CN106156710B - The method and fingerprint sensor for improveing capacitance type fingerprint sensing unit, obtaining fingerprint - Google Patents

The method and fingerprint sensor for improveing capacitance type fingerprint sensing unit, obtaining fingerprint Download PDF

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Publication number
CN106156710B
CN106156710B CN201510186265.XA CN201510186265A CN106156710B CN 106156710 B CN106156710 B CN 106156710B CN 201510186265 A CN201510186265 A CN 201510186265A CN 106156710 B CN106156710 B CN 106156710B
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voltage
fingerprint sensing
charging
metal
capacitor
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CN201510186265.XA
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CN106156710A (en
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林继周
和正平
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旭景科技有限公司
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Abstract

The present invention provides a kind of method and fingerprint sensor for improveing capacitance type fingerprint sensing unit, obtaining fingerprint.The improvement capacitance type fingerprint sensing unit includes substrate framework and fingerprint sensing framework.Fingerprint sensing framework has the first metal intermetallic dielectric layer, second metal layer, the second metal intermetallic dielectric layer, third metal layer and passivation layer.By connection third metal layer to transient voltage suppressing device, anti-electrostatic-discharge effect can get.By increasing the thickness of the first metal intermetallic dielectric layer and the second metal intermetallic dielectric layer, the sensitivity of improvement capacitance type fingerprint sensing unit, which can get, to be improved.

Description

The method and fingerprint sensor for improveing capacitance type fingerprint sensing unit, obtaining fingerprint

Technical field

The present invention relates to fingerprint sensing technology fields, more particularly to a kind of improvement capacitance type fingerprint sensing unit, obtain The method and fingerprint sensor of fingerprint.

Background technique

For security purposes, there are many physiological characteristics of people can be used as personal identification, these features such as fingerprint, view Nethike embrane, iris, DNA even face feature.For those can distinguish the device of certain physiological characteristics of everybody, fingerprint is passed Sensor has minimum cost and complexity, and identification result is generally all well.In addition, needed for the details of one fingerprint of storage The data volume wanted is few (from 120 bytes to 2K byte).This point is so that fingeprint distinguisher all widely connects in many fields By with use.

The detection technology of existing numerous species can be used for obtaining fingerprint, at present commonly optical profile type and capacitive sensing Technology.Optical fingerprint sensing module utilize from finger detecting face reflected light intensity, distinguish finger contact portion what Place is spine, and where is valley.The advantages of optical profile type technology is reliability and low cost.However, since built-in optical formula is saturating The limitation of the size of mirror, so that the shape of optical fingerprint sensing module can not reduce, such optical sensor is difficult to embedding In portable equipment.On the other hand, capacitance type fingerprint identification module is made of silicon chip, can be made to very compact. In some cases, as soon as when fingermark image can be obtained by slip scan, fingerprint sensor can also become thinner with more It is small.The small external form of capacitance type fingerprint identification module makes it suitable for portable type application product, such as gate inhibition's armband, bank Card, mobile phone, tablet computer or USB adapter etc..

The principle of capacitive fingerprint sensing device is that the capacitance based on two layers of parallel plate capacitor is inversely proportional to two The physical phenomenon of distance between plates.Capacitive fingerprint sensing device includes array sensing unit, each sensing unit includes that sensing is flat Plate.Wherein one layer plate of the plate as two layers of parallel plate capacitor is sensed, and human cuticular tissue is flat as another The spine of plate, finger can be positioned out from valley by the different capacitance of measurement.There are many recognize mould about capacitance type fingerprint The preceding case of block, for example, U.S. Patent No. 6114862 disclose a kind of range sensor, it has a condenser type unit, the electricity There is to appearance formula units alternately first capacitor device plate, the second capacitor plate is arranged in first capacitor device platen surface, and second The distance of capacitor plate can be measured to obtain.In the case where taking fingerprint, the second capacitor plate by finger skin Surface directly defines.The sensor includes an inverting amplifier, between the input and output of condenser type unit junction, To form negative feedback branch.By the way that using charge scale as the input of inverting amplifier, voltage scale is directly proportional to measurement Distance, and obtained at the output of inverting amplifier.Although the framework of the sensor is simple, amplifier suffers from uniformity Problem, and its energy efficiency and bad.

Another preceding case is exposed in U.S. Patent No. 7663380, please refers to Fig. 1 and Fig. 2.Capacitive fingerprint sensing device packet The C of device containing fingerprint capacitorF, reference capacitor CS, the first transistor 33, second transistor 34, third transistor 35 and the 4th transistor 36.Fingerprint capacitor device CFWith capacitor, which is a valley capacitor CFVOr spine capacitor CFR.Reference capacitor CSWith capacitor CS, CFV<CS<CFR.The first transistor 33 is configured to reference capacitor CSPrecharge, second transistor 34 are configured to fingerprint Capacitor CFPrecharge, third transistor 35 are configured to reassign reference capacitor CSWith fingerprint capacitor device CFInterior charge.The Four transistors 36 are configured after reassignment, to export the C of reference capacitorSVoltage.

Fig. 1 further provides the equivalent circuit in pre-charging stage fingerprint sensor.Fingerprint is passed in pre-charging stage For sensor, selection line C is readm+1Declaration, the first transistor 33 and second transistor 34 start, and voltage VAWith VBRespectively to ginseng Examine capacitor CSWith fingerprint capacitor device CFPrecharge.Fig. 2 is shown in evaluation stage same circuit.Fingerprint is passed in evaluation stage For sensor, selection line C is readm+1Declaration, third transistor 35 starts, and is stored in reference capacitor CSWith fingerprint capacitor device CF In charge redistribute.This moment, scan line is still declared, the starting of the 4th transistor 36 reads which part is selection line be according to The fingerprint of people, i.e. spine or valley are detected simultaneously output voltage.On surface apparently, if spine is detected, selection is read The output voltage of line is larger, if valley is detected, output voltage values are smaller.Thus, fingerprint can the voltage based on output and Image goes out, and voltage is the position with finger and is changed.

However, in fact, the fingerprint acquisition apparatus as made by such capacitive fingerprint sensing device, sensitivity is not high. When having a protective layer when the top of range sensor or the range sensor are encapsulated in a mould shell, figure is taken out The quality of picture can be deteriorated.

Therefore, it in order to solve problem described above, needs a kind of capacitance type fingerprint sensing unit of improvement, obtain fingerprint Method and fingerprint sensor.

Summary of the invention

In order to overcome the deficiencies of the prior art, the present invention provides a kind of improvement capacitance type fingerprint sensing unit, obtains fingerprint Method and fingerprint sensor can get anti-electrostatic-discharge effect by connection third metal layer to transient voltage suppressing device. By increasing the thickness of the first metal intermetallic dielectric layer and the second metal intermetallic dielectric layer, the sensitive of capacitance type fingerprint sensing unit is improved Degree, which can get, to be improved.The present invention realizes that technical solution used by above-mentioned purpose is:

A kind of improvement capacitance type fingerprint sensing unit includes: substrate framework and fingerprint sensing framework, the substrate framework tool There is at least one the first metal layer and form charging circuit and operation circuit, for alternately receiving charging voltage, and assignment Into the capacitor of the operation circuit and the reception charging voltage is simultaneously stopped from the charge of the charging circuit;The fingerprint Sensing architecture is arranged on the substrate framework, includes the first metal intermetallic dielectric layer, second metal layer, the second inter-metal dielectric Layer, third metal layer and passivation layer;First metal intermetallic dielectric layer has the first depth, and first depth is greater than 3 μm;Institute It states second metal layer to be arranged in first metal intermetallic dielectric layer, and forms induction metal plate;Second inter-metal dielectric Layer is arranged in the second metal layer and around the second metal layer, and the covering induction metal plate is simultaneously deep with second Degree, second depth are greater than 3 μm;The third metal layer is arranged in second metal intermetallic dielectric layer, by being located at institute The opening shape squarely grid on induction metal plate is stated, and is connected to transient voltage suppresser device, for receiving first voltage With second voltage;The passivation layer covers the third metal layer.Wherein, the transient voltage suppressing device limit electricity is triggered Pressure value is higher than the first voltage and/or the second voltage;The substrate framework also assigns the electricity from the charging circuit For lotus into the capacitor of the fingerprint sensing framework, the charging circuit is simultaneously simultaneously stopped the reception charging voltage.

Charging capacitor is arranged in the charging circuit in one of the embodiments, for working as the charging capacitor When device receives the charging voltage, charge is stored, parasitic capacitance is present in the operation circuit, and cross capacitance is formed in Between the third metal layer and the induction metal plate.When finger is close to the passivation layer, signal capacitor is formed in the hand Finger and the third metal interlevel, and finger capacitor is formed between the finger and the induction metal plate.Assign switch setting Between the operation circuit and the charging circuit, to open and close the reception of the charging voltage and assign charge.When described When second voltage generation, the charging voltage stop applying and assignment switch is opened, output voltage changes from the charging It is obtained in circuit.

Work as VoutIt is the value of the output voltage, VddIt is the value of the charging voltage, V1With V2It is the first voltage respectively With the value of second voltage, Cr is the capacitance of the charging capacitor, CpIt is the value of the parasitic capacitance, CfIt is the finger electricity When the value and Cx of appearance are the values of the cross capacitance, the output voltage is

Discharge switch is arranged in the operation circuit in one of the embodiments, when the assignment, which switchs, closes, For the voltage of the operation circuit and the second metal layer to be reset to signal ground connection.

The invention further relates to a kind of using the improvement capacitance type fingerprint sensing unit come the method for obtaining fingerprint, includes Step: it closes and assigns switch to disconnect charging circuit and operation circuit;Apply first voltage to third metal layer, and passes through unlatching Discharge switch resets the voltage of operation circuit and second metal layer;Apply charging voltage to charging circuit;Close discharge switch with Charge switch;It opens to assign and switchs and provide second voltage to replace first voltage;Measure output voltage;And translation is from each The output voltage of capacitance type fingerprint sensing unit is improved, for the fingermark image data of the fingerprint of a part of user of correspondence.

According to another aspect of the present invention, the present invention also provides a kind of fingerprint sensors, change comprising several described Good capacitance type fingerprint sensing unit, to form fingerprint sensing array, wherein the substrate framework or fingerprint sensing framework is identical In same level, the third metal layer of all fingerprint sensing units connects to form metal grill for framework setting adjacent to each other.

The beneficial effects of the present invention are:

By connection third metal layer to transient voltage suppressing device, improveing capacitance type fingerprint sensing unit can be from electrostatic The damage of electric discharge.By increase the first metal intermetallic dielectric layer and the second metal intermetallic dielectric layer thickness, parasitic capacitance Cp with intersect The value of capacitor Cx can reduce.According to the formula of above-mentioned output voltage Vout, the sensitivity for improveing capacitance type fingerprint sensing unit can Improved.

Detailed description of the invention

Fig. 1 is equivalent circuit of the existing fingerprint sensor in pre-charging stage;

Equivalent circuit of the fingerprint sensor in evaluation stage that Fig. 2 is Fig. 1;

Fig. 3 is the schematic diagram of improvement one embodiment of capacitance type fingerprint sensing unit of the invention;

Fig. 4 is the equivalent circuit of improvement one embodiment of capacitance type fingerprint sensing unit of the invention;

Fig. 5 illustrates the physical structure of two adjacent improvement capacitance type fingerprint sensing units, is placed on it with finger, Capacitor is formed there between;

Fig. 6 is the top view of improvement one embodiment of capacitive fingerprint sensing device of the invention;

Fig. 7 is that the charge of output voltage in the present invention assigns the equivalent circuit of respective items;

Fig. 8 is the equivalent circuit of the second voltage respective items of output voltage in the present invention;

Fig. 9 is the flow chart that equivalent circuit of the invention operates;

Wherein, 1- improvement capacitive fingerprint sensing device, 10- fingerprint sensing array, 11- metal grill, 33 the first transistors, 34 second transistors, 35- third transistor, the 4th transistor of 36-, 100- improve capacitance type fingerprint sensing unit, 110- fingerprint Sensing architecture, 110a- cross capacitor, 110b- finger capacitor, 110c- signal capacitor, the first metal intermetallic dielectric layer of 111-, 112- second metal layer, the second metal intermetallic dielectric layer of 113-, 114- third metal layer, 115- passivation layer, 116- input buffering, 120- substrate framework, 121- the first metal layer, 122- charging circuit, 1221- charging capacitor, 1222- charge switch, 1223- Assign switch, 1224- buffer, 124- operation circuit, 1241- discharge switch, 124a- capacitor parasitics, 150- weld pad, 200- Finger, the first depth of d1-, the second depth of d2-, Cm+1Read selection line, VAVoltage, VBVoltage, CFFingerprint capacitor device, CS- Reference capacitor.

Specific embodiment

Present invention is further described in detail in the following with reference to the drawings and specific embodiments, but not as to limit of the invention It is fixed.

Referring to Fig. 3 to Fig. 9, Fig. 3 is a kind of sectional view of improvement capacitance type fingerprint sensing unit 100 of the invention, and Fig. 4 is The equivalent circuit of capacitance type fingerprint sensing unit 100 is improved, Fig. 5 shows two adjacent improvement capacitance type fingerprint sensing units 100, Illustrate that the equivalent condenser corresponding with being located therein of fingerprint sensing framework 110, Fig. 6 are the upper views for improveing capacitive fingerprint sensing device Figure, Fig. 7 be output voltage charge assign respective items equivalent circuit, Fig. 8 be output voltage second voltage respective items etc. Circuit is imitated, Fig. 9 is the flow chart of equivalent circuit running.

Improvement capacitance type fingerprint sensing unit 100 basically comprises fingerprint sensing framework 110 and substrate framework 120, fingerprint Sensing architecture 110 is arranged on substrate framework 120.Fingerprint sensing framework 110 has several subrack structures, they are the first gold medal respectively Dielectric layer 111, second metal layer 112, the second metal intermetallic dielectric layer 113, third metal layer 114 and passivation layer 115 between category.First Metal intermetallic dielectric layer 111 can be by common, and the processing procedure for manufacturing any metal intermetallic dielectric layer in integrated circuit is formed.No It is same as being traditionally used for the sensing unit of fingerprint sensor, the first metal intermetallic dielectric layer 111 will have certain depth.It is needed The reasons why larger depth, will discuss later.As shown in figure 3, the figure points out the first metal intermetallic dielectric layer in adjacent metal interlayer 111 the first depth is d1.First depth d1 should be greater than 3 μm, for example can be 5 μm.

Second metal layer 112 is arranged in the first metal intermetallic dielectric layer 111, acts on as an induction metal plate, the second gold medal Belong to layer 112 and adjacent object forms several capacitors (tangible or invisible capacitor).For example, shown in Fig. 5, when finger 200 is close When fingerprint sensing unit 100, second metal layer 112 and finger 200 form finger capacitor 110b.That is, second metal layer 112 be exactly the component of capacitor with finger 200, and its capacitance is with the close part of finger 200 and second metal layer 112 Between distance and change.Generally, the capacitance of finger capacitor be inversely proportional between finger 200 and second metal layer 112 away from From.

Second metal intermetallic dielectric layer 113 is arranged in second metal layer 112 and around second metal layer 112, it is covered Incude metal plate (second metal layer 112).In order to minimize capacitance (its between third metal layer 114 and second metal layer 112 Reason will be illustrated in down), it is real that the second depth d2 of the second metal intermetallic dielectric layer 113 and adjacent metal interlayer is greater than general tradition The depth of work.Second depth d2 should be greater than 3 μm, for example can be 5 μm.

Third metal layer 114 is arranged in second metal layer 112.Third metal layer 114, which passes through, is located at induction metal plate 112 On opening, form rectangular grid.In addition, third metal layer 114 is connected to transient voltage suppresser (Transient Voltage Suppressor, TVS) device (not shown).Transient voltage suppressing device is a kind of electronic building brick, quick for protecting The electronic device of sense is from the damage from the abrupt voltage wave connected wires.Transient voltage suppressing device can not refer to improvement condenser type The fingerprint sensor of line sensing unit 100 or the fingerprint sensing array comprising improveing capacitance type fingerprint sensing unit 100 is raw simultaneously Produce manufacture.Transient voltage suppressing device can be an independent component, be connected to each improvement capacitance type fingerprint sensing unit 100 Third metal layer 114.Other functions of third metal layer 114 are to receive first voltage and second voltage (V shown in Fig. 4in)。 The only limitation is that the limit voltage value of triggering transient voltage suppressing device should be higher than first voltage and/or second voltage.( In the present embodiment, after second voltage appears in first voltage, voltage drop is formed).Otherwise, any electricity higher than limit voltage value Pressure will be released to avoid the circuit destroyed in substrate framework.Thus, improvement capacitance type fingerprint sensing unit 100 need not include one Layer additional metal layer provides ESD protection function.Top layer is passivation layer 115, it has coated third metal layer 114 and has protected Each layer structure of lower section is from colliding and scratching.The voltage change as caused by first voltage and second voltage can be buffered by input 116 know.

Substrate framework 120 has at least one the first metal layer 121, at least one the first metal layer 121 provides circuit group Part, the interconnection of capacitor and switch in such as substrate framework.Pass through at least one the first metal layer 121,120 shape of substrate framework At charging circuit 122 and operation circuit 124.Charging circuit 122 is with operation circuit 124 by the dotted line frame institute of Fig. 4 electrical equivalent Describe.The main purpose of substrate framework 120 is alternately to receive stable charging voltage (Vdd), and assign and carry out self-charging circuit 122 charge is simultaneously stopped reception charging voltage to the capacitor in operation circuit 124 and fingerprint sensing framework 110.

Charging circuit 122 has built-in charging capacitor 1221, and when applying charging voltage, charging capacitor 1221 is used To store charge.The side of charging capacitor 1221 is connected to signal ground connection.Therefore, charging capacitor 1221 will be in the charging stage It is charged to burning voltage Vdd(step S03).Charging capacitor 1221 can be by circuit unit, such as MOS or Poly-to-Poly Capacitor etc. realizes that the capacitor of charging capacitor 1221 is determined by the geometry of MOS lock or polysilicon.In addition, when improvement electricity When the formation of appearance formula fingerprint sensing unit 100, or when finger 200 is close to improvement capacitance type fingerprint sensing unit 100, others etc. Imitate capacitor Cx、CpWith Cf(later will explanation) can be there is naturally.

Charging circuit 122 also has two switches: charge switch 1222 and assignment switch 1223.When charge switch 1222 is opened When opening and assigning switch 1223 and shut, charging voltage is applied to charging circuit 122,1221 (C of charging capacitorr) will be electrically charged To charging voltage Vdd.When charge switch 1222 is closed and assignment switch 1223 also remains off state, charging voltage VddConfession It should just stopped, 1221 (C of charging capacitorr) keep charging voltage Vdd.Assign switch 1223 be arranged operation circuit 124 with fill Between circuit 122, it switches the behaviour for receiving charging voltage (as described above, when charge switch 1222 is opened) and assigning charge Make.That is, charging circuit 122 and operation circuit 124 are isolated from one another when assignment switch 1223 is shut.On the other hand, when When assigning the unlatching of switch 1223, charging circuit 122 and operation circuit 124 are connected to each other, and charge can transfer therebetween, to reach The charge of Cheng Xin is evenly distributed.

Charging circuit 122 further comprises buffer 1224, and buffer 1224 is used to be isolated improvement capacitance type fingerprint sensing Unit 100 and other processing circuit (not shown), and transmit output voltage VoutTo subsequent processing circuit (not shown).It is logical For often, buffer 1224 is made of " voltage follower ".

Operation circuit 124 is arranged in substrate framework 120, but is not belonging to the common name of the assembly set of charging circuit 122 Word.In other words, any to be separated by assigning switch 1223 self-charging circuit 122, and the component being present in substrate framework 120, It is all a part of operation circuit 124.The function of operation circuit 124 by with improvement capacitance type fingerprint sensing unit 100 operation It is described below together.Operation circuit 124 has discharge switch 1241.When assigning the closing of switch 1223, discharge switch 1241 for reseting (electric discharge) for the voltage of the voltage of operation circuit 124 and second metal layer 112 as signal ground connection.Institute as above It states, several capacitors can naturally occurring.In order to which the operation to improvement capacitance type fingerprint sensing unit 100 is better understood from, own These capacitors are embodied by equivalent condenser.Parasitic capacitance is present in operation circuit 124 (in general, parasitic capacitance is formed in Incude between metal plate 112 and at least one the first metal layer 121), cross capacitance is formed in third metal layer 114 and induction gold Belong between plate 112.Therefore, capacitor parasitics 124a and cross capacitor 110a are respectively for explanation.

When finger 200 is close to passivation layer 115, signal capacitor is formed between finger 200 and third metal layer 114.This Outside, finger capacitor is formed between finger 200 and induction metal plate 112.Similarly, signal capacitor 110c and finger capacitor 110b is also respectively for explanation.Fig. 5 shows that two adjacent improvement capacitance type fingerprint sensing units 100 (are delimited by a dashed line Open), illustrate the equivalent condenser that fingerprint sensing framework 110 is located therein with each.

It is stressed that in fingerprint sensing array 10 (or fingerprint sensing area), i.e. the region of Fig. 6 dotted line frame encirclement, is by arranging Same architecture adjacent to each other being arranged in that capacitance type fingerprint sensing unit 100 is improved in array is formed in same level, and The third metal layer 114 of all improvement capacitance type fingerprint sensing units 100 is that connection forms metal grill 11.Consider to be connected with each other Third metal layer 114 the gross area more, the electricity of signal capacitor 110c bigger than respective sense plate (second metal layer 112) The capacitor held also than other fingerprint sensing framework equivalent capacitors is too many greatly, i.e. Cs>>Cx、CfOr Cp.Thus, signal capacitor 110c can regard short circuit as and ignore in the discussion below.It is improvement capacitive fingerprint sensing device 1 see Fig. 6, Fig. 6 Top view.Present invention can apply to improve on capacitive fingerprint sensing device 1, which is contained The fingerprint sensing array 10 and several input/output (I/O) weld pad 150 stated.These input/output weld pads 150 are connected to fingerprint Array 10 is sensed, for connecting with external circuit.

Capacitance type fingerprint sensing unit 100 is improved with following procedure operation, program includes unique and repeatedly stage, is asked Refering to Fig. 9.There are three the main stages: setting stage, charging stage and assignment stage.In the setting stage, assign switch 1223 (step S01) is closed so that charging circuit 122 and operation circuit 124 disconnect.

In the charging stage, firstly, first voltage V1It is applied to third metal layer 114, operation circuit 124 and the second metal The voltage of layer 112 is discharged to signal ground connection (step S02) by opening discharge switch 1241 (reseting).Then, it is filled by opening Electric switch 1222, charging voltage are applied in charging circuit 122 (step S03).In last step of charging stage, electric discharge Switch 1241 and charge switch 1222 close (step S04).It should be noted that step S02 can be exchanged with the sequence of step S03, Or it carries out simultaneously.At charging stage end, charging capacitor 1221 is charged to charging voltage Vdd, equivalent condenser is charged to One voltage V1

It is the assignment stage after the charging stage.In the assignment stage, following step is substantially while occurring: opening Assign switch 1223 and provides second voltage to replace first voltage (step S05).In fact, one of them may be than another A slightly early generation, and sequence will not influence result.When the voltage stabilization of buffer 1224, output voltage V is measuredout.It infuses Meaning is when second voltage occurs, and charging circuit 122 can obtain output voltage variation.It will be apparent that improvement capacitance type fingerprint sense The distribution for surveying charge in unit 100 will change, and further influence output voltage Vout.In fact, the influence of output voltage comes From two sources: charge is assigned and the voltage change of input 116 (differences of second voltage and first voltage) of buffering.Output voltage VoutIt is above two aggregations for carrying out source contribution voltage value, is described as follows.

In order to which the assignment stage is more fully described, equivalent circuit as shown in Figure 4 is depicted.VddIt is the value of charging voltage, V1With V2That respectively indicate is the value of first voltage and second voltage, CrIt is the capacitance of charging capacitor, CpIt is parasitic capacitance Value, CfIt is the value of finger capacitor, CxIt is the value of cross capacitance, output voltage VoutAcross charging capacitor CrVoltage value, by defeated Buffer 1224 measures out.Wherein,

By the theory of linear circuit it is found that the charge of allocated switch 1223 is assigned and driving voltage is by first voltage V1It arrives Second voltage V2The net effect of variation is the addition of voltage value, and the charge of allocated switch 1223 is assigned and driving voltage is by first Voltage V1To second voltage V2Variation be separate apply.The charge of allocated switch 1223 assigns (no first voltage V1To Two voltage V2Voltage change) equivalent circuit be depicted in Fig. 7.In input buffering, (charging capacitor Cr is not charged to VddFeelings Shape) from first voltage V1To second voltage V2The equivalent circuit of voltage drop is described in fig. 8.Enable V01It represents when assignment switch is opened When assigning the stage, VoutVoltage change, but input driving maintain identical first voltage V1.Enable V02It represents when input is slow Punching is by first voltage V1Change to second voltage V2, and charging capacitor Cr is not charged to VddWhen, VoutVoltage change.Vout's Net result will be:

Vout=V01+V02;Wherein,

And

To the parasitic capacitance C of self-assembling formationpWith cross capacitance CxFor, their value is according to physical structure and condenser type The material of fingerprint sensing unit 100 and determine.Finger capacitor CfIt is parameter, by metal layer 112 to the finger tip for touching sensor Valley or spine distance determine.Charging capacitor CrIt is formed by the circuit unit inside at least one the first metal layer 121, and At least one the first metal layer 121 can be by geometry (such as MOS transistor or the Poly-to-Poly capacitor of circuit unit Device) it is determined, circuit unit is practical to be made into charging capacitor Cr.In order to confirm to propose improvement capacitance type fingerprint sensing unit 100 Architecture design, output voltage V should be givenoutTo charging capacitor CfFirst derivative.Therefore, available:

Wherein,

It (is represented by improve sensitivity), first itemWith Section 2Must have identical Sign;In other words, if VddIt is positive value, then V2-V1It must be negative value, that is, V1>V2.This is it is also obvious that parasitic Capacitor CpWith cross capacitance CxValue preferably reduce, so as to sensitivityIt can increase.Reach this purpose, the first metal Between dielectric layer 111 and the depth of the second metal intermetallic dielectric layer 113 need to increase because capacitance is inversely proportional between two conducting plates Distance.It can be seen from the experiment that the first depth d1 and the second depth d2 should be greater than 3 μm.Because in standard CMOS processing procedure, between metal The thickness of dielectric layer is less than 1 μm, this requirement may need that special deposition process is added in the fabrication process.

Assign the stage finally, when the distribution of charge reaches balance, output voltage Vout(step can be measured S06), because improveing the spine of finger and the position of valley in capacitance type fingerprint sensing unit 100, finally by giving output voltage VoutIt embodies.Output voltage is sequentially translated by each improvement capacitance type fingerprint sensing unit 100, thus corresponding a part of user The fingermark image data (step S07) of fingerprint.

It should be noted that voltage described above is the opposite voltage in different circuit nodes.If charging voltage Vdd's Value be it is positive, second metal layer 112 reset process be discharge into 0V or signal ground connection.In this case, in first voltage V1The second voltage V occurred later2With first voltage V1Form negative scale, first voltage V1To second voltage V2Voltage change It is pressure reduction.Charging voltage VddValue may also become 0V, in this case, the process of reseting of second metal layer 112 is It is charged to voltage positive value.In this case, in first voltage V1The second voltage V occurred later2With first voltage V1It is formed Positive scale, first voltage V1To second voltage V2Voltage change be boost process.The latter can be operation improvement capacitance type fingerprint The selective alternative solution of sensing unit 100.

Although the present invention is disclosed above with embodiment, however, it is not to limit the invention, any affiliated technology neck Have usually intellectual in domain, without departing from the spirit and scope of the invention, when can make it is a little change and retouch, therefore this Subject to the protection scope of invention claim institute defender attached after view.

Claims (9)

1. a kind of improvement capacitance type fingerprint sensing unit, characterized by comprising:
Substrate framework has at least one the first metal layer and forms charging circuit and operation circuit, fills alternately to receive Piezoelectric voltage, and assign the charge from the charging circuit into the capacitor of the operation circuit and be simultaneously stopped described in reception and fill Piezoelectric voltage;And
Fingerprint sensing framework is arranged on the substrate framework, includes:
First metal intermetallic dielectric layer, has the first depth, and first depth is greater than 3 μm;
Second metal layer is arranged in first metal intermetallic dielectric layer, and forms induction metal plate;
Second metal intermetallic dielectric layer is arranged in the second metal layer and surround the second metal layer, covers the induction Metal plate simultaneously has the second depth, and second depth is greater than 3 μm;
Third metal layer is arranged in second metal intermetallic dielectric layer, passes through the opening shape being located on the induction metal plate Squarely grid, and it is connected to transient voltage suppresser device, for receiving first voltage and second voltage;And
Passivation layer covers the third metal layer;
Wherein, the limit voltage value of the transient voltage suppressing device is triggered than the first voltage and/or the second voltage It is high;The substrate framework assigns the charge from the charging circuit into the capacitor of the fingerprint sensing framework, and stops simultaneously Only receive the charging voltage.
2. improvement capacitance type fingerprint sensing unit according to claim 1, which is characterized in that wherein charging capacitor is arranged In the charging circuit, for storing charge when the charging capacitor receives the charging voltage;
Parasitic capacitance is present in the operation circuit, and cross capacitance is formed in the third metal layer and the induction metal Between plate.
3. improvement capacitance type fingerprint sensing unit according to claim 2, which is characterized in that wherein when finger is described in When passivation layer, signal capacitor is formed in the finger and the third metal interlevel, and finger capacitor be formed in the finger with Between the induction metal plate.
4. improvement capacitance type fingerprint sensing unit according to claim 3, which is characterized in that wherein assign switch setting and exist Between the operation circuit and the charging circuit, for opening and closing the reception of the charging voltage and assigning charge.
5. improvement capacitance type fingerprint sensing unit according to claim 4, which is characterized in that wherein when the second voltage When generation, the charging voltage stop applying and assignment switch is opened, output voltage changes to be obtained from the charging circuit ?.
6. improvement capacitance type fingerprint sensing unit according to claim 5, which is characterized in that the wherein output voltage Are as follows:
Wherein, VoutIt is the value of the output voltage, VddIt is the value of the charging voltage, V1With V2The first voltage respectively with The value of the second voltage, CrIt is the capacitance of the charging capacitor, CpIt is the value of the parasitic capacitance, CfIt is the finger The value of capacitor, CxIt is the value of the cross capacitance.
7. improvement capacitance type fingerprint sensing unit according to claim 6, which is characterized in that wherein discharge switch setting exists In the operation circuit, when the assignment, which switchs, closes, for by the voltage of the operation circuit and the second metal layer It is reset to signal ground connection.
8. a kind of method for obtaining fingerprint using improvement capacitance type fingerprint sensing unit as claimed in claim 7, feature exist In, comprising the steps of:
It closes and assigns switch to disconnect charging circuit and operation circuit;
Apply first voltage to third metal layer, and resets the electricity of operation circuit and second metal layer by unlatching discharge switch Pressure;
Apply charging voltage to charging circuit;
Close the discharge switch and charge switch;
The assignment is opened to switch and provide second voltage to replace first voltage;
Measure output voltage;And
The output voltage from each improvement capacitance type fingerprint sensing unit is translated, thus the fingerprint of corresponding a part of user Fingermark image data.
9. a kind of fingerprint sensor, characterized by comprising:
A plurality of such as described in any item improvement capacitance type fingerprint sensing units of claim 1-7, to form fingerprint sensing array, Wherein, the setting adjacent to each other of the same architecture of the substrate framework or the fingerprint sensing framework is owned in same level The third metal layer of the improvement capacitance type fingerprint sensing unit connect to form metal grill.
CN201510186265.XA 2015-04-20 2015-04-20 The method and fingerprint sensor for improveing capacitance type fingerprint sensing unit, obtaining fingerprint CN106156710B (en)

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CN106156710B true CN106156710B (en) 2019-06-28

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