CN102637715B - Image sensor - Google Patents

Abstract

The invention relates to the technical field of semiconductors and discloses an image sensor. According to the image sensor, a reflection structure is arranged below a sensitization structure, and under the condition that a depletion layer is not thick enough, incident light is reflected on the bottom of the depletion layer, and the transmission optical distance of the incident light in the depletion layer is increased, thereby ensuring the response speed of a component and improving quantum efficiency. As the superficial area of the reflection structure is larger than the superficial area of the sensitization structure, the incident light can be better reflected, and the quantum efficiency is improved; and by virtue of the selection on proper dielectric materials, dielectric thickness, periods and other parameters, the incident light in a specific wavelength range can be reflected with relatively high efficiency and even are totally reflected.

Description

Imageing sensor

Technical field

The present invention relates to technical field of semiconductors, particularly a kind of imageing sensor with catoptric arrangement.

Background technology

As everyone knows, imageing sensor is a kind of semiconductor device that optical imagery can be converted to the signal of telecommunication.Imageing sensor can be divided into charge coupled cell (Charge-Coupled Device substantially, be called for short " CCD ") and complementary metal oxide semiconductors (CMOS) (Complementary Metal OxideSemiconductor is called for short " CMOS ") imageing sensor.

According to its playback mode, existing cmos image sensor roughly can be divided into passive type element sensor (Passive Pixel Sensor, be called for short " PPS "), active element sensor (ActivePixel Sensor, be called for short " APS ") and digital pixel transducer (Digital Pixel Sensor is called for short " DPS ") three types.

In photoelectric conversion process, after semiconductor is irradiated by light, if the energy of photon equals energy gap, namely hv equals Eg(wherein, and h is planck constant, and v is the frequency of light), then semiconductor is understood absorb photons and produces electron-hole pair; If hv is greater than Eg, then except producing except electron-hole pair, unnecessary energy (hv-Eg) will fall apart consumption in the form of heat; If hv is less than Eg, then when only there is the energy state caused by chemical impurity or physical imperfection in forbidden band, photon just can be absorbed.

Suppose that semiconductor is greater than Eg by a photon energy hv and photon flux is Ф ₀the light source irradiation of (in units of the every cubic centimetre per second number of photons had), when this photon flux enters semiconductor, the absorbed ratio of photon is directly proportional to the intensity of flux, therefore in a distance of increment Δ x, absorbed photon number is α Ф (x) Δ x, wherein α is proportionality constant, is absorption coefficient.

Sensor devices conventional in cmos image sensor is photodiode, for PN junction photodiode, it is the PN junction or the Metals-semiconductor contacts that work in reverse biased substantially, when light signal is beaten on the photodiode, the electron-hole pair produced by light can be separated by depletion region, therefore just has electric current to flow to external circuit.In prior art, in cmos image sensors, photosensitive structure is generally PN junction light sensitive diode, and its opto-electronic conversion completes at depletion layer, and in order to work in high frequency, depletion region must be thinning as much as possible to reduce the transit time; On the other hand, in order to increase quantum efficiency, depletion layer is sufficiently thick, is all absorbed to make most of incident light.Therefore, between response speed and quantum efficiency, produce technical contradiction, must obtain and accept or reject to some extent.Fig. 1 is the structural representation of imageing sensor in prior art, wherein shown in 1 is the PN junction depletion layer realizing opto-electronic conversion, shown in 2 is PN junction photodiode (Photo Diode, be called for short " PD "), shown in 3 is for floating diffusion region (Floating Diffusion, be called for short " FD ") that photogenerated charge stores in 4T type pixel readout circuit.

Summary of the invention

The object of the present invention is to provide a kind of imageing sensor, thus while guarantee response device speed, quantum efficiency can be improved.

For solving the problems of the technologies described above, embodiments of the present invention disclose a kind of imageing sensor, comprising photosensitive structure incident light being changed into the signal of telecommunication, a catoptric arrangement is there is, for by incident from this photosensitive structure front and the light penetrating this photosensitive structure is reflected back this photosensitive structure at the back side of photosensitive structure.

Compared with prior art, the main distinction and effect thereof are embodiment of the present invention:

In the below of photosensitive structure, be provided with a catoptric arrangement, when depletion layer (light absorbing zone of photosensitive region) is thick not, the reflection to incident light is realized bottom depletion layer, increase the light path that incident light transmits in depletion layer, thus while guarantee response device speed, quantum efficiency can be improved.

Further, the surface area of catoptric arrangement is more than or equal to the surface area of photosensitive structure, can realize the reflection to incident light better, improves quantum efficiency.

Further, by selecting the parameters such as suitable dielectric material, dielectric thickness and cycle, the reflection even total reflection effect incident light in particular range of wavelengths being played to greater efficiency can be realized.

Accompanying drawing explanation

Fig. 1 is the structural representation of a kind of imageing sensor in prior art;

Fig. 2 is the structural representation of a kind of imageing sensor in first embodiment of the invention;

Fig. 3 is the structural representation of the catoptric arrangement of a kind of imageing sensor in first embodiment of the invention;

Fig. 4 is a kind of structural representation of pixel readout circuit of 3T type structure;

Fig. 5 is a kind of structural representation of pixel readout circuit of 4T type structure;

Fig. 6 is the transmission spectrum schematic diagram of the catoptric arrangement of a kind of imageing sensor in first embodiment of the invention;

Fig. 7 is the structural representation of the catoptric arrangement of a kind of imageing sensor in second embodiment of the invention;

Fig. 8 is the structural representation of the catoptric arrangement of a kind of imageing sensor in third embodiment of the invention.

Embodiment

In the following description, many ins and outs are proposed in order to make reader understand the application better.But, persons of ordinary skill in the art may appreciate that even without these ins and outs with based on the many variations of following execution mode and amendment, also can realize each claim of the application technical scheme required for protection.

For making the object, technical solutions and advantages of the present invention clearly, below in conjunction with accompanying drawing, embodiments of the present invention are described in further detail.

First embodiment of the invention relates to a kind of imageing sensor.Fig. 2 is the structural representation of this imageing sensor.

Specifically, as shown in Figure 2, this imageing sensor comprises the photosensitive structure 2 incident light being changed into the signal of telecommunication, there is a catoptric arrangement 4 at the back side of photosensitive structure 2, for by incident from this photosensitive structure 2 front and the light penetrating this photosensitive structure 2 is reflected back this photosensitive structure 2.

As can be seen from the figure, photosensitive structure 2 is placed in the surface of this catoptric arrangement 4.Further, the surface area of catoptric arrangement 4 is more than or equal to the surface area of photosensitive structure 2.

The surface area of catoptric arrangement 4 is more than or equal to the surface area of photosensitive structure 2, can realize the reflection to incident light better, improves quantum efficiency.

In fig. 2, shown in 1 is depletion layer, and shown in 3 is floating diffusion region FD.

In the present embodiment, photosensitive structure 2 is photodiode (Photo Diode is called for short " PD "), such as, can be PN junction light sensitive diode, PIN intrinsic semiconductor diode or Metals-semiconductor contacts photodiode etc.Preferably, photosensitive structure 2 is PN junction light sensitive diode, and now, in Fig. 2,1 depletion layer (that is: the light absorbing zone of photosensitive structure 2) being depicted as PN junction, can realize the absorption to incident light in this region, produces photogenerated charge.

In some other execution mode of the present invention, photosensitive structure 2 also can be photoelectricity door.Photoelectricity door, also known as optical gate (photogate).

Catoptric arrangement 4 comprises first medium material and second medium material replaces the periodic stack structure formed, and wherein, first medium material is different with the dielectric constant of second medium material.

The cycle of periodic stack structure is more than or equal to 2, and preferably, the cycle is more than or equal to 4, more excellent, and the cycle equals 10.

First medium material and second medium material have different refractive indexes, are respectively n1, n2, and each first medium layer thickness is d1, and each second medium layer thickness is d2, d1 and d2 can be equal, also can not wait.

Fig. 3 is the structural representation of the catoptric arrangement of A and B two media periodic arrangement.Wherein, A represents first medium material, and thickness is d1; B represents second medium material, and thickness is d2.

Adopt ABAB... alternative stacked as catoptric arrangement 4, can by selecting suitable dielectric material and the reflection of thickness of dielectric layers realization to different wavelength range incident light, make catoptric arrangement 4 pairs of incident lights have high reverse--bias efficiency, even can realize total reflection to the incident light in single wavelength or particular range of wavelengths.

In the below of photosensitive structure 2, be provided with a catoptric arrangement 4, at depletion layer 1(namely: the light absorbing zone of photosensitive structure 2) thick not, the reflection to incident light is realized bottom depletion layer 1, increase the light path that incident light transmits in depletion layer 1, thus while guarantee response device speed, quantum efficiency can be improved.

In addition, Semiconductor substrate and the pixel readout circuit being formed at semiconductor substrate surface is also comprised in this imageing sensor.

Semiconductor substrate can be silicon, germanium, germanium silicon, strained silicon or with any one in the silicon of insulating buried layer, germanium, germanium silicon, strained silicon.Photosensitive structure 2 and catoptric arrangement 4 are all formed at this semiconductor substrate surface, and catoptric arrangement 4 is positioned at the below of photosensitive structure 2.

Pixel readout circuit can be 3T, 4T or 5T structure etc.

According to the number of the transistor that a pixel readout circuit comprises, existing cmos image sensor is divided into 3T type structure and 4T type structure, can also have 5T type structure.

Fig. 4 is a kind of equivalent circuit structure figure of pixel readout circuit of cmos image sensor of existing 3T type structure, comprise: a photodiode 10, for carrying out opto-electronic conversion when exposing, convert the light signal received to the signal of telecommunication, described photodiode 10 comprises p type island region and N-type region, described p type island region ground connection.

A reset transistor M1, for resetting to described photodiode 10 before exposure, resetting is controlled by reset signal Reset signal.In the diagram, described reset transistor M1 selects a N-type Metal-oxide-semicondutor (N Metal-Oxide-Semiconductor is called for short " NMOS ") pipe, and the source electrode of described reset transistor M1 is connected with the N-type region of described photodiode 10; The drain electrode of described reset transistor M1 meets power supply Vdd, and described power supply Vdd is a positive supply.When described reset signal Reset is high level, the N-type region of described photodiode 10 is also connected to power supply Vdd by described reset transistor M1 conducting, under the effect of described power supply Vdd, make described photodiode 10 reverse-biased and the electric charge of whole accumulations of described photodiode 10 can be removed, realizing resetting.Described reset transistor M1 also can be connected by multiple NMOS tube and be formed, or is formed by multiple NMOS tube parallel connection, also can replace described NMOS tube by PMOS.

An amplifier transistor M2, is also one source pole follower, amplifies for the signal of telecommunication produced by described photodiode 10.In the diagram, described amplifier transistor M2 selects a NMOS tube, the grid of described amplifier transistor M2 connects the N-type region of described photodiode 10, and the drain electrode of described amplifier transistor M2 meets described power supply Vdd, and the source electrode of described amplifier transistor M2 is the output of amplifying signal.Described amplifier transistor M2 also can be connected by multiple NMOS tube and be formed or formed by multiple NMOS tube parallel connection.

A row selecting transistor M3, exports for the amplifying signal exported by the source electrode of described amplifier transistor M2.In the diagram, described row selecting transistor M3 selects a NMOS tube, the grid of described row selecting transistor M3 meets row selection signal Rs, and the source electrode of described row selecting transistor M3 connects the source electrode of described amplifier transistor M2, and the drain electrode of described row selecting transistor M3 is output.

Fig. 5 is a kind of equivalent circuit structure figure of pixel readout circuit of cmos image sensor of existing 4T type structure.Compared to 3T type structure, the pixel reading circuit structure figure of the cmos image sensor of existing 4T type structure adds a transfering transistor M4, and described transfering transistor M4 is used for the signal of telecommunication that described photodiode 10 produces to be input to described sense node N1.In Figure 5, described transfering transistor M4 selects a NMOS tube, the grid of described transfering transistor M4 switches through shifting signal TX, the source electrode of described transfering transistor M4 connects the N-type region of described photodiode 10, and the drain electrode of described transfering transistor M4 meets the source electrode of described reset transistor M1 and described sense node N1.

According to optical transmission matrix method, for TE ripple, the eigenmatrix of single-layer medium is:

$M_i=\left[\begin{array}{cc}\cos \left(k_0\mathrm{nd}\cos \mathrm{\θ}\right)& -\frac{i}{\mathrm{\η}}\sin \left(k_0\mathrm{nd}\cos \mathrm{\θ}\right)\\ -\mathrm{i\η}\sin \left(k_0\mathrm{nd}\cos \mathrm{\θ}\right)& \cos \left(k_0\mathrm{nd}\cos \mathrm{\θ}\right)\end{array}\right]$

Wherein, k ₀for the wave number in vacuum, d is the thickness of medium, ε is dielectric constant, and μ is magnetic permeability, and n is the refractive index of medium, and θ is the angle that incident direction and dielectric surface are formed.

The eigenmatrix of multilayer dielectricity is:

$M=\underset{i=1}{\overset{N}{\mathrm{\Π}}}{M}_i=\left[\begin{array}{cc}{T}_{11}& T_{12}\\ T_{21}& T_{22}\end{array}\right],$ Transmissivity $T={\left|t\right|}^2={\left|\frac{{2\mathrm{\η}}_0}{T_{11}{\mathrm{\η}}_0+T_{12}{\mathrm{\η}}_0{\mathrm{\η}}_{N+1}+T_{21}+T_{22}{\mathrm{\η}}_{N+1}}\right|}^2,$ η ₀, η _n+1for effective optical admittance of the upper and lower media of both sides of laminated construction.Can obtain thus, the transmission spectrum of selected media material, dielectric thickness and cycle isoparametric catoptric arrangement 4, thus the reflection even total reflection effect incident light of particular range of wavelengths being played to greater efficiency.

As a preferred embodiment, first medium materials A is Ag, and second medium material B is MgF ₂, n1=0.18, d1=10nm, n2=1.378, d2=110nm, cycle T=4(namely: laminated construction comprises 4 layers of Ag layer alternately and 4 layers of MgF ₂layer), now, blue light, ruddiness transmitance lower (lower than 20%), for the incident light of blue light and red range, can realize the reflectivity of more than 80%.Because red light wavelength is longer, the absorption coefficient of light is relatively little, the light path completing opto-electronic conversion needs is longer, therefore, when depletion layer 1 thinner thickness of PN junction light sensitive diode, for the ruddiness that wavelength is longer, the introducing of catoptric arrangement 4, can make incident light about the light path of depletion region 1 doubles, the absorption efficiency of the incident light greatly improved, has higher quantum efficiency.

As another preferred embodiment, first medium materials A is TiO ₂, n1=2.33, second medium material B is SiO ₂, n2=1.45, d1=50nm, d2=120nm, T=8, now, green light rate is almost 0.As shown in Figure 6, now, catoptric arrangement 4 can realize the total reflection to green glow to its transmission spectrum, substantially increases the quantum efficiency of imageing sensor.

Known based on prior art, introduce the electronic state generation localization that unordered meeting makes band edge in the semiconductors, cause Effective band gap broadening, same principle is also applicable to optics.Introduce unordered in periodic multilayer structure, the light of any frequency range due to relevant back reflection can by local, no matter and its incident angle and its whether be in band gap.When introducing unordered in periodic multilayer structure, due to Bragg reflection effect with introduce the unordered and light local that causes, discrete narrow forbidden band may be made to be extended to continuous print forbidden band.By geometric parameter and the degree of disorder of reasonably adjustment structure, high reverse--bias can be there is in very wide wave-length coverage, thus realize the wide wavestrip high reverse--bias of optics.In addition, the two media Refractive Index of Material difference forming this catoptric arrangement 4 is larger, and the energy gap produced is larger, and according to the reflection demand of different-waveband incident light, adjustment dielectric material is selected and respective thickness, cycle parameter.

Second embodiment of the invention relates to a kind of imageing sensor.Fig. 7 is the structural representation of the catoptric arrangement of this imageing sensor.

Second execution mode improves on the basis of the first execution mode, and main improvements are:

The periodic stack structure that more than 2 or 2 first medium materials A and second medium material B alternately formed is comprised at catoptric arrangement 4, wherein, in different periodic stack structures, not etc., the thickness of second medium material B is not etc. yet for the thickness of first medium materials A.

Fig. 7 be A and B two media respectively periodic arrangement form the structural representation of the catoptric arrangement of two periodic stack structures.Wherein, A represents first medium material, and B represents second medium material; In first periodic stack structure, the thickness of A is the thickness of d1, B is d2; In second period laminated construction, the thickness of A is the thickness of d3, B is d4.

Certainly, in some other execution mode of the present invention, Ke Yishi, in different periodic stack structures, the thickness of first medium material is all equal, and the thickness of second medium material is also all equal, so just with the catoptric arrangement 4 shown in Fig. 3.Also can be that, in different periodic stack structures, not etc., the thickness of second medium material is all inequal for the thickness of first medium material, etc.

By selecting the parameters such as suitable dielectric material, dielectric thickness and cycle, the reflection even total reflection effect incident light of particular range of wavelengths being played to greater efficiency can be realized.

Third embodiment of the invention relates to a kind of imageing sensor.Fig. 8 is the structural representation of the catoptric arrangement of this imageing sensor.

3rd execution mode improves on the basis of the first execution mode, and main improvements are:

In catoptric arrangement 4, also comprise the periodic stack structure that the 3rd dielectric material C and the 4th dielectric material D is alternately formed, wherein, the 3rd dielectric material C is different with the dielectric constant of the 4th dielectric material D.

The structural representation of the catoptric arrangement that Fig. 8 is A, B and C, D tetra-kinds of medium periods arrange.

As shown in Figure 8, A represents first medium material, and thickness is that d1, B represent second medium material, and thickness is that d2, C represent the 3rd dielectric material, and thickness is that d3, D represent the 4th dielectric material, and thickness is d4.

In addition, be appreciated that, in some other execution mode of the present invention, catoptric arrangement 4 can also comprise the 5th dielectric material and the 6th dielectric material, the 7th dielectric material and the 8th dielectric material ... the periodic stack structure alternately formed.

Although by referring to some of the preferred embodiment of the invention, to invention has been diagram and describing, but those of ordinary skill in the art should be understood that and can do various change to it in the form and details, and without departing from the spirit and scope of the present invention.

Claims (5)

1. an imageing sensor, comprising photosensitive structure incident light being changed into the signal of telecommunication, it is characterized in that there is a catoptric arrangement at the back side of described photosensitive structure, for by incident from this photosensitive structure front and the light penetrating this photosensitive structure is reflected back this photosensitive structure; Described catoptric arrangement comprises first medium material and second medium material replaces the periodic stack structure formed, wherein, first medium material is different with the dielectric constant of second medium material, the thickness of first medium material and second medium material is not etc., the thickness of each first medium layer formed by described first medium material is identical, and the thickness of each second dielectric layer formed by described second medium material is identical.

2. imageing sensor according to claim 1, is characterized in that, the surface area of described catoptric arrangement is more than or equal to the surface area of described photosensitive structure.

3. imageing sensor according to claim 2, is characterized in that, in described catoptric arrangement, the cycle of periodic stack structure is more than or equal to 4.

4. imageing sensor according to any one of claim 1 to 3, it is characterized in that, in described catoptric arrangement, also comprise the periodic stack structure that the 3rd dielectric material and the 4th dielectric material are alternately formed, wherein, the 3rd dielectric material is different with the dielectric constant of the 4th dielectric material.

5. imageing sensor according to claim 4, is characterized in that, described first medium material is TiO ₂, thickness is 50nm, and second medium material is SiO ₂, thickness is 120nm.