwise. 
       FIG. 7D  shows a schematic diagram illustrating the electrode  140  assigned at the eighth time t 8 . In  FIG. 7D , the electrodes  140  on the upper right and the lower right of the nano ell  150  are respectively assigned as the electrodes  140 A and  140 AA with a high voltage. Furthermore, the electrodes  140  at the lower left and the upper left of the nanowell  150  are respectively assigned as the electrodes  140 B and  140 BB with a low voltage. Therefore, the direction of the dipole  205  in the nanowell  150  is from the right to the left. In other words, compared to  FIG. 7C , the direction of dipole  205  is rotated 90 degrees clockwise. 
     Referring to  FIGS. 7A through 7D  together, by periodically assigning four electrodes  140  to the corresponding voltages at the fifth time t 5 , the sixth time t 6 , the seventh time t 7 , and the eighth time t 8  in sequence, the dipole  205  in the nanowell  150  is rotated. For example, rotate clockwise. It should be noted that a fourth time difference Δt 4  from the fifth time t 5  to the sixth time t 6  is the same as a fifth time difference Δt 5  from the sixth time t 6  to the seventh time t 7 , and the fifth time difference Δt 5  is the same as a sixth time difference Δt 6  from the seventh time t 7  to the eighth time t 8 . Furthermore, when the dipole  205  rotates, the image-sensing cell  104  can detect the change of the object to be tested, and then obtain the dipole moment and the moment of inertia of the object to be tested. Therefore, the image-sensing device  100  can identify the object to be tested more quickly according to the characteristics of the object to be tested. 
     In some embodiments, the voltage controller (not shown) of the image-sensing device  100  can assign the bias voltage of the electrodes  140  flexibly according to the configuration of the electrode  140  shown in the third bias mode of  FIGS. 6A through 6D  and the fourth bias mode of  FIGS. 7A through 7D , so as to control the direction (clockwise or counterclockwise) and angle (45 degrees, 90 degrees, 135 degrees, etc.) of the rotation of the dipole  205 . In addition, in some embodiments, the voltage controller (not shown) of the image-sensing device  100  can divide the nanowell array into multiple regions, and the electrode  140  in each region corresponds to a respective bias mode. 
       FIG. 8  shows a cross-sectional view of the nanowell  150  and the surrounding electrodes  140  according to some embodiments of the invention. In  FIG. 8 , the electrode  140  on the left of the nanowell  150   a  is assigned as the electrode  140 B with a low voltage, and the electrode  140  on the right of the nanowell  150   a  is assigned as the electrode  140 A with a high voltage. Therefore, the direction of the dipole  205  in the nanowell  150   a  is from the right electrode  140 A to the left electrode  140 B. In addition, the electrode  140  on the left of the nanowell  150   b  is assigned as the electrode  140 A with a high voltage, and the electrode  140  on the right of the nanowell  150   b  is assigned as the electrode  140 B with a low voltage. Therefore, the direction of the dipole  205  in the nanowell  150   b  is from the electrode  140 A on the left to the electrode  140 B on the right. 
       FIGS. 9A through 9F  show cross-sectional views illustrating a semiconductor structure forming the image-sensing device  100  according to some embodiments of the invention. 
     As shown in the cross-sectional view of  FIG. 9A . the image sensor array  110  is formed on the substrate  102 , and the image sensor array  110  is formed by a plurality of image-sensing cells  104 . In some embodiments, some components of the image-sensing cell  104  are formed in the substrate  102 . In addition, the dielectric layer  115  is formed on the image sensor array  110 , and the interconnect structure  120  is disposed in the dielectric layer  115 . As described above, the interconnect structure  120  includes a plurality of conductive layers  122 ,  124 , and  126 . Furthermore, the passivation layer  125  is formed on the dielectric layer  115 . 
     As shown in the cross-sectional view of  FIG. 9B , the dielectric layer  135  is formed on the passivation layer  125 . In some embodiments, the dielectric layer  115  and the dielectric layer  135  are formed of the same dielectric material. In some embodiments, the dielectric layer  115  and the dielectric layer  135  are formed of different dielectric materials. Moreover, the dielectric layer  115  and the dielectric layer  135  are formed by a deposition process. 
     As shown in the cross-sectional view of  FIG. 9C , a mask (not shown) is used to perform an etching process on the dielectric layer  135 , the passivation layer  125 , and the dielectric layer  115 , so as to form the trench  137 . Furthermore, the bottom of the trench  137  exposes the upper surface of the conductive layer  126  of the interconnect structure  120 . 
     As shown in the cross-sectional view of  FIG. 9D , a conductive material (such as tungsten) is filled into the trench  137  to form the electrode  140 . As described above, the electrode  140  is contact with and electrically connected to the conductive layer  126  of the interconnect structure  120 . In some embodiments, the electrode  140  may be the via. 
     As shown in the cross-sectional view of  FIG. 9E , a top dielectric layer  135 T is formed on the dielectric layer  135  and the electrode  140 . In some embodiments, the dielectric layer  135  and the top dielectric layer  135 T are formed of the same dielectric material. In addition, the top dielectric layer  135 T is formed by a deposition process. By forming the top dielectric layer  135 T on the electrode  140 , the electrode  140  can be prevented from being electrically connected to other structures (not shown) on the upper layer. 
     As shown in the cross-sectional view of  FIG. 9F , a mask (not shown) is used to perform an etching process on the dielectric layer  135  and the top dielectric layer  135 T to form a nanowell  150 . As previously described, there is a depth (or thickness) DI between the bottom surface  157  of the nanowell  150  and the opening  155 , and the dielectric layer  135  has a depth D 2  greater than the depth D 1 , that is, D 2 &gt;D 1 . Therefore, in the image-sensing device  100  of  FIG. 9F , the biasable electrodes  140  are formed between the nanowells  150 . In some embodiments, each nanowell  150  corresponds to a respective image-sensing cell  104 . In some embodiments, each nanowell  150  corresponds to a plurality of image-sensing cells  104 . 
       FIG. 10  shows a cross-sectional view of a semiconductor structure forming the image-sensing device  100  according to some embodiments of the invention. In some embodiments, after completing the structure of  FIG. 9F , a passivation layer  160  is further formed on the top dielectric layer  135 T and the nanowell  150 . By forming the passivation layer  160  in the nanowell  150 , it is possible to prevent the sample solution (or chemical liquid)  210  from corroding the dielectric layer  135 . 
     According to the embodiments of the invention, by controlling the bias voltage of the electrodes  140 , different electric field strengths are formed in the individual nanowells  150 , thereby controlling the dipole moment of the object to be tested  200 . In addition, the structure of the nanowell  150  and the material of the dielectric layer  135  also affect the electric field strength. Compared with traditional image-sensing devices that cannot apply an electric field to the nanowell or can only apply an electric field to the entire nanowell array, the embodiments of the invention provides an individual electric field for each nanowell by changing the bias voltage of the electrodes  140 , to detect whether the light signal intensity and spatial distribution of the light emitted by the object to be tested  200  are stable by the image sensing cell  104 , so as to obtain the relaxation time. Next, the image-sensing device  100  obtains the dipole moment and the moment of inertia of the object to be tested  200  according to the relaxation time corresponding to different electric field strengths. Then, according to the ratio of the dipoles moment and the moment of inertia, the image-sensing device  100  can obtain additional information to accelerate the identification of the object to be tested  200 . 
     While the invention has been described by way of example and in terms of the preferred embodiments, it should be understood that the invention is not limited to the disclosed embodiments. On the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.