CN2574222Y - X-ray image sensor - Google Patents

Abstract

The utility model relates to an x-ray image sensor, which mainly comprises elements of an electrode layer, a converting layer, a gap layer, a charge collecting layer, etc., wherein, a sensor uses the 'x-ray-charge' converting layer to operate a 'x-ray-charge-field emitting electron' mode in an appropriate electric field to make the field emitting electron move to a charge collector made of semiconductor material positioned on the opposite side of the converting layer and deduce an x-ray exposed amount originally entering the 'x-ray-charge' converting layer from a charge amount of a capacitance in the charge collector. The surface of the converting layer material is processed into a rough surface form with convex tips (Tip) with very small radius of curvature; the gap layer is arranged between the converting layer and the charge collector. Therefore, a field emitting layer forms a local region with concentrated fields for the convenience of generating field emissions. Simultaneously, the sensor can be operated under low voltage and provide protective action for the capacitance of the charge collector.

Description

The X-ray image sensor

Technical field

The utility model relates to a kind of X-ray image sensor, specifically utilize an emission mode, field emission electron is shifted to be positioned at the charge-trapping utmost point on an emission layer opposite, inferred the original digital X-ray image sensor that is incident on the X-ray exposed amount of conversion layer with the quantity of electric charge number that moves into the charge-trapping electrode capacitance.

Background technology

The traditional X-ray optical image is that the mode with egative film presents, its mode that obtains image is the light that converts near the wavelength visible light by the X-ray that the flourescent sheet that places unexposed egative film front will penetrate sufferer to, so that the egative film exposure again through the process of developing and fixing, presents the X-ray image.Exposing, transmitting, dashing and send in the process, if wrong generation then must obtain image again.Aspect the preservation of image, all there is defective in the traditional X-ray exograph X in the storage space and the storage safe problem of egative film.

With the X-ray image digitization and be stored in and then can solve above-mentioned storage area and storage safe problem in the digital memory body.Numerical data is easy to carry about with one and the characteristic that transmits also make these image datas have access to and tele-medicine on become quite convenient.If handled, digitized video also can be used to detect disease again.Above-mentioned is the place that the digital X-ray image is better than the traditional X-ray exograph X.

Obtain the modal mode of digital X-ray image at present and X-ray is converted to the signal of light or electricity for using the conversion material, collocation photodiode or charge-trapping device, the X-ray video conversion is become electronic signal output, obtain the digital X-ray image data afterwards by A/D (analog/digital converter) again.The above-mentioned mode that is converted near visible light (or visible light wavelength) principle by X-ray is called non-direct mode (In-direct), and the mode person who is converted to electrical principles by X-ray is called direct-type (Direct).

Above-mentioned direct-type digital X-ray image sensor, as shown in Figure 3, it uses semi-conducting material to be the X-ray conversion layer, as Se or the like material.

Its operation workflow is that conversion layer becomes e with incident X-ray conversion of signals ^--h ⁺Right, under the biased outside effect, there is the electric field e of upper and lower part electrode ^--h ⁺To separation, wherein e ^-Moved toward the bottom electrode, simultaneously below electrode cause one and be equal to the immigration electron charge, these Charge Storage control when above-mentioned electric charge is shifted out electric capacity (being read output signal) by grid (Gate) in the TFT module again in by the electric capacity that TFT constituted, and do the output order of each output unit by outside sequencing control, after ADC output digital image signal.The thickness of above-mentioned conversion layer generally has hundreds of μ m approximately, and the voltage that must be added on upper electrode is about between～kV to 10KV, and the Se material then is the conversion layer material of using always, and these class material more options have generation e ^--h ⁺Semi-conducting material to characteristic.

But; because this type of X-ray image sensor must apply quite high voltage (approximate number kilovolt); apply high voltage like this and mainly be because free electron is quite short and mobility (Mobility) is not high enough in the life-span of Se (Lift Time); therefore make the free electron fast moving to improve its utilance with high electric field; apply so high voltage and make on the sensor production quite difficulty, when also using institute must quite strictness of safeguard measure.

Another kind of non-direct-type digital X-ray image sensor, this type of transducer must not use high voltage operation, but changes into prejudice light after absorbing with scintillator (Scintillator) but with X-ray, comes the sensing visible light with photodiode (Photodiode) again.

But with panel type X-ray image sensor palpus this size (4 " * 4 "～7 " * 7 "), so big photodiode qualification rate on making is quite low and quite complicated, so price is rather stiff.

Summary of the invention

The shortcoming of comprehensive above two kinds of digital X-ray image sensors.In with low voltage operating, the X-ray image sensor that is compatible to the prior art manufacturing will be the approach that improves above-mentioned shortcoming.Therefore, the utility model provides a kind of X-ray image sensor that utilizes an emission mode, consist predominantly of elements such as electrode layer, conversion layer, clearance layer and charge collection layer, wherein this transducer is to utilize " X-ray-electric charge " conversion layer suitably operating " X-ray-electric charge-field emission electron " pattern in the electric field, field emission electron is shifted to be positioned at the conversion layer opposite, and infer the X-ray exposed amount of original being incident in " X-ray-electric charge " conversion layer with the quantity of electric charge number that moves into the charge-trapping electrode capacitance by the made charge-trapping utmost point of semi-conducting material.

A kind of X-ray image sensor, this transducer consists predominantly of elements such as electrode layer, conversion layer, clearance layer and charge collection layer, it is characterized in that: a clearance layer is set between the conversion layer and the charge-trapping utmost point; Apply a suitable electric field according to electrode layer at conversion layer, form an emission mode, make the field emission electron of conversion layer shift to the charge-trapping utmost point that is positioned at the conversion layer opposite.

Described X-ray image sensor is characterized in that described clearance layer is the scope at 50 μ m～1000 μ m.

Described X-ray image sensor is characterized in that the conversion layer material is the material of selecting to have big band gap.

Described X-ray image sensor, it is characterized in that surface adjacent to the conversion layer material of clearance layer forms protrudes and has a so-called rough form at quite little radius of curvature tip.

Described X-ray image sensor is characterized in that rough of described conversion layer is needle-like, sheet or tubulose form.

Described X-ray image sensor is characterized in that described charge collection layer is to make with semi-conducting material.

Described X-ray image sensor is characterized in that the other growth in described conversion layer surface has an emission layer, and the suitable electric field that is applied will make described field emission electron shift to the described charge-trapping utmost point.

Described X-ray image sensor is characterized in that an emissive layer materials is the material that selection has high band gap and high conductivity.

Described X-ray image sensor is characterized in that an emissive layer materials is the composite material of DLC.

Described X-ray image sensor, it is characterized in that surface adjacent to the field emissive layer materials of clearance layer forms protrudes and the so-called coarse surface form at the radius of curvature tip that tool is quite little.

Above-mentioned conversion layer materials processing becomes the surface to present to protrude and the so-called coarse surface form at the radius of curvature tip that tool is quite little; And between the conversion layer and the charge-trapping utmost point, a clearance layer is set.Therefore, will make an emission layer form the zone that local field is concentrated, be beneficial to an emission and take place, the sensor can low voltage operating simultaneously, and provides the protective effect of charge-trapping electrode capacitance.

Brief Description Of Drawings

Fig. 1 is the schematic diagram of the utility model X-ray image sensor;

Fig. 2 is another embodiment of the utility model X-ray image sensor;

Fig. 3 is the schematic diagram of known direct-type digital X-ray image sensor.

Embodiment

Of the present utility model emission X-ray image sensor consists predominantly of electrode layer 1, conversion layer 2, clearance layer 4 and charge collection layer 3, as shown in Figure 1.Described electrode layer 1 is positioned at a side of conversion layer 2, and is formed with a clearance layer 4 between the another side of conversion layer 2 and charge collection layer 3.

This transducer is to utilize " X-ray-electric charge " conversion layer 2 suitably operating " X-ray-electric charge-field emission electron " pattern in the electric field, field emission electron is shifted to be positioned at the charge-trapping utmost point 3 on conversion layer 2 opposites, and infer the X-ray exposed amount of original being incident in " X-ray-electric charge " conversion layer 2 with the quantity of electric charge number that moves into the charge-trapping utmost point 3 electric capacity.

The operation of the utility model X-ray image sensor, at first be on above-mentioned electrode layer 1, to apply a back bias voltage (negative bias), because electrode layer 1 is a good conductor, so bias voltage can be uniformly distributed on the electrode layer 1, promptly conversion layer 2 suffered bias voltages also are uniform.Because conversion layer 2 is high impedance (near a state of insulation) material semiconductor, and thickness is quite thick, so bias voltage will produce pressure drop in conversion layer 2.

When X-ray begins to act on conversion layer 2, in conversion layer 2, will generate many electron-hole pair (e ^--h ⁺Pair), and these electron-hole pairs will move because of the electric field that bias voltage constituted that is added on the electrode layer 1, and this moment, free electron was shifted to conversion layer 2 surfaces of adjacent segment layer 4, and the hole then moves on to electrode layer 1.Because the generation that above-mentioned electronics-hole is right and mobile descends the impedance of conversion layer 1, the pressure drop of conversion layer 2 simultaneously also descends.

Because above-mentioned institute biasing is a fixed value, and the impedance of clearance layer 4 does not change at this moment, and an emission effect will take place on the surface of conversion layer 2 in the therefore pressure drop that is changed.

Above-mentioned emissive porwer (emission current) is then relevant with the free electron number that conversion layer 2 generates or provided, what then relevant with the X-ray intensity of incident (the two are directly proportional) that electronics-hole is right.

The consideration that above-mentioned conversion layer 2 materials are selected, it at first is the conversion efficiency that X-ray is converted to electronics, generally speaking, the conversion efficiency of material with big band gap (bandgap energy) is less, but this also and do not mean that the material with low band-gap just is suitable for using in this purposes, because consider that the energy that ambient temperature provided may be higher than 1.5eV when room temperature is used, it is right promptly to use environment just to be enough to make material to generate electronics-hole, and these electric charges are sources of the assorted signal of background.These electric charges will to generate more electronics-hole right because of colliding other atoms under the effect of extra electric field, and therefore assorted signal will be very big.Adopt the material of higher band gap will more be appropriate to real operating environment; conversion layer 2 materials are converted to the electric charge function except having above-mentioned X-ray; protect the function of rear portion circuit in addition; be that conversion layer 2 absorbs the incident X-ray; reduce the amount that is not absorbed X-ray, penetrate the radiation damage that X-ray is radiated at caused assorted signal of rear portion circuit and material elements to reduce these.

Moreover, the field emission needs very big field, for avoiding under high field action, generating Joule heat, the utility model uses the mode that reduces the regional area radius of curvature, for example the Surface Machining with conversion layer 2 materials becomes tool needle-like (Tip) or sheet (Sheet) or tubulose so-called coarse surface forms such as (nanotube), owing to be present in the electronics of material internal, it is subjected to contiguous nuclear attraction and can't breaks away from nuclear constraint easily and become the electronics (free electron) that can move freely.Generally will obtain free electron and material can be applied suitable electric field, make the energy of electronics bring up to the constraint that is enough to break away from atom, the electronics that so is positioned at material surface might break away from material and become free electron.Electronics has the characteristic of particle and fluctuation, if contiguous atom and electron institute in interatomic energy barrier (Energy Well) very thin thickness, then the wave characteristic of electronics will make electronics bigger probability distribution be arranged beyond energy barrier.This moment, then electronics had an opportunity to break away from atom constraint becoming free electron (the especially electronics of material surface atom) if in time apply an electric field around electronics.The free electron that aforesaid way produces is called field emission electron.In regularly arranged material, contiguous atom formation to the energy barrier of electronics will with apply electric field produce an electric field that emission is required very greatly.The electronics that is positioned at material internal has from the active force existence of contiguous atom from all directions, but it is also less because of the less so suffered constraint of contiguous atom to be positioned at surperficial electronics.Therefore the electronics in the atom on surface more easily becomes field emission electron.From reducing the viewpoint of electronics binding force, the number of contiguous atom is operable mode around the minimizing atom.Observe from the geometry of material surface, though the more inner atom of the atom of flat surfaces bears less binding force, if can further make the surface present the tip (rough face) of protruding and having quite little radius of curvature, for example needle-like, sheet or tubulose form then can obtain than the littler atom of the suffered binding force of flat surfaces atom.So will make this place form the zone that local field is concentrated, take place in order to the field emission.

Moreover, between the conversion layer 2 and the charge-trapping utmost point 3, must there be a clearance layer 4, this clearance layer 4 must have the characteristic that electronics is easy to pass through, and vacuum environment is just conforming with this requirement.Vacuum gap layer 4 has following effect, at first is that vacuum gap layer 4 has been isolated the conversion layer 2 and the charge-trapping utmost point 3, and an emission effect is just taken place thus, that is to say that vacuum gap layer 4 is for one of necessary condition of emission effect takes place.Moreover, vacuum gap layer 4 can be used as electronics obtains energy (kinetic energy) from electric field place, there is an electric field in vacuum gap layer 4 because of the voltage that adds, simultaneously there to be suitable distance to make the electronics that comes because of the field emission accelerate to the kinetic energy state, electronics with kinetic energy will clash into the charge-trapping utmost point 3, if make the electrode material of apparatus characteristic of semiconductor, this bump will make the extra electronics-hole of the charge-trapping utmost point 3 generations right, be equivalent to original electronic signal and be exaggerated.Known direct-type X-ray image sensor often suffers excessive X-ray dosage because of sensing unit (Sensor Area) somewhere, and the phenomenon that the electric capacity of collecting electric charge is punched because of the too high voltage generation electric capacity of the excessive generation of charging.In the utility model X-ray image sensor structure, vacuum gap layer 4 provides and has cushioned above-mentioned electric capacity by the function of high electrical breakdown.Moreover in the X-ray image sensor structure, vacuum gap layer 4 can be considered an electric capacity with the charge-trapping utmost point 3 capacitances in series.Because of saying with respect to indivedual charge-trapping utmost points 3, vacuum gap layer 4 entire area are much bigger, contiguous vacuum gap layer 4 will be led earlier wear phenomenon, too much voltage will be shared by the bigger conversion layer 2 of area (emission layer).In fact, cross multi-charge because of partial charge collector 3 electric capacity and direct into the conversion layer 2 back voltage burdens that conversion layer 2 is caused not quite, therefore can't cause damage conversion layer 2.Therefore vacuum gap layer 4 can provide the 3 electric capacity protective effects of the charge-trapping utmost point.

Above-mentioned clearance layer 4 can make the electronics that leaves material surface because of field emission obtain kinetic energy from electric field, further clashes into the charge-trapping utmost point 3 and produces more electric charge charge signal is strengthened.Therefore when faint X-ray exposed amount, still can obtain enough big charge signal.

3 of the charge-trapping utmost points are for collecting the electronics that come through clearance layer 4 by conversion layer 2 surface emitting, these free electrons after X-ray has shone again the known TFT circuit 6 by back segment read one by one.

With aforementioned known direct-type X-ray image sensor collect the required high voltage that applies of electric charge (～kV) compare the required voltage ratio of emission lower (hundreds of volt) that produces of the utility model.Because of electric field level by applying voltage and two interpolar clearance layer 4 distance is determined, by clearance layer 4 distances of 3 of conversion layer 2 and the charge-trapping utmost points are dwindled, can reduce the required voltage that applies significantly, because the value of an emission with respect to clearance layer 4 and the pass of supplying voltage is:

E＝V/d

(E: an emission value; V: supply voltage; D: the clearance layer width)

That is to say that above-mentioned V value is to be directly proportional with the d value, therefore considering that an E value of emission needs the condition more than 1MV/m, and the applied voltage before not producing an emission all drops under the situation of conversion layer 2, too big voltage will make the voltage-resistent characteristic of conversion layer 2 produce very big test, have may puncture (Breakdown) greatly and damage.

Moreover, though less d value can produce very big field by small voltage, but consider the technological level and the cost factor of processing, when the d value was too small, the surface smoothness of conversion layer 2 will be referred to whether produce the possibility of the contact short circuit (Short) of 3 of the conversion layer 2 and the charge-trapping utmost points when applied voltage.On the other hand, reasonably extra electric field also helps to generate in the conversion layer 2 moving of electron-hole pair, therefore the d value is being considered under the factors such as material behavior, machining accuracy and element running, it is comparatively reasonable that the d value of clearance layer 4 is chosen in the scope of 50 μ m～1000 μ m, that is the applied voltage of required use under this scope is in 50V～1000V scope, and it is low that the really more known direct-type X-ray image sensor of these applied voltage values is collected the required high voltage～kV that applies of electric charge.

The above-mentioned X-ray image sensor that forms according to the field emission mode for the utility model, but be the generation of further strengthening above-mentioned emission mode, another embodiment of the present invention is grown below above-mentioned conversion layer 2 emission layer 5, as shown in Figure 2.

When X-ray begins to act on conversion layer 2, the pressure drop that conversion layer 2 is changed will be reacted on the emission layer 5 on the scene totally, and emission layer 5 suffered pressure drops on the spot increase suddenly.

According to above-mentioned situation, a large amount of free electrons will be poured into an emission layer 5, and drop on the pressure drop increase suddenly again of an emission layer 5, and the surface of emission layer 5 on the scene takes place in an emission effect.

As previously mentioned, the right generation in the electronics one hole pressure drop of conversion layer 2 is descended (be in the conversion layer electric field descend), and the more zone of (promptly be incident in this X-ray more for a long time) the more pressure drop that will descend of electron-hole pair, but still can possess the right ability in mobile electron-hole, promptly the field emission layer 5 under this zone will obtain bigger additional voltage drop, so the field emission effect in this zone will be stronger.Otherwise, will be gentle in electronics-hole to the field emission effect that generates the field emission layer 5 under the less zone, therefore the strong and weak difference of X-ray will widen thus.

As for the selection of field emission layer 5 materials, above-mentioned substance emission (disengaging) free electron (e ^-) the pattern principle be to utilize field (Field) add to become free electron so that the electronics in the material is attracted out, it must high temperature, but will sizable impressed field.Because an emission is not the energy of electronics to be brought up to the program that can overcome free energy barrier produce free electron, but added field make the electron institute can well (Energy Well) between width diminish, utilize tunneling effect (Tumning Effect), send a telegraph son eventually and can pass and produce free electron.

But electron energy (vibration) also will rise when generating free electron with the field, if above-mentioned energy well is not high enough, the possibility that then may take place electronics to cross the energy well and between atom, transmit, unfavorable on the contrary emission effect, and will move caused Joule heat because of electric charge, material temperature is risen, even melt.Therefore field emmision material must have high band gap (Energy gap), as SiC, diamond, Mo, elements such as w or its compound, but for the continuation material that then impedance is too big of maintaining field emission is also improper, because it can't provide free electron to replenish for the free electron after the emission.Therefore the material that has high band gap and high conductivity will be the selection as field emmision material, DLC (Diamond LikeCarbon) composite material that for example has double grading, and this DLC has the Sp3 carbon of high band gap, and the good Sp2 carbon of conductivity.

The configuration of surface of relevant emission layer 5, similarly under high field action, generate Joule heat for avoiding, the surface of this emission layer 5 is to use the mode that reduces the regional area radius of curvature, for example Surface Machining becomes tool needle-like or so-called coarse surface form such as sheet or tubulose, so will make this place form the zone that local field is concentrated, take place in order to the field emission.

As for the clearance layer between above-mentioned the emission layer 5 and the charge-trapping utmost point 3, the d value of this clearance layer is also identical with aforementioned principles to be the scope that is set in 50 μ m～1000 μ m.

Claims (10)

1, a kind of X-ray image sensor, this transducer consists predominantly of elements such as electrode layer, conversion layer, clearance layer and charge collection layer, it is characterized in that:

Between the conversion layer and the charge-trapping utmost point, a clearance layer is set;

Apply a suitable electric field according to electrode layer at conversion layer, form an emission mode, make the field emission electron of conversion layer shift to the charge-trapping utmost point that is positioned at the conversion layer opposite.

2, X-ray image sensor as claimed in claim 1 is characterized in that described clearance layer is the scope at 50 μ m～1000 μ m.

3, X-ray image sensor as claimed in claim 1 is characterized in that the conversion layer material is the material of selecting to have big band gap.

4, X-ray image sensor as claimed in claim 1, it is characterized in that surface adjacent to the conversion layer material of clearance layer forms protrudes and has a so-called rough form at quite little radius of curvature tip.

5, X-ray image sensor as claimed in claim 1 is characterized in that rough of described conversion layer is needle-like, sheet or tubulose form.

6, X-ray image sensor as claimed in claim 1 is characterized in that described charge collection layer is to make with semi-conducting material.

7, X-ray image sensor as claimed in claim 1 is characterized in that the other growth in described conversion layer surface has an emission layer, and the suitable electric field that is applied will make described field emission electron shift to the described charge-trapping utmost point.

8, X-ray image sensor as claimed in claim 7 is characterized in that an emissive layer materials is the material that selection has high band gap and high conductivity.

9, X-ray image sensor as claimed in claim 7 is characterized in that an emissive layer materials is the composite material of DLC.

10, X-ray image sensor as claimed in claim 7, it is characterized in that surface adjacent to the field emissive layer materials of clearance layer forms protrudes and the so-called coarse surface form at the radius of curvature tip that tool is quite little.

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