US20080142920A1 - Highly sensitive photo-sensing element and photo-sensing device using the same - Google Patents

Highly sensitive photo-sensing element and photo-sensing device using the same Download PDF

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US20080142920A1
US20080142920A1 US11/956,551 US95655107A US2008142920A1 US 20080142920 A1 US20080142920 A1 US 20080142920A1 US 95655107 A US95655107 A US 95655107A US 2008142920 A1 US2008142920 A1 US 2008142920A1
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electrode
photo
region
sensing element
sensor
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Mitsuharu Tai
Hideo Sato
Mutsuko Hatano
Masayoshi Kinoshita
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Panasonic Liquid Crystal Display Co Ltd
Japan Display Inc
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    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F30/00—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors
    • H10F30/20—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D86/00—Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates
    • H10D86/40—Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates characterised by multiple TFTs
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10D—INORGANIC ELECTRIC SEMICONDUCTOR DEVICES
    • H10D86/00—Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates
    • H10D86/40—Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates characterised by multiple TFTs
    • H10D86/60—Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates characterised by multiple TFTs wherein the TFTs are in active matrices
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F30/00—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors
    • H10F30/20—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors
    • H10F30/21—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors the devices being sensitive to infrared, visible or ultraviolet radiation
    • H10F30/28—Individual radiation-sensitive semiconductor devices in which radiation controls the flow of current through the devices, e.g. photodetectors the devices having potential barriers, e.g. phototransistors the devices being sensitive to infrared, visible or ultraviolet radiation the devices being characterised by field-effect operation, e.g. junction field-effect phototransistors
    • H10F30/282—Insulated-gate field-effect transistors [IGFET], e.g. MISFET [metal-insulator-semiconductor field-effect transistor] phototransistors
    • H—ELECTRICITY
    • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
    • H10F—INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
    • H10F77/00—Constructional details of devices covered by this subclass
    • G—PHYSICS
    • G09—EDUCATION; CRYPTOGRAPHY; DISPLAY; ADVERTISING; SEALS
    • G09G—ARRANGEMENTS OR CIRCUITS FOR CONTROL OF INDICATING DEVICES USING STATIC MEANS TO PRESENT VARIABLE INFORMATION
    • G09G2360/00—Aspects of the architecture of display systems
    • G09G2360/14—Detecting light within display terminals, e.g. using a single or a plurality of photosensors

Definitions

  • the present invention relates to a thin-film photo-sensing element formed on an insulating film substrate and to a photo-sensing device using the same.
  • the invention relates to an optical sensor array such as an X-ray imaging device, a near-infrared light detector for biometrics, etc. and an image display unit integrated with a display panel with touch panel function, ambient light detecting function, and input function using photo-sensor, e.g. low temperature process semiconductor thin-film transistor used in liquid crystal display, organic electroluminescence display, inorganic electroluminescence display, and electro chromic display, and low temperature process photoconductive element or low temperature process photo-diode element.
  • an optical sensor array such as an X-ray imaging device, a near-infrared light detector for biometrics, etc.
  • an image display unit integrated with a display panel with touch panel function, ambient light detecting function, and input function using photo-sensor, e.g. low temperature process semiconductor thin-film transistor used in liquid crystal display, organic
  • X-ray imaging device is now indispensable as a medical treatment device, and there are strong and continuous demands to simplify the operation of the device and to produce it at lower cost.
  • special notice has been given on the means for biometrics to obtain information from finger vein or palm vein, and it is an imminent problem to have a device or a system for reading the information of this type.
  • a sensor array for optical detection in a certain area i.e. the so-called area sensor, for reading these types of information, and this area sensor must be provided at lower cost.
  • a method has been proposed in the Non-Patent Document 1 as given below, according to which an area sensor is prepared by semiconductor forming process (planer process) on an inexpensive insulating substrate typically represented by glass substrate.
  • the photo-sensor is also required on a medium-to-small size display.
  • the medium-to-small size display is applied for display purpose in mobile devices such as handy phone, digital still camera, PDA (personal digital assistant), or display on board. Multiple functions and high performance characteristics are required on these types of devices and systems. Attention is now focused on the photo-sensor as effective means for adding ambient light detecting characteristics (see the Non-Patent Document 2 given below) and touch panel functions.
  • panel cost is low in the medium-to-small size display. This means that the cost is increased for mounting the photo-sensor or the sensor driver. Therefore, when a pixel circuit is prepared on a glass substrate by semiconductor forming process (planer process), special notice is now given on the technique to prepare the photo-sensor or the sensor driver and on the method to manufacture them at lower cost.
  • the important issues in the groups of products as described above are to prepare a photo-sensing element or a sensor driver on an inexpensive insulating substrate.
  • the sensor driver typically comprises LSI, and it usually requires MOS transistor deposited on monocrystalline silicon wafer or a switching element with high performance characteristics of similar type. To solve such problems, the technique as described below seems to be essential.
  • the thin-film transistor (hereinafter referred as “polycrystalline semiconductor TFT”) has been developed, which is made up by polycrystalline semiconductor. Compared with other types of driver circuit elements, the polycrystalline semiconductor TFT is advantageous in that it has higher driving ability. Peripheral driver circuit can be prepared on the same glass substrate as pixel. As a result, this is convenient for attaining the customization of circuit specification and low cost production by simultaneously performing pixel designing and preparation process and for achieving high reliability by avoiding mechanical fragility of the connections of the driving LSIs and pixels.
  • the polycrystalline semiconductor TFT for liquid crystal display is prepared on a glass substrate for the purpose of reducing the manufacturing cost.
  • process temperature is determined by heat-resistant temperature of the glass.
  • ELA method excimer laser annealing method
  • the polycrystalline semiconductor TFT obtained by this method has driving ability more than 100 times as high as that of TFT (with the channel made of amorphous semiconductor) as used in the conventional type liquid crystal display, and some of the circuits such as driver circuit can be mounted on the glass substrate.
  • the photo-sensor a method to use the polycrystalline semiconductor TFT and a method to use a PIN type diode in addition to pixel circuit and driver circuit are described in the Patent Document 1 as given below.
  • the characteristics required for the photo-sensor are high sensitivity and low noise. If it is limited to the important characteristics of the photo-sensing element, “high sensitivity” means to issue as high signal as possible with respect to a light with certain intensity. This means that a material and an element structure with high light-to-current conversion efficiency are required. “Low noise” means that the signal is as low as possible when the light is not projected.
  • FIG. 12 represents cross-sectional views each showing a conventional type photo-sensing element.
  • FIG. 12 ( a ) shows a PIN type diode element of vertical structure using amorphous silicon layer as a photoelectric conversion layer 113 .
  • FIG. 12 ( b ) shows a TFT element of lateral structure, which uses amorphous silicon film as the photoelectric conversion layer 113 and in which electric charge flows in parallel to the connected surface. Both of these serve as photo-sensing elements.
  • the photo-sensing element as shown in FIG. 12 ( a ) comprises a photoelectric conversion layer 113 of amorphous silicon film interposed between a first metal electrode layer 111 and a second metal electrode layer 112 , and an impurity induced layer 120 , which is prepared between the photoelectric conversion layer 113 and each of the electrode layers.
  • This photo-sensing element is disposed on an insulating substrate 110 .
  • Each of the electrode layers is connected to an electrode line 114 insulated by an interlayer insulating film 115 and is covered with a passivation film 117 .
  • the photo-sensing element shown in FIG. 12 ( b ) comprises a source electrode 131 , a gate electrode 132 , a drain electrode 133 and a photoelectric conversion layer 113 made of amorphous silicon film. Further, it comprises an impurity induced layer 120 disposed on boundary surface between the photoelectric conversion layer 113 and each of the electrodes.
  • This photo-sensing element is mounted on the insulating substrate 110 and is covered with a passivation film 117 .
  • a silicon type material such as silicon, silicon-germanium, etc. should be used because due consideration must be given on environmental problem or process coordination when driver circuit (or pixel circuit) is formed at the same time.
  • driver circuit or pixel circuit
  • the silicon type material among the light components absorbed in the wavelength range from infrared light to visible light, almost all of the light components are converted to electric current. This means that a material having higher absorption coefficient is suitable as the material for the photo-sensing element.
  • phase status solid phase status of semiconductor such as amorphous, crystalline or polycrystalline semiconductor
  • absorption coefficient of the amorphous material is at the highest for the entire wavelength range and this has high resistance.
  • amorphous material is advantageous and suitable as the material of the sensor element.
  • the performance characteristics of the switching element are not sufficient, and it is not possible to have the driver circuit at the same time.
  • TFT is made of amorphous silicon material, which is optimal as the material for the sensor element
  • field effect mobility is 1 cm 2 /Vs or lower.
  • high sensor characteristics can be attained by preparing the sensor array as the structure shown in FIG. 12 , while switching characteristics can be provided by mounting the driver LSI and by connecting via the means such as FPC.
  • the driver circuit (and also, pixel circuit) and the sensor element can be prepared at the same time on the same insulating substrate.
  • TFT with high quality can be obtained, which can be used for the driver circuit.
  • the former is lower in sensitivity than the latter but has higher sensitivity among the sensor elements made of polycrystalline film.
  • intrinsic region I region
  • P region and N region must be separately provided, and this means that the number of photo-masks and the number of processes are increased. This results in higher manufacturing cost compared with other types of sensor elements.
  • TFT As another type of sensor element prepared by using polycrystalline semiconductor film, TFT is known. Because the structure is the same as that of the switching element, which makes up the circuit, it is advantageous in that the number of processes can be decreased and the manufacturing cost can be reduced. However, there are problems in the maintenance and the improvement of sensitivity of the element. Normally, in the channel region, which serves as photoelectric conversion region, thin impurity layer is introduced for the control of threshold voltage. As a result, the depletion region is short, and service life of the electron-hole pair is shortened. Accordingly, the photocurrent to be detected is low, and the sensitivity is worsened. Also, when the gate is positioned closer to the photoelectric conversion surface with respect to the channel, the sensitivity is reduced further due to the light shielding effect of the gate.
  • the sensor driver circuit (and pixel circuit and other circuits if necessary) and a photo-sensing element are manufactured by using polycrystalline silicon film or polycrystalline silicon-germanium film.
  • a diode with a gate using TFT is prepared as the photo-sensing element, and an impurity layer closer to intrinsic layer (the density of activated impurities is 10 17 cm ⁇ 3 or lower) is provided on both sides or on one side of the gate. In so doing, it is possible to maintain or reduce the number of masking processes and the number of photolithographic processes.
  • a low-cost area sensor integrated with driver or an image display unit integrated with photo-sensing element can be provided by maintaining the manufacturing cost of the driver itself and the manufacturing cost of the pixel circuit of the image display unit on a low level.
  • an area sensor with sensor driver circuit (and pixel circuit and other circuits if necessary) and a photo-sensing element with high performance characteristics prepared on inexpensive insulating substrate. Also, it is possible to provide an image display unit integrated with the photo-sensing element.
  • the integration or the incorporation of the photo-sensing element is very useful from the viewpoint of the wide scope of functions, which can be added by its use.
  • the area sensor, in which the photo-sensing element is provided in array is essential and useful in the applications such as devices for medical treatment or for biometrics. In this sense, it is important to manufacture these components at lower cost.
  • photo-sensing element with high performance characteristics and sensor processing circuit can be prepared on inexpensive glass substrate and the products with high reliability can be manufactured at lower cost.
  • FIG. 1 represents conceptual drawings, each showing a photo-sensing element according to the present invention
  • FIG. 2 represents cross-sectional drawings, each showing a photo-sensing element of the prior art and a photo-sensing element according to the present invention respectively;
  • FIG. 3 is a diagram showing the relation between output current and illuminance of the photo-sensing element of the prior art and that of the present invention respectively;
  • FIG. 4 is a cross-sectional view of a switching element manufactured at the same time as the photo-sensing element of the present invention
  • FIG. 5 represents cross-sectional views, each showing another structural example of the photo-sensing element of the present invention.
  • FIG. 6 ( a ) represents drawings, each showing manufacturing process of the photo-sensing element and the switching element;
  • FIG. 6 ( b ) represents drawings, each showing manufacturing process of the photo-sensing element and the switching element;
  • FIG. 6 ( c ) represents drawings, each showing manufacturing process of the photo-sensing element and the switching element;
  • FIG. 7 is a cross-sectional view of the photo-sensing element and the switching element (P-type TFT and N-type TFT);
  • FIG. 8 represents a layout drawing, a cross-sectional view and an equivalent circuit diagram of one pixel of an area sensor
  • FIG. 9 represents a layout drawing, a cross-sectional view and an equivalent circuit diagram of one pixel of another area sensor
  • FIG. 10 represents equivalent circuit diagrams, each for one pixel of another area sensor
  • FIG. 11 represents a rear view, a side view and a front view of an image display unit with the photo-sensing element integrated in it;
  • FIG. 12 represents cross-sectional views, each showing a conventional type photo-sensing element.
  • FIG. 1 represents conceptual drawings, each showing a photo-sensing element according to the present invention.
  • FIG. 1 ( a ) is a cross-sectional view of a photo-sensing element prepared on an insulating substrate
  • FIG. 1 ( b ) is a top view of the photo-sensing element.
  • a first electrode 11 and a second electrode 12 are disposed on a first semiconductor layer on an insulating substrate 10 by introducing highly-doped impurities.
  • a photoelectric conversion region 14 prepared by introducing an intrinsic layer or highly-doped impurities on the first semiconductor layer is disposed between the first and the second electrodes.
  • a third electrode 13 is arranged via an interlayer insulating film 17 .
  • an interconnect 18 On and above the interlayer insulating film 17 , an interconnect 18 , an interlayer insulating film 19 and a passivation film connected with the first electrode 11 and the second electrode 12 via a contact hole 21 are provided respectively.
  • a layer between the first electrode 11 and the second electrode 12 is a layer where an intrinsic layer or very lowly-doped impurities (with the density of majority carriers in the semiconductor layer being 1 ⁇ 10 17 /cm 3 or lower under the conditions with no light projected and with no voltage applied) are introduced, and this layer fulfills the function as a photoelectric conversion layer.
  • the functions as electrodes are given to the first electrode 11 and the second electrode 12 by introducing highly-doped impurities (the density of majority carriers in the semiconductor layer being 1 ⁇ 10 19 /cm 3 under the conditions with no light projected and with no voltage applied).
  • FIG. 2 a photo-sensing element using a conventional type switching TFT as shown in FIG. 2 ( a ) is compared with a photo-sensing element according to the present invention as shown in FIG. 2 ( b ).
  • a depletion region 25 is formed on high voltage side (on the second electrode side in FIG. 2 ), and an electron-hole pair provided primarily on the depletion layer 25 . Therefore, when a light to be detected is projected to the region of the depletion layer 25 , considerable effect can be given on the sensitivity of the sensor.
  • a moderately-doped impurity layer 26 is provided between the first electrode 11 and the second electrode 12 on the first semiconductor layer by introducing the impurities of the same type as the first electrode 11 and the second electrode 12 (with the density of majority carriers being in the range from 1 ⁇ 10 17 /cm 3 to 1 ⁇ 10 19 /cm 3 ).
  • the depletion layer 25 is disposed below the third electrode 13 , and the light coming from above cannot be absorbed when the third electrode 13 is non-transparent to the light to be detected (i.e. when the third electrode 13 does not allow the light to pass).
  • the depletion layer 25 is not covered by the third electrode 13 because it has no moderately-doped impurity layer. Also, in the photo-sensor of the present invention, leakage occurs rarely when the light is not projected because of the photoelectric conversion layer 14 . As a result, the sensitivity is increased more in the photo-sensing element of the present invention compared with the conventional type TFT.
  • FIG. 3 is a diagram to show the relation between output current of photo-sensing elements (i.e. the output of photo-sensing element using the conventional type TFT and the output current of the photo-sensor of the present invention) and illuminance.
  • Each of these photo-sensing elements outputs electric current with a value to match the illuminance.
  • the output current when external light of 100 lx is projected is increased by 43% compared with the photo-sensing element using the conventional type TFT, and that leakage current (noise) when the light is not projected is decreased by 67%.
  • This length is a distance from a line obtained by projecting the end of the third electrode 14 on the first semiconductor layer to each of the first electrode 11 and the second electrode 12 respectively. These are the lengths each shown by arrows in FIG. 1 ( a ). This length can be maintained to a length of 1 ⁇ 2 to 1/10 of the scale of the element.
  • each of the length of the region 15 in contact with the first electrode 11 and the length of the region 16 in contact with the second electrode 12 is 1 ⁇ m or more.
  • FIG. 4 is a cross-sectional view of a switching element (poly-crystalline silicon TFT) prepared at the same time as the photo-sensor of the present invention.
  • a first electrode (source or drain) 41 of a plurality of switching elements 40 in a photo-sensor driver 50 an active layer region (channel) 44 immediately below a third electrode (gate) 43 , a second electrode (drain or source) 42 , and the first electrode 11 , the second electrode 12 and the third electrode 13 , and photoelectric conversion layer 14 of a photo-sensing element 60 are made of polycrystalline silicon film (a first semiconductor film). Because these are made of common material, the manufacturing process can be simplified.
  • the high-performance switching element 40 by using the polycrystalline silicon TFT, and the high-performance photo-sensing element 60 according to the present invention can be prepared on the same insulating substrate 10 through common manufacturing process.
  • the regions 15 and 16 which come into contact with the first electrode 11 and the second electrode 12 of the photo-sensing element 60 respectively. are intrinsic layer or very lowly-doped impurity induced layer (the density of majority carriers in the semiconductor layer under the conditions with no light projected or with no voltage applied being 1 ⁇ 10 17 /cm 3 or lower).
  • the regions 45 and 46 of the first electrode 41 and the second electrode 42 of the switching element 40 are moderately-doped impurity induced layer of the same type as the first electrode 41 and the second electrode 42 of the photo-sensing element 60 (the density of majority carriers under the conditions with no voltage applied being in the range from 1 ⁇ 10 17 /cm 3 to 1 ⁇ 10 19 /cm 3 ).
  • FIGS. 5 ( a ) and ( b ) each represents a cross-sectional view of another structural example of the photo-sensing element of the present invention.
  • the first electrode 11 and the second electrode 12 are prepared on the first semiconductor layer by introducing highly-doped impurities, and a photoelectric conversion region 14 prepared by introducing intrinsic layer or lowly-doped impurities to the first semiconductor layer is disposed between the first electrode and the second electrode.
  • a third electrode 13 is arranged above the photoelectric conversion region 14 via an interlayer insulating film 17 except a region 16 , which comes into contact with the second electrode 12 in the photoelectric conversion region 14 .
  • the region 15 in contact with the first electrode 11 and the region 16 in contact with the photoelectric conversion region 14 and the second electrode 12 are made of the same intrinsic layer or the same very lowly-doped impurity induced layer.
  • the region 15 in contact with the first electrode 11 is a moderately-doped impurity induced layer (the density of majority carriers under the conditions with no light projected and with no voltage applied being in the range from 1 ⁇ 10 17 /cm 3 to 1 ⁇ 10 19 /cm 3 ).
  • the region 15 in contact with the first electrode 11 is a moderately-doped impurity induced layer (the density of majority carriers under the conditions with no light projected and with no voltage applied being in the range from 1 ⁇ 10 17 /cm 3 to 1 ⁇ 10 19 /cm 3 ).
  • the region 15 in contact with the first electrode 11 is a highly-doped impurity induced layer (the density of majority carriers in the semiconductor layer under the conditions with no light projected and with no voltage applied being 1 ⁇ 10 19 /cm 3 or more).
  • the sensitivity of the sensor can be maintained.
  • highly sensitive photo-sensing element can be provided even in the structure as shown in FIG. 5 similarly to the first electrode 11 and the second electrode 12 . Because resistance between the electrodes is decreased, this is an effective structure in case the photo-sensing element also serves as the switching element.
  • an insulating substrate 10 is prepared.
  • an example is given on an inexpensive glass substrate used as the insulating substrate 10
  • a plastic substrate typically represented by PET, an expensive quartz substrate or a metal substrate may be used.
  • sodium, boron, etc. are contained in the substrate, and this may cause contamination to the semiconductor layer.
  • an undercoating film such as silicon oxide film or silicon nitride film.
  • an amorphous silicon film or a microcrystalline silicon film 61 is deposited by chemical vapor deposition (CVD). Then, excimer laser 62 is irradiated to the silicon film 61 to turn it to polycrystalline, and a polycrystalline silicon film 63 is prepared.
  • the polycrystalline silicon film 63 is processed by photolithographic process to prepare a polycrystalline silicon film 64 of island-like shape.
  • a gate insulating film 65 made of silicon oxide film is deposited by chemical vapor deposition.
  • the material of the gate insulating film 65 is not limited to silicon oxide film, while it is preferable to select a material having high dielectric constant, high insulating property, low fixed charge, low interface trapped charge, low density of trapping state, and high process coordination.
  • boron is introduced, and a low density boron injection layer (NE layer) 67 is prepared.
  • NE layer low density boron injection layer
  • non-injection region of the photoelectric conversion layer of photo-sensing element is determined by a photo-resist 68 in the photolithographic process so that impurities may not be intermingled.
  • the photoelectric conversion layer is a very thin impurity induced layer, very lowly-doped impurities are introduced in advance.
  • As the methods to introduce the impurities there are: a method to intermingle with impurity gas at the time of deposition, a method to introduce impurities by ion implantation to the polycrystalline silicon film via the gate insulating film, etc., while there is no limitation on the selection of the method.
  • non-injection regions such as an N-type TFT region 70 , a photo-sensor region 71 , etc. are determined by using a photo-resist 69 in the photolithographic process.
  • a photo-resist 69 By introducing phosphorus through implantation of ions 72 , a lowly-doped phosphorus injection layer (PE layer) 73 is prepared.
  • the purpose of the use of impurities in the PE layer 73 and the NE layer is to adjust threshold value of TFT.
  • the optimal value is in the range from 1 ⁇ 10 11 cm ⁇ 2 to 1 ⁇ 10 13 cm ⁇ 2 .
  • the density of majority carriers in the NE layer 66 and the PE layer 72 is in the range from 1 ⁇ 10 15 to 1 ⁇ 10 17 /cm 3 .
  • the optimal value of boron injection quantity is determined by the threshold value of the N-type TFT, and the optimal value of phosphorus injection quantity is determined by the threshold value of P-type TFT.
  • metal film for gate electrode is deposited by CVD or sputtering.
  • the metal film for gate electrode is processed by using photo-resist in the photolithographic process, and a gate electrode 76 is prepared.
  • the metal film for the gate electrode may not necessarily be a metal film. It may be a polycrystalline silicon film prepared by introducing highly-doped impurities with lower resistance.
  • ions 78 are injected by using photo-resist 77 in the photolithographic process, and phosphorus is introduced to both sides of the gate electrode 76 of TFT, and a moderately-doped phosphorus injection layer (N-layer) 79 is prepared.
  • This introduction of impurities has the purpose to improve the reliability of the N-type TFT.
  • the optimal value to be injected is between 1 ⁇ 10 11 cm ⁇ 2 to 1 ⁇ 10 15 cm ⁇ 2 .
  • the density of majority carriers in the N-layer 79 will be in the range from 1 ⁇ 10 15 /cm 3 to 1 ⁇ 10 19 /cm 3 .
  • a non-injection region is determined by using a photo-resist 80 in the photolithographic process.
  • phosphorus is introduced, and a highly-doped phosphorus injection layer (N+ layer) 82 is prepared.
  • the dosage of phosphorus in the ion implantation layer is preferably 1 ⁇ 10 15 cm ⁇ 2 or more because it is necessary to sufficiently decrease the resistance of the electrode. In this case, the density of majority carriers in the N+ layer can be 1 ⁇ 10 19 /cm 3 or higher.
  • a non-injection region of the N-type TFT and the photo-sensor are determined by using a mask used in FIG. 6 ( a ) ( 4 ) and by using a photo-resist 83 in the photolithographic process.
  • ions 84 By implanting ions 84 to the electrode region of the P-type TFT, boron is introduced, and a highly-doped boron injection layer (P+ layer) 85 is prepared.
  • the dosage at the time of ion implantation is preferably 1 ⁇ 10 15 cm ⁇ 2 or more because the resistance of the electrode must be sufficiently decreased. In this case, the density of majority carriers in the P+ layer will be 10 19 /cm 3 or more.
  • the photolithographic process can be simplified and the use of photo-masks can be eliminated, while it is disadvantageous in that many defects occur in the active layer of the P-type TFT.
  • an interlayer insulating film 86 is deposited above the gate electrode 76 by CVD using TEOS (tetraethoxy silane) as raw material. Then, annealing is performed for activation of the introduced impurities. Next, a contact hole 88 is prepared on electrode portion by using photo-resist 87 in the photolithographic process. The interlayer insulating film 86 is used to insulate the interconnects as prepared later from the gate electrode of the lower layer and polycrystalline semiconductor layer. In this respect, any type of film may be used so far as it has insulating property.
  • TEOS tetraethoxy silane
  • parasitic capacitance must be reduced, and it is desirable to use a material, which has low specific dielectric constant and low film stress so that it has good process coordination to the thickening of the film. Further, to be compatible with display function, the transparency of the film is important, and it is desirable to use a material, which has high transmittance to the visible light.
  • silicon oxide film using TEOS gas as raw material is used as an example.
  • the materials for interconnects are deposited, and interconnects 80 are prepared by the photolithographic process.
  • a passivation film 90 is prepared by CVD. If necessary, after the passivation film 90 is prepared, additional annealing is performed to improve the characteristics of TFT. Any type of film may be used so far as it has insulating property as in the case of the interlayer insulating film 86 .
  • a flattened insulating film 91 is prepared by using an insulating layer formed with paste method or insulating resistant material. Then, by using a photo-resist 92 in the photolithographic process, a contact hole 93 is formed for the contact between the interconnects 89 and ITO in the subsequent process.
  • a transparent electrode film such as ITO is prepared. Then, using a photo-resist 94 in the photo-lithographic process, a transparent electrode 95 is prepared. Then, a passivation film is prepared on it if necessary, and a contact can be provided in the photolithographic process.
  • FIG. 7 shows an example of a P-type TFT 701 , an N-type TFT 702 and a photo-sensing element 703 as prepared in the present embodiment.
  • a photo-sensing element as shown in FIG. 1 ( a ) is prepared.
  • the TFT to constitute the circuit, and the photo-sensing element of all of the structures shown in FIG. 5 can be prepared at the same time.
  • FIGS. 8 ( a ), ( b ) and ( c ) represent a layout of one pixel of an area sensor using a photo-sensor TFT according to the present invention, its equivalent circuit diagram and an operation timing chart respectively.
  • the voltage of a bias line 801 (a second electrode 812 ) of a photo-sensor TFT 800 is set to a value lower than the voltage of a sensor node 802 (a first electrode 811 of the photo-sensor TFT 800 ), and the voltage of a sensor gate line 803 (a third electrode 813 of the photo-sensor TFT 800 ) is set to a higher value, and voltage of the sensor node 802 (the first electrode 811 ) is reset.
  • the voltage of the bias line 801 (the second electrode 812 ) is set to a value considerably higher than the voltage of the sensor node 802 (the first electrode 811 ), and the voltage of the sensor gate line 803 (the third electrode 813 ) is decreased.
  • the photo-sensor TFT 800 is in “off” state, and only very slight electric current flows to the photo-sensor TFT 800 .
  • more electric current flows than the time when light is not projected, and the voltage of the sensor node (the first electrode 811 ) is increased.
  • Reference numeral 815 in FIG. 8 ( a ) represents a contact hole to connect the data line 805 to the first electrode (or the second electrode) of the switching TFT 820
  • the numeral 816 denotes a contact hole to connect the bias line 801 to the second electrode 812 of the photo-sensor TFT 800 .
  • FIGS. 9 ( a ), ( b ) and ( c ) represent another example of a layout drawing of one pixel of an area sensor using a photo-sensor TFT according to the present invention, its equivalent circuit diagram, and an operation timing chart respectively.
  • the third electrode 813 of the photo-sensor TFT 800 and the first electrode 811 are short-circuited.
  • the voltage of the bias line 801 (the second electrode 812 ) is set to a lower value than the voltage of the sensor node 802 (the first electrode 811 and the third electrode 813 ) before the operation of the sensor, and the voltage on the sensor node 802 is reset.
  • the voltage of the bias line 801 (the second electrode 812 ) is set to a value considerably higher than the voltage on the sensor node 802 .
  • the photo-sensor TFT 800 is in “off” state, and only very slight electric current flows to the photo-sensor TFT 800 .
  • more electric current than that of the time when light is not projected flows, and the voltage on the sensor node 802 is increased.
  • FIG. 10 shows another example of equivalent circuit diagram of one pixel of an area sensor using the photo-sensor TFT according to the present invention.
  • FIG. 10 ( a ) shows that the third electrode 813 of the photo-sensor TFT 800 can be controlled by an independent line.
  • FIG. 10 ( b ) the third electrode 813 of the photo-sensor TFT 800 is short-circuited to the first electrode 811 .
  • the voltage of the bias line 801 (the second electrode 812 ) is set to a value lower than the voltage of the sensor node 802 , and the voltage on the sensor node 802 is reset.
  • the voltage of the bias line 801 (the second electrode 812 ) is set to a value considerably higher than the voltage on the sensor node 802 .
  • the voltage on the data line 805 is set to a value lower than the voltage on the gate line 804 in advance (or it may be set reversely).
  • the switching TFT 820 When the voltage on the sensor node 802 reaches a value higher than the sum of the voltage of the data line 805 (the voltage of the gate line in reverse case) and the threshold value of the switching TFT 820 , the switching TFT 820 is turned to “on” state, and the voltage on the data line 805 reaches. The voltage approximately equal to the voltage on the gate line 804 .
  • the change of the voltage is read by the sensor driver, which is provided outside the region of the area sensor. Therefore, if the switching TFT 820 can be turned on within the operation time of the sensor, signal can be outputted regardless of the illuminance. As a result, by changing the sensor operation time, gray scale can be detected.
  • the sensors applied in FIG. 8 , FIG. 9 and FIG. 10 may be any of the sensors shown in FIG. 1 ( a ) and FIGS. 5 ( a ) and ( b ).
  • FIGS. 5 ( a ) and ( b ) are asymmetrical, and care must be taken on the arrangement of the electrodes.
  • examples of the area sensors are shown. If pixel circuits are arranged for each pixel at the same time as the sensor, an image display unit with photo-sensor functions can be provided. Signal line to send signal to pixel, gate line, etc. may be added newly. Or, the bias line, the data line or the gate line may be used in common by adjusting the timing of signal line.
  • FIG. 11 represents schematical drawings of an image display unit integrated with the photo-sensing element of the present invention.
  • FIG. 11 ( a ) is a rear view of an image display unit.
  • a printed board 103 for driver LSI comprising a driver LSI 102 is disposed.
  • a plurality of pixels formed on the front side of the image display unit are driven.
  • FIG. 11 ( b ) is a side view of the image display unit.
  • a photo-sensor 105 comprising the photo-sensing element of the present invention and a plurality of pixels 106 arranged on an image display region are disposed.
  • FIG. 11 ( c ) is a front view of the image display unit.
  • a peripheral driver circuit 107 for driving pixels 106 On a glass substrate 101 , a peripheral driver circuit 107 for driving pixels 106 , a photo-sensor driver processing circuit 108 for processing the output of the photo-sensor 105 , a backlight, and other control circuits 109 are disposed.
  • sensor signals to correspond to external light from the photo-sensor 105 are processed by the photo-sensor driver processing circuit 108 , and the signals are sent to the peripheral driver circuit 107 , which drives the pixels 106 .
  • image quality such as luminance, contrast, etc. of the image display unit are controlled, depending on the sensor signals.
  • a part of the driver is composed of LSIs and these are mounted on rear surface via FPC.
  • TFT arranged on the glass substrate can be used sequentially. In so doing, LSIs and the cost for mounting them can be reduced, and the decrease of mechanical reliability due to the mounting can be avoided.
  • the driver can be designed at the time of the designing of pixels, and this facilitates the customization of the components.
  • the sensor and its driver can be integrated on the glass substrate, and this makes it possible to arrange and mount the sensor and processing circuits at any desired position in compact arrangement.

Landscapes

  • Solid State Image Pick-Up Elements (AREA)
  • Thin Film Transistor (AREA)
  • Light Receiving Elements (AREA)
  • Liquid Crystal (AREA)
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CN103579267A (zh) * 2012-07-18 2014-02-12 全视科技有限公司 含有具有三角形截面的金属栅格的图像传感器
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KR101675841B1 (ko) * 2009-12-21 2016-11-14 엘지디스플레이 주식회사 표시 장치의 포토 센서 및 이의 제조 방법
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EP2448012A4 (en) * 2009-06-26 2012-11-21 Sharp Kk PHOTOTRANSISTOR AND DISPLAYING EQUIPMENT THUS EQUIPPED
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CN103579267A (zh) * 2012-07-18 2014-02-12 全视科技有限公司 含有具有三角形截面的金属栅格的图像传感器
CN120236553A (zh) * 2025-06-03 2025-07-01 惠科股份有限公司 显示装置及其驱动方法

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KR20080056648A (ko) 2008-06-23
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