Capacitive sensing array device with high sensitivity and electronic apparatus using the same

A capacitive sensing array device of an electronic apparatus includes sensing electrodes, a shielding conductor layer, a coupling signal source, a constant voltage source and switch modules. The coupling signal source provides a coupling signal coupled to an object. The constant voltage source provides a constant voltage to the shielding conductor layer to form a stable vertical parasitic capacitor between the shielding conductor layer and each sensing electrode. Each switch module is electrically connected to the constant voltage source via the corresponding sensing electrode. When one sensing electrode is selected to perform sensing, the corresponding switch module is configured as an open-circuited state such that the selected sensing electrode is disconnected from the constant voltage source, while the other sensing electrodes are electrically connected to the constant voltage source to form a stable horizontal parasitic capacitor between the selected sensing electrode and the other sensing electrodes.

This application claims priority of No. 101137686 filed in Taiwan R.O.C. on Oct. 12, 2012 under 35 USC 119, the entire content of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a capacitive sensing array device and an electronic apparatus using the same, and more particularly to a capacitive sensing array device with high sensitivity and an electronic apparatus using the same.

2. Related Art

The conventional capacitive sensing technology for sensing the skin of the human body may be applied to, for example, the fingerprint sensor for sensing finger's textures or a capacitive touch panel or a capacitive touch screen.

More particularly, the basic structure of the portion of the sensor in contact with the skin's texture to sense the skin's texture is an array-type sensing member. That is, several sensing members with the same structures constitute a two-dimensional array sensor. When a finger is placed on the array sensor, for example, the ridge of the finger's texture is in direct contact with the array sensor, and the valley of the finger's texture is separated from the array sensor by a gap, so that the two-dimensional capacitive image of the finger's texture may be captured, and this is the basic principle of the capacitive skin texture sensor.

In the most frequently seen sensing member structure, due to the electroconductive property of the human body, the skin in contact with the sensor may be regarded as an equal-potential electrode plate and each sensing member may be regarded as a plate electrode, so that a capacitor is formed between each sensing member and the skin. The materials disposed between the electrode plates include the cuticle on the surface of the finger's skin and a sensor protection layer disposed on the sensing electrode and in contact with the skin. The protection layer may be a single insulating layer or may contain multiple insulating layers and must have the environment-corrosion-resistant property, the impact-resistant property, the wearing-resistant property, the electrostatic-discharge-resistant property and the like.

In order to achieve the above-mentioned properties of the protection layer, one direct method is to increase the thickness of the protection layer. However, the too-thick protection layer causes the very small sensing capacitance, thereby decreasing the sensitivity.

FIG. 1is a schematic illustration showing an assembled structure of a conventional capacitive fingerprint sensor500. As shown inFIG. 1, the conventional capacitive fingerprint sensor500is usually manufactured in two stages. In the first stage of manufacturing a fingerprint sensing chip510, semiconductor manufacturing processes are utilized to form sensing members514and chip bonding pads515on a semiconductor substrate511, and then a chip protection layer512is formed on the sensing members514to provide the protective and impact-resistant properties. In the second stage, which is a packaging stage, the fingerprint sensing chip510is placed on a package substrate520, multiple wires530are bonded to the chip bonding pads515and package bonding pads525by way of wire bonding, and than a package protection layer (or referred to as a molding compound layer)540is provided to cover the wires530and the bonding pads515and525, and only the region with the sensing member array is exposed. Such conventional package processes require a special mold and a special process flow to protect the sensing member region from being covered by the molding compound and need a special machine. So, the cost is high.

In the existing IC wire-bonding technology, the distance from the chip surface513to the package surface523is greater than or equal to about 100 microns (um). Taking the fingerprint sensor with the specification of 500 DPI as an example, the area of each sensing member514is about 50 um×50 um. If the molding compound is to deploy on the sensing member, according to the dielectric constant of the commercial molding compound, the calculated capacitance of the sensing member is smaller than about 1 fF, which is too small to design a sensing circuit. If the thickness control of the package substrate, the thickness control of the chip and the like are considered at the same time, this distance further causes the great sensing error.

Thus, the conventional package protection layer540cannot be disposed above and cannot cover the sensing member514. So, the chip protection layer512has to be formed in the first stage, and the thickness (about 1 to 20 microns) of the chip protection layer512cannot be too thick to affect the sensing capacitance. Consequently, in addition to the high cost, it is a great challenge to the requirements on the environment-corrosion-resistant property, the impact-resistant property, the wearing-resistant property, the electrostatic-discharge-resistant property and the like of the sensor.

FIG. 2is a schematic illustration partially showing sensing electrodes of a conventional capacitive fingerprint sensor600. As shown inFIG. 2, in addition to the sensing capacitor Cf between each sensing electrode610of the capacitive fingerprint sensor600and the finger F, a parasitic capacitor Cp1is present when viewed from the sensing electrode610to the inside of the chip. In addition, because the sensor device is an array device having a plurality of sensing members, a parasitic capacitor Cp2is also present between each of the sensing electrodes610and each of its neighboring sensing electrodes610. These parasitic capacitors are in the fluctuating states. This non-constant parasitic capacitor interferes with the measurement, and is one of the main reasons of the incapability of achieving the high sensitivity. In order to achieve the sensitivity of Cf smaller than 1 fF, the solution of the interference between Cp1and Cp2is the most important issue.

SUMMARY OF THE INVENTION

It is therefore an object of the invention to provide a capacitive sensing array device with high sensitivity and an electronic apparatus using the same, in which the influence of the parasitic capacitor can be eliminated, and the high sensitivity property can be provided when the thick protection layer is present.

Another object of the invention is to provide a capacitive sensing array device with the high sensitivity and the gain adjustment of the sensing member, and an electronic apparatus using the same, in which the property difference caused by the manufacturing tolerance can be eliminated, and the uniformity of the images obtained by the sensor device can be enhanced.

To achieve the above-identified objects, the invention provides a capacitive sensing array device with high sensitivity. The capacitive sensing array device includes sensing electrodes, a shielding conductor layer, a coupling signal source, a constant voltage source and switch modules. The sensing electrodes are separately arranged in an array. Each of the sensing electrodes and an object form a sensing capacitor. The shielding conductor layer is disposed below the sensing electrodes. The coupling signal source provides a coupling signal coupled to the object. The constant voltage source provides a constant voltage to the shielding conductor layer so that a stable vertical parasitic capacitor is formed between the shielding conductor layer and each of the sensing electrodes. Each of the switch modules is electrically connected to the constant voltage source via a corresponding one of the sensing electrodes. When one of the sensing electrodes is selected to perform sensing, the switch module corresponding to the selected sensing electrode is configured as an open-circuited state such that the selected sensing electrode is disconnected from the constant voltage source, while the other sensing electrodes are electrically connected to the constant voltage source via the other corresponding switch modules configured as short-circuited states, so that a stable horizontal parasitic capacitor is formed between the selected sensing electrode and the other sensing electrodes.

The invention also provides an electronic apparatus including a body, a display, a capacitive sensing array device, a housing and a processor. The display is mounted on the body and displays a frame. The capacitive sensing array device is mounted on the body. The housing is mounted on the body and covers the display and the capacitive sensing array device, wherein the capacitive sensing array device senses a pattern of the object via the housing. The processor is electrically connected to the capacitive sensing array device and the display, processes the pattern of the object and interacts with a user through the display.

With the capacitive sensing array device of the invention, even if the capacitive sensing array device is covered by the protection layer and the houing in contact with the finger, the high sensitivity still can be obtained, and the sensed result cannot be affected by the parasitic capacitor. Furthermore, the uniformity of the sensed image can be further enhanced according to the self gain adjustment.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3is a schematic illustration showing a structure of a capacitive sensing array device1according to a first embodiment of the invention.FIG. 4is a schematic illustration partially showing a structure design of sensing electrodes of the capacitive sensing array device1according to the first embodiment of the invention.FIG. 5is a schematic illustration showing a single sensing member and its corresponding sensing circuit of the capacitive sensing array device1according to the first embodiment of the invention. Referring toFIGS. 3 to 5, the capacitive sensing array device1of this embodiment includes sensing electrodes10, a shielding conductor layer20, a coupling signal source30, a constant voltage source40, switch modules50, a semiconductor substrate65, a package substrate70, wires72and a package protection layer73.

The sensing electrodes10, the shielding conductor layer20, the coupling signal source30, the constant voltage source40and the switch modules50may constitute a portion of a sensing member67or the whole sensing member, and are formed in the semiconductor substrate65. Herein, the manufacturing processes applied to the semiconductor substrate include complete front-end and post-end semiconductor manufacturing processes, such as the transistor device manufacturing processes and the wire connecting processes. In this embodiment, these structures are manufactured using, for example, but without limitation to, semiconductor manufacturing processes (e.g., CMOS processes), so that the manufacturing cost is significantly decreased. The semiconductor substrate65is disposed on the package substrate70. Multiple first bonding pads71on the package substrate70may be electrically connected to multiple second bonding pads66on the semiconductor substrate65through the wires72by way of wire bonding to provide the input/output interface for the signal and the power of the package product. The package protection layer73is implemented using a molding compound, typically used in the package, to cover the semiconductor substrate65, the wires72, the first bonding pads71and the second bonding pads66. In one example, the material of the package protection layer73includes the epoxy resin serving as the molding compound (molding compound), and the package protection layer73has the thickness greater than or equal to 100 um, and the hardness greater than 5H, so that the wearing-resistant property, the electrostatic-discharge-resistant property, the impact-resistant property and the like may be provided. In addition, the package protection layer73has an exposed surface74in contact with an object F, wherein the exposed surface74is a flat surface, and the overall exposed surface74serves as a complete upper flat surface of the capacitive sensing array device1without the concave surface ofFIG. 1. Thus, the requirements of the full flat surface device can be satisfied.

Regarding the detailed structure of the sensing member67, these sensing electrodes10are separately arranged in an array including, without limitation to, a one-dimensional array or a two-dimensional array. Each sensing electrode10and the object F form a sensing capacitor Cf. In this example, the object is a finger. However, the invention is not restricted thereto. Any device operating according to the capacitive sensing principle may be used as the sensing array device of the invention.

The shielding conductor layer20is disposed below the sensing electrodes10. The shielding conductor layer20and each sensing electrode10form a vertical parasitic capacitor Cp1. The shielding conductor layer20may be a piece of conductor layer, may also be multiple conductor layers, and may correspond to the sensing electrodes10in a one-to-one, one-to-many or many-to-one manner so as to provide the constant parasitic capacitor.

InFIG. 4, the middle sensing electrode10and its surrounding members also form a horizontal parasitic capacitor Cp22. These horizontal parasitic capacitors Cp22are equivalent to a horizontal parasitic capacitor Cp2inFIG. 5. Thus, the sensing electrode10and its neighboring sensing electrodes10form the horizontal parasitic capacitor Cp2.

The shielding conductor layer20and the sensing electrodes10may be formed using the metal manufacturing process of the semiconductor manufacturing processes. The material between the shielding conductor layer20and the sensing electrodes10may contain a single-layer or multiple inter-metal dielectrics (IMD) layers. The sensing members may be formed using multiple metal and IMD manufacturing processes of the semiconductor manufacturing processes.

The coupling signal source30is coupled to the object F and provides a coupling signal Vdrive coupled to the object F. The coupling signal Vdrive may be directly or indirectly coupled to the object F, wherein the direct coupling may transfer the coupling signal to the object F using a conductor in contact with the object F, and the indirect coupling may be implemented by disposing a dielectric layer between the conductor and the object F. Since the direct coupling and the indirect coupling are well known in the art, detailed descriptions and restrictions thereof will be omitted.

The constant voltage source40provides a constant voltage to the shielding conductor layer20so that a stable vertical parasitic capacitor Cp1is formed between the shielding conductor layer20and each sensing electrode10. In this embodiment, the grounding voltage (GND) of 0V serves as the constant voltage. However, the invention is not restricted thereto, the constant voltage may also be equal to 3.3V, 5V or the like to achieve the effect of the invention. However, it is to be noted that the constant voltage source must provide the very stable voltage, which cannot fluctuate under the external interference. This is because the fluctuating voltage would decrease the sensitivity of the sensing member.

These switch modules50are only represented by T0and T1inFIGS. 4 and 5, and these switch modules50are electrically connected to the constant voltage source and these sensing electrodes10in a one-to-one manner. When one sensing electrode10is selected to perform the sensing, the switch modules50are configured such that an open-circuited state is formed between the sensing electrode10and the constant voltage source40, while the short-circuited state is formed between the other sensing electrodes10and the constant voltage source40, so that a stable horizontal parasitic capacitor Cp2is formed between the selected sensing electrode10and the other sensing electrodes10, and that the output of the capacitive sensing array device1does not relate to the horizontal parasitic capacitor Cp2and the vertical parasitic capacitor Cp1(see the following derivation). The switch module50may be implemented by, for example but without limitation to, a transistor or any other suitable means. InFIGS. 4 and 5, when the middle sensing electrode10is selected to perform the sensing, the switch module T0is in the open-circuited state, and the switch module T1is in the short-circuited state (i.e., turned-on state). Consequently, the surrounding sensing electrodes10are grounded (or coupled to the constant voltage), while the bottom shielding conductor layer20is set as the grounded state (or coupled to the constant voltage). As a result, a stable shielding environment may be provided to completely surround the sensing electrode therein. Although a relatively large parasitic capacitor is still present between the sensing electrode and the neighboring shielding environment, this parasitic capacitor is different from the conventional design and has a constant and stable capacitance value. This is advantageous to the design of the sensing circuit, and is also a key point of the invention.

As shown inFIG. 5, the capacitive sensing array device1may further include reading circuits60, which are electrically connected to the sensing electrodes10and output multiple output signals Vout, respectively. In this embodiment, in order to prevent the signal of each sensing electrode from being transmitted too far and interfered, each sensing member is configured to be connected to an operational amplifier for amplifying the sensing signal on site. Thus, the invention is free from the interference caused by the too-long transmission line (array device's usual issue). Therefore, each reading circuit60includes an operational amplifier61, a tunable capacitor62and a reset switch PH0.

All or a portion of the operational amplifier61may be formed under the sensing electrode10, and one sensing electrode10may correspond to one operational amplifier61. Of course, multiple sensing electrodes10may also correspond to one operational amplifier61. The operational amplifier61has a positive input terminal61A, a negative input terminal61B and an output terminal61C. The negative input terminal61B is electrically connected to the sensing electrode10, and the positive input terminal61A is electrically connected to a reference voltage Vref. The tunable capacitor62has a first terminal62A electrically connected to the negative input terminal61B, and a second terminal62B electrically connected to the output terminal61C. In this example, the tunable capacitor62is constituted by a capacitor Ch and a switch S. In this example, because only one capacitor Ch is provided, the switch S may be removed. The reset switch PH0and the tunable capacitor62are connected in parallel.

According to the circuit diagram ofFIG. 5, the output signal Vout may be derived according to the electrical charge conservation principle.

When Vdrive=0, the reset switch PH0is in the short-circuited state, and the charge Q1at the node A may be represented by:
Q1=Cf×(Vref−Vdrive)+Cp×Vref=Cf×Vref+Cp×Vref.

When Vdrive is high, the reset switch PH0is in the open-circuited state, and the charge Q2at the node A may be represented by:
Q2=Cf×(Vref−Vdrive)+Cp×Vref+Ch×(Vref−Vout).

According to the electrical charge conservation principle, Q1=Q2may be obtained.

The expression may be simplified as:
Cf×Vdrive−Ch×Vref=−Ch×Vout.

Then, it is obtained:
Vout=Vref−(Cf/Ch)×Vdrive,
wherein Cp=Cp1+Cp2. According to the above-mentioned equation, it is found that the output signal Vout does not relate to the parasitic capacitors Cp1and Cp2. As mentioned hereinabove, the feature of the invention is to stabilize the fluctuating value of the parasitic capacitor, which fluctuates due to the uncontrolled surrounding environment, so that the parasitic capacitor may be naturally neglected under the operation principle of the operational amplifier sensing circuit. In addition, Cf/Ch is a gain. In the practical design, Ch is as small as possible because the sensing signal may be amplified in each independent sensing member so that the sensing signal cannot be interfered in the transmission line to affect the signal quality. In one embodiment of the invention, Vdrive is equal to 3.3V, Vref is equal to 1.8V, and Ch ranges from 1 to 4 fF. However, the invention is not particularly restricted thereto.

FIG. 6is a schematic circuit diagram showing a single sensing member and its corresponding sensing circuit of a capacitive sensing array device1according to a second embodiment of the invention. As shown inFIG. 6, this embodiment is similar to the first embodiment except for the difference that the tunable capacitor62includes reference capacitors Ch1to CHn connected to the negative input terminal61B and the output terminal61C in parallel through multiple reference switches S1to Sn, respectively. The capacitance of the tunable capacitor62may be adjusted by controlling the open-circuited states and the short-circuited states of the reference switches S1to Sn.

In this example, the capacitive sensing array device1may further include a reference switch controller80, which is electrically connected to the reference switches S1to Sn, and controls the open-circuited states and the short-circuited states of the reference switches S1to Sn. The reference switch controller80may turn on one of the reference switches S1to Sn at a time. In this condition, the reference capacitors Ch1to CHn are preferably configured to have multiple capacitances. Alternatively, the reference switch controller80may also turn on multiple ones of the reference switches S1to Sn at a time. In this condition, these reference capacitors Ch1to CHn have the same capacitance value. Of course, the reference capacitors Ch1to CHn may also have different capacitance values. The short-circuited states or the open-circuited states of the reference switches S1to Sn may also be controlled by another control unit.

Instead of sharing one gain adjusting unit by the sensing members, the self gain adjustment is present in each sensing member. So, the signal may be transmitted by a long distance without being interfered by the noise caused by the external traces. Because the manufacturing tolerance does exist, the protection layer with the designed thickness of 100 um may have the thickness ranging from 80 to 130 um. Using the self gain adjustment, it is possible to eliminate the problem caused by the difference between the manufacturing processes, and to effectively enhance the image uniformity and sensitivity adjustment. This is the most important issue for any sensing member array. The gain of each sensing member may be independently adjusted to achieve the uniform image and signal intensity.

FIG. 7is a control timing chart of the single sensing member of the capacitive sensing array device1according to the second embodiment of the invention. As shown inFIG. 7, in the duration from time t0to t1, the switch T0is set as the open-circuited state, the switch T1is set as the short-circuited state, and the switch PH0is set as the short-circuited state. At this time, the coupling signal Vdrive has the low level (0V in this embodiment), and this stage is the pre-charge operation of the operational amplifier of the sensing member. Then, in the duration from time t1to t2, Vdrive is set to the high level (3.3V in this embodiment), the switch T0continuously keeps in the open-circuited state, the switch T1continuously keeps in the short-circuited state, but the switch PH0switches to the open-circuited state. In this stage, the sensing operation of the sensing electrode10corresponding to the switch T0is started by way of charge sharing, and the sensed result is amplified to obtain Vout by the operational amplifier inside the single sensing member. Similarly, each of the next sensing members also performs the operation mentioned hereinabove, so that the signals of the sensing member array can be completely read out. The output signal Vout represents the condition of the operation of each single sensing member and the to-be-tested object F.

FIG. 8is a schematic illustration showing an electronic apparatus200according to the embodiment of the invention.FIG. 9is a cross-sectional view taken along a line9-9ofFIG. 8. Referring toFIGS. 8 and 9, the electronic apparatus200of the invention includes a body210, a display220, a capacitive sensing array device1, a housing230and a processor240. The display220mounted on the body210displays a frame. The capacitive sensing array device1is mounted on the body210. The housing230is mounted on the body210and covers the display220and the capacitive sensing array device1. The capacitive sensing array device1senses the pattern of the object F via the housing230. The processor240, electrically connected to the capacitive sensing array device1and the display220, processes the pattern of the object F and interacts with a user through the display220. The housing230may be transparent or opaque, and may also be, for example but without limitation to, an upper cover, a lower cover or a side cover of the electronic apparatus.

FIG. 10is a schematic illustration showing another electronic apparatus200A according to the embodiment of the invention. As shown inFIG. 10, the electronic apparatus200A is similar to the electronic apparatus200ofFIG. 8except for the difference that the capacitive sensing array device1A is exposed outside to function as a main button and an arrow button of the electronic apparatus200A to facilitate the user recognizing at the button region. Thus, in addition of the provision of the function of sensing the object, the capacitive sensing array device may further provide the button function so that the user can input a control instruction, including, for example but without limitation to, the selection and movement instructions, through the capacitive sensing array device.

With the capacitive sensing array device of the invention, even if the capacitive sensing array device is covered by the protection layer and the housing in contact with the finger, the high sensitivity still can be obtained, and the sensed result cannot be affected by the parasitic capacitor. Furthermore, the uniformity of the sensed image can be further enhanced according to the self gain adjustment.