JP3624165B2 - Electromagnetic wave detection device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electromagnetic wave detection device for electromagnetic waves such as ultraviolet rays, infrared rays, visible light, X-rays, α rays, and γ rays.
[0002]
[Prior art]
An electromagnetic wave detection device that converts electromagnetic waves such as ultraviolet rays, infrared rays, visible light, X-rays, α-rays, and γ-rays directly or indirectly into charges by a semiconductor and reads out the charges is applied to an imaging device or the like.
[0003]
Among these, an electromagnetic wave detection device that converts high-energy electromagnetic waves such as X-rays into visible light, converts the visible light into charges by a semiconductor, and reads out the charges is disclosed in, for example, US Pat. No. 5,811,790, -288184, U.S. Pat. No. 5,856,699, and JP-A 09-260626.
[0004]
Further, as an electromagnetic wave detection device that converts electromagnetic waves such as ultraviolet rays, infrared rays, visible light, X-rays, α rays, γ rays and the like directly into charges by a semiconductor, for example, a device described in US Pat. No. 5,391,881. is there.
[0005]
14A and 14B are a cross-sectional view and a plan view showing a detector having a laminated structure of a single crystal bulk X-ray detector and a single crystal readout IC.
[0006]
14A and 14B, when a high energy electromagnetic wave 108 such as an X-ray is incident, Si, GaAs, CdTe, HgI.₂A charge is generated in the semiconductor substrate 106, and the charge is transferred to the readout circuit 116 of the integrated circuit chips 110a and 110b via the electrode 114, the bump 120, and the electrode 119. The electrodes 134a to 134d and the electrodes 130a to 130d are electrodes for connecting the semiconductor substrate 106 and the integrated circuit chips 110a and 110b.
[0007]
There is also a direct sensor with a protective diode described in US Pat. No. 5,198,673. FIG. 15 is a schematic block diagram of a read / reset circuit for an optical sensor with a scintillator and a protective diode. In FIG. 15, 222a and 222b are scan switches, 210 is a sensor, 212 is a high voltage source, 214 is a storage capacitor, and 240 is an overvoltage protection element (protection diode).
[0008]
[Problems to be solved by the invention]
By the way, in the electromagnetic wave detection device described above, when a circuit configuration is adopted in which the generated charge is stored in the storage capacitor and the stored charge is read, the charge may remain after the charge is read from the storage capacitor. This charge is added at the next accumulation, and becomes an afterimage in the case of a moving image or the like.
[0009]
In addition, if excessive charges are accumulated in the accumulation capacitor, this may leak to the readout circuit side and the like, and a phenomenon similar to blooming in a CCD image sensor may occur. This phenomenon is particularly noticeable when detecting electromagnetic waves with higher energy than visible light such as X-rays.
[0010]
Alternatively, when a transistor for reading out accumulated charges is formed in a bulk using a single crystal wafer, the charges generated unintentionally in the bulk due to high-energy electromagnetic waves adversely affect the transistor and prevent normal operation. Sometimes.
[0011]
An object of the present invention is to provide an electromagnetic wave detection device superior to conventional devices that can detect even high-energy electromagnetic waves satisfactorily.
[0012]
Another object of the present invention is to provide an electromagnetic wave detection device having a large imaging area at a lower cost than before.
[0013]
Furthermore, another object of the present invention is to provide an electromagnetic wave detection device that suppresses afterimages and leakage of electric charges and is unlikely to malfunction even when high-energy electromagnetic waves are incident.
[0014]
[Means for Solving the Problems]
The present invention includes a conversion element that converts incident electromagnetic waves into electric charges,
A storage capacitor for storing the electric charge converted by the conversion element;
A readout thin film transistor for reading out the electric charge accumulated in the storage capacitor;
One end is connected to the storage capacitor and the gateFirst voltageA reset thin film transistor for applying a reset potential to the storage capacitor by applying
In the electromagnetic wave detection device having
Applied to the gate of the reset thin film transistor during the accumulation periodSecond voltageIs applied to the gate of the readout thin film transistor during the accumulation periodThird voltageFrom the aboveFirst voltageIt is characterized by being set to a value close to.
[0015]
The present invention also includes a conversion element that converts incident electromagnetic waves into electric charges;
Provided on an insulating substrate,A storage capacitor for storing the charge converted by the conversion element, and a storage capacitor stored in the storage capacitor;SaidChargeForwardA reading thin film transistor for reading, a reset thin film transistor in which one end is connected to the storage capacitor, an on-voltage is applied to the gate to apply a reset potential to the storage capacitor,A detection device comprising:
In the electromagnetic wave detection device having
Through the reset thin film transistor during the accumulation periodFrom the amount of charge that can be stored in the storage capacitorIt is characterized by releasing an excessive charge.
[0016]
The conversion element is preferably an element that absorbs electromagnetic waves having higher energy than visible light and converts the electromagnetic waves into charges.
[0017]
The reading thin film transistor and the reset thin film transistor preferably include a non-single-crystal semiconductor layer formed over an insulating substrate.
[0018]
The readout thin film transistor and the reset thin film transistor are formed on an insulating substrate,
The conversion element is preferably formed on a substrate different from the insulating substrate, and is electrically connected to the readout thin film transistor and the reset thin film transistor.
[0019]
The conversion element includes a semiconductor substrate that converts electromagnetic waves into electric charges, a common electrode provided on one surface of the semiconductor substrate, and provided on the other surface of the semiconductor substrate, corresponding to a plurality of two-dimensional pixels, A plurality of electrodes formed separately from each other,
A unit cell including the readout thin film transistor and the reset thin film transistor is disposed on an insulating substrate corresponding to each pixel,
Preferably, the semiconductor substrate and the insulating substrate have a laminated structure, and the plurality of electrodes and the unit cells are electrically connected between the substrates.
[0020]
It is preferable that a plurality of the semiconductor substrates are two-dimensionally arranged and stacked on the insulating substrate, and the common electrodes of the semiconductor substrates are short-circuited.
[0021]
It is preferable that a high voltage potential is applied to the common electrode of the conversion element, and a shielding conductor is provided in the vicinity of the common electrode.
[0022]
It is preferable that a driver circuit for driving the read thin film transistor and the reset thin film transistor and a read circuit for reading a signal from the read thin film transistor are provided on the insulating substrate.
[0023]
In the read thin film transistor, it is preferable that a voltage applied to the source and the drain is determined so that a potential difference between the source and the drain of the thin film transistor is at least 1 V or more in an initial state of the read operation.
[0024]
DETAILED DESCRIPTION OF THE INVENTION
With reference to FIGS. 1-6, the electromagnetic wave detection apparatus by embodiment of this invention is demonstrated.
[0025]
FIG. 1 is a circuit configuration diagram of an electromagnetic wave detection device according to an embodiment of the present invention. FIG. 2 is a circuit configuration diagram including an output circuit for reading a signal from one unit cell.
[0026]
1 is a conversion element, 2 is a storage capacitor, 3 is a reset transistor, 4 is a read transistor, 5 is an output line, 6 is a horizontal drive control line, 7 is a reset control line, and 8 is a reset transistor of the output line. 11 is a reset transistor provided as necessary, 12 is a horizontal transfer transistor, 13 is a horizontal scanning circuit, 14 is a reset circuit, 15 is an amplifier, and 16 is an output circuit.
[0027]
A unit cell that is one pixel includes a conversion element 1 that converts incident electromagnetic waves into charges, a storage capacitor 2 that stores signal charges from the conversion element 1, a transistor 4 that reads signals from the storage capacitor 2, and a signal charge. And a resetting transistor 3 for resetting. These unit cells are two-dimensionally arranged in a matrix to form a so-called area image sensor.
[0028]
The horizontal scanning circuit (shift register or the like) 13 selects the transistor 4 of each unit cell for each row, reads a signal from the storage capacitor 2 of each unit cell to the output line 5, and this signal is connected to the output line 5. Are input to the output circuit 16 via the amplifier 15 and output to the output terminal OUT sequentially for each column by the output circuit 16.
[0029]
Each output line 5 is reset to the reference potential VR2 by the output line reset transistor 8. The output circuit 16 includes, for example, a storage capacitor CSH provided for each output line 5 and a transistor 12 that connects the storage capacitor CSH and the common output line, and outputs φH1, φH2,. The signals are sequentially input to the circuit 16 and the transistors 12 are sequentially turned on, and signals are read from the storage capacitors CSH to the output terminals OUT of the common output line and output. A more detailed driving method will be described later.
[0030]
The capacitance C2 is a capacitance generated by the output line 5, and the capacitance value is C2. The capacitance C2 includes a capacitance at a cross portion between the control lines 6 and 7 and the output line 5 in the horizontal direction and a source (or drain) capacitance in the transistor 4. In a large substrate panel, that is, an apparatus with a large imaging area, the capacitance C2 increases, which greatly affects the ratio of signal (S) to noise (H).
[0031]
If the device is made of a single crystal substrate (such as Si), the capacitance of the substrate and wiring is further added. By forming on a substrate having an insulating surface such as a glass plate, even a 20 cm square panel can be reduced to several tens of pF, which is advantageous.
[0032]
When electromagnetic waves are incident on the conversion element 1, when the capacitance value of the conversion element 1 is C0 and the generated charge is Q, the voltage Vs generated in the storage capacitor 2 (capacitance value C1)
Vs = Q / (C1 + C0) (1)
And
If C1 >> C0 (C1 ≧ 10C0), Vs≈Q / C1 is substantially satisfied.
[0033]
Even when reading from the storage capacitor 2 (capacitance value C1) to the capacitor C2 (capacitance value is also C2), the potential read to the capacitor C2 is V_C2= Q / (C1 + C2).
[0034]
Usually C2 >> C1, so V_C2≒ Q / C2.
[0035]
In other words, V_C2/ Vs = C1 / C2, and is read as a voltage corresponding to the capacity ratio of the storage capacitor 2 (capacitance value C1) and the capacitor C2.
[0036]
Therefore, if the capacitance C2 becomes too large, the noise of the readout amplifier becomes dominant, and the SN ratio as a sensor is lowered.
[0037]
As described above, if the insulating substrate is used, the capacitance C2 can be reduced, which is suitable for a large-sized apparatus. A typical structure of a transistor manufactured over an insulating substrate is shown in FIG.
[0038]
FIG. 3A shows a structure of a thin film transistor called a lower gate stagger type. Reference numeral 21 denotes a gate electrode formed of a metal such as aluminum, chromium, or tantalum. Reference numeral 22 denotes a gate insulating film such as silicon nitride, silicon oxide, aluminum oxide, or tantalum oxide. 23 is a semiconductor layer providing a channel made of amorphous silicon, polycrystalline silicon or the like, 24 is an ohmic contact layer made of a high-concentration N-type semiconductor such as amorphous silicon or microcrystalline silicon, and 25 is aluminum, titanium or the like. Source / drain electrodes made of metal.
[0039]
FIG. 3B also shows another example of a structure of a thin film transistor called a lower gate stagger type. A difference from FIG. 3A is that a channel protective layer 26 for protecting the semiconductor layer 24 above the gate electrode 21 is provided. The channel protective layer 26 is made of an insulator such as silicon nitride or silicon oxide that exhibits an etching rate lower than that of the ohmic contact layer 24.
[0040]
FIGS. 3A and 3B are effective configurations when an amorphous material such as hydrogenated amorphous silicon is used as the semiconductor layer.
[0041]
FIG. 3C shows a thin film transistor having a structure called an upper gate coplanar type. The channel 23, a high concentration impurity region 27 serving as a P-type or N-type source / drain, and a low-concentration impurity provided as necessary. This is an effective configuration when a polycrystalline material such as polycrystalline silicon or a single crystal material is used as the semiconductor constituting the region 28. 21 is a gate electrode made of polycrystalline silicon or metal, 22 is a gate insulating film such as silicon oxide, 25 is a source / drain electrode, and 29 is an insulating film such as silicon oxide or silicon nitride.
[0042]
The carrier mobility of a thin film transistor in which a channel region is formed using a non-single crystal semiconductor such as an amorphous semiconductor or a polycrystalline semiconductor is lower than that of a thin film transistor in which a channel region is formed using a single crystal semiconductor. However, non-single-crystal semiconductor thin film transistors are more difficult than non-single-crystal semiconductor thin-film transistors because defects caused by crystal grain boundaries and dangling bonds that cause this cause trapping of electric charges generated unintentionally by incidence on high-energy rays. And the advantage of being hard to malfunction becomes obvious.
[0043]
In the present embodiment, at least the reset switch 3 and the read switch 4 are manufactured using thin film transistors including these. At least the reset switch 3 and the read switch 4 are preferably manufactured by the same film formation process. Furthermore, if necessary, the transistors that constitute the transistor 8, the horizontal scanning circuit 13, the reset circuit 14, the output circuit 16, and the like may be manufactured using thin film transistors.
[0044]
Next, the operation of the transistor 3 composed of the thin film transistor of this embodiment will be described.
[0045]
After the charge is read from the capacitor C2, the charge of Q · C1 / C2 remains in the storage capacitor 2. For example, if the storage capacitor 2 is 1 pF and the capacitor C2 is 40 pF, 2.5% of the charge remains, which is added at the next storage and becomes noise at the next readout. Appear in
[0046]
In this embodiment, the afterimage can be suppressed by resetting the remaining charge by the transistor 3. Further, in the embodiment of the present invention, the transistor 3 can discharge an excessive charge from a predetermined charge amount to be stored in the storage capacitor 2. In this way, the potential range (accumulated charge amount range) of the storage capacitor 2 can be determined.
[0047]
The initial potential immediately after the reset of the storage capacitor 2 gives a sufficient on-voltage to the transistor 3 to turn on the transistor 3 and set it to the reset reference potential VR1. After resetting, charges are accumulated in the capacitor 2 due to the charge Q flowing from the conversion element 1, but if this exceeds a predetermined amount, there is a risk of leaking to the output line 5 via the read transistor 4. In this embodiment, the final point (saturation potential) of the potential of the capacitor 2 generated by the generated charge is determined by the gate voltage applied to the gate of the transistor 3. For example, when the voltage applied to the gate to determine the gate potential VG is the off voltage VB, the final voltage of the capacitor 2 is VB−Vth (Vth is the threshold value of the transistor 3). For example, when VB = Vth, the final voltage of the capacitor 2 is zero, and the voltage range of the capacitor 2 is VR1 to 0V.
[0048]
Thus, in the present embodiment, the transistor 3 also functions as a reset switch and also functions as an element that determines the operation range (dynamic range) of each pixel.
[0049]
FIG. 4A shows an n-channel thin film transistor circuit, and FIG. 4B shows VG-VS vs. ID characteristics. The Vth in FIG. 4B is set to about 2V.
[0050]
When the gate off voltage VB is -1V, VB-Vth = -3V. The source of the transistor 3 is connected to the storage capacitor 2, and the reference voltage VR1 is applied to the drain.
[0051]
In this state, when the conversion element 1 is irradiated with electromagnetic waves and the generated carrier electrons (-Q) are stored in the storage capacitor 2, the potential becomes VS = -Q / C1. The gate-source voltage of the transistor 3 changes from VG−VS = VB + (Q / C1) according to the accumulated carriers.
When {VB + (Q / C1)} ≧ Vth, a current flows through the drain, and the source voltage VS does not increase any more.
[0052]
Under the above condition, −Q / C1 = − (Vth−VB) = − (2 + 1) V = −3V, which is not −3V or less.
[0053]
When the potential of the storage capacitor 2 is not controlled as described above, the potential of the storage capacitor 2 greatly decreases. For example, when the storage capacitor 2 becomes −20 V or more, the voltage between the gate and the source increases in the transistor of the read transistor 4. Thus, leakage between the gate and the source of the transistor 4 occurs, or the insulating film is broken when the voltage is higher than that.
[0054]
Further, when the source and drain voltage of the transistor 4 becomes a certain voltage (˜20V) or more, the current between the source and the drain is applied to the gate of the transistor 4 even when the off voltage for completely turning off the transistor 4 is applied. Flows out to the vertical line of the sensor, and a blooming phenomenon called a CCD image sensor occurs.
[0055]
That is, the charge overflows from the storage capacitor 2 through the transistor 4, and the influence of the particularly strongly irradiated portion affects the vertical direction.
[0056]
In the embodiment of the present invention, this phenomenon can be suppressed.
[0057]
The operation timing will be described with reference to FIG. Reset, accumulation, and readout are the basic operations.
[0058]
In FIG. 5, φVR1 represents a voltage applied from the reset circuit 14 to the gate of the resetting transistor 3. For example, the high level on-voltage can be set to + 15V and the low level off-voltage VB can be set to about + 5V.
[0059]
φV denotes a voltage applied from the horizontal scanning circuit 13 to the gate of the reading transistor 4, and for example, the high level on-voltage can be + 15V and the low level off-voltage can be −5V.
[0060]
As can be seen by comparing the off voltage VB of the reset transistor 3 and the off voltage of the read transistor 4, the off voltage VB of the reset transistor 3 is on the on voltage side (here, the off voltage of the read transistor 4). The voltage is close to the positive voltage side. φVR2 is a voltage applied to the gate of the transistor 8 to reset the capacitor C2 of the output line 5 to the reference potential VR2, and φVR3 is a voltage applied to the gate of the transistor 11 to reset the capacitor CSH to the reference potential VR3. Is shown. VC1 indicates the potential of the storage capacitor 2 on the floating terminal side.
[0061]
After resetting the reset transistor 3 by turning on the pulse φV1 at a high level, for example, X-ray irradiation as an electromagnetic wave is performed for a certain period. Then, after the pulses φVR2 and φVR3 are turned on to reset the wiring and the sample and hold, the read transistor 4 is turned on by the pulse φV and a signal based on the charge accumulated in the storage capacitor 2 is read. Thereafter, this operation is repeated. X-rays may be continuous irradiation.
[0062]
S1 to S5 indicate changes in voltage when the intensity of the electromagnetic wave is different. When the intensity of the electromagnetic wave is high and a lot of photogenerated charges are generated, the saturation voltage VSAT is saturated at an early stage as in S1, and the electromagnetic wave When the intensity is slightly low, the photogenerated charge is small, and the saturation time is delayed as in S2. Furthermore, depending on the intensity of the electromagnetic wave, it may not be saturated as in S4 and S5. In this case, the voltage VR1 and the voltage VSAT determine the dynamic range.
[0063]
As can be seen by comparing the low level voltages of ΦVR1 and φV, the gate of the reset transistor 3 during the charge accumulation period is supplied with + 5V instead of a voltage that completely turns off (for example, −5V). If this is the case, it is set between the complete on state and the complete off state. As a result, charge flows more easily through the reset transistor 3 than the read transistor 4, so that even if excessive charge is generated, it is released through the transistor 3.
[0064]
In the above example, the configurations of the reset transistor 3 and the read transistor 4 are substantially the same, and their threshold values are the same (threshold errors of less than 1 V due to variations in the manufacturing process are regarded as the same threshold value). It is effective when designed to. In particular, it is more effective when each transistor is manufactured on the same substrate by the same film formation process.
[0065]
On the other hand, as a modification, there is a method of making the threshold values of the reset transistor 3 and the read transistor 4 different from each other. For example, there is a method in which at least one of the reset transistor 3 and the read transistor 4 is doped with impurities, and the channel dope amounts of the respective transistors 3 and 4 are made different. By adopting this method, the threshold voltage of the gate voltage when the reset transistor 3 is completely turned off is set to, for example, a voltage lower than −5 V, and the threshold voltage of the gate voltage when the read transistor 4 is completely turned off is set, for example. In the case of −5V, even if the gate voltages applied to the gates of the reset transistor 3 and the read transistor 4 are set to the same value (for example, −5V), the read transistor 4 is completely turned off. Since the transistor 3 is not completely turned off, excess charge can be preferentially discharged through the resetting transistor 3.
[0066]
FIG. 6 is a timing chart for explaining the operation of the electromagnetic wave detection device. In this example, X-rays are continuously irradiated.
[0067]
D1, D2,... DN indicate the driving of each row, and for example, D1 indicates each timing relating to the first row. In D1, φVR11 is a reset pulse output from the reset circuit 14, φV1 is a drive pulse output from the horizontal scanning circuit 13 to all the lines in one row, and φH (φH1, φH2,...) Is a scanning circuit (not shown). Is a readout pulse output from the output circuit 16 to the output circuit 16. As a result, the signal is sent from the output terminal OUT to an analog / digital conversion circuit (not shown) via an external output amplifier (not shown) and stored in a memory (not shown).
[0068]
As for D1, the potential of the storage capacitor 2 of one row line is reset by the pulse φRESET1 in the period T2 ′, and the accumulation operation in the period T1 is started. During the period (T1-T2), the light from the X-ray irradiation is X Light is received by the conversion element 1 such as a line sensor cell, and the generated charge is stored in the storage capacitor 2. In this embodiment, since the potential of the storage capacitor 2 is lowered by the generated charge, it can be considered that the charge stored in the storage capacitor 2 is released by the reset operation. The transistor 4 is turned on by the pulse φDRIVE1 in the period T2, and charges are transferred to the capacitors C2 in each column. Then, the potential of the storage capacitor 2 in one row line is reset by the pulse φRESET1 in the period T2, and the storage operation in the next period T1 ″ is started.
[0069]
In parallel with the accumulation operation in the period T1 ″, a signal based on the signal charge accumulated in the period T1 is sequentially output to an A / D conversion circuit (not shown) via the output amplifier by a pulse of φREAD1 from each column. In parallel with the accumulation operation in the period T1 ″, a transfer operation is performed in D2 to the capacitor C2 of each column of signal charges for which the accumulation operation has started in the period T1.
[0070]
In this way, each row is read up to D1, D2,. The time periods T1 ′, T1, and T1 ″ shown in FIG. 6 are the same, the time periods T2 ′ and T2 are the same, and the time periods T3 ′ and T3 are the same.
[0071]
The time period T1 is 33 msec (T1≈ 1/30 sec) when, for example, an image of 30 frames is captured per second. When 500 × 500 conversion elements 1 are arranged in a matrix, reading up to D1,..., D500 is required, T2≈T1 / 500, approximately T2≈66 μsec, T3 = T2 / 500, and T3 is It is about 130 nsec.
[0072]
Within the period T2, signal reading (φDRIVE1) and resetting (φRESET1) are performed by the transistor 4. Here, in particular, if the signal is not read sufficiently, the output of the sensor is reduced. The time constant tread = C1RONR is determined by the on-resistance RONR of the storage capacitor 2 and the reading transistor 4, and 3read or more is desired for sufficient reading. The same time is desired for φRESET. Similarly, the time constant of the reset circuit
It is represented by treset = C1RONReset.
Therefore, T2 ≧ 3C1 (RONR + RONReset) is desired.
[0073]
Here, for example, if T2 = 66 μsec,
C1 (RonR + RONReset) ≦ 22 μsec
It becomes. Also, if it is 5tread or more,
C1 (RonR + RONReset) ≦ 13 μsec
It is. RonR and RONReset are desired to be sufficiently small.
[0074]
FIG. 7 is a characteristic diagram showing an example of on-resistance of a thin film transistor using amorphous silicon. The structure of the thin film transistor using amorphous silicon may be considered as a structure as shown in FIGS. The horizontal axis represents the ratio (W / L) between the channel width W and the channel length L of the TFT, and the vertical axis represents the on-resistance value. In FIG. 7, the broken line indicates a calculated value in the case where the thickness of the non-doped hydrogenated amorphous silicon layer (i layer) as the semiconductor layer is 300 nm, and the solid line indicates a calculated value in the case where the thickness is 100 nm. , ▲, ●, △ indicate actual measurement values.
[0075]
The capacitance value C1 is usually several pF. Each time constant can be easily reduced to 10 μsec or less by designing the thin film transistor.
[0076]
However, the on-resistance of the thin film transistor is dependent on the potential difference between the source and drain Vd.
[0077]
FIG. 8 is a characteristic diagram showing the Vd dependence of a sample with an i layer thickness of 500 nm and a sample with the same thickness of 300 nm. When Vd becomes smaller than 1V, the on-resistance rapidly increases. Therefore, when the potential difference between the source and drain is 1 V or more, the time constant can be improved.
[0078]
When C1 << C2, the potential of the capacitor 2 is approximately between VR1 / C2 and (VB−Vth) / C2. For both VR1 / C2 and (VB−Vth) / C2, the voltage Vd between the source and drain of the transistor 4 serving as a switch is set to be 1 V or more.
[0079]
By setting VR2 to at least | VB−Vth | + 1 ≦ | VR2 | V, high-speed reading can be performed through the transistor 4 for all operating conditions.
[0080]
FIG. 9 is a circuit configuration diagram of one pixel of an electromagnetic wave detection device according to another embodiment of the present invention. The configuration described above is different in that the transistor 9 is provided between the conversion element 1 and the capacitor 2, and other configurations can be the same as the configuration described above. The outline of the operation is as follows.
[0081]
First, the conversion element 1 that has received an electromagnetic wave with the transistor 9 turned off accumulates electric charges.
[0082]
The transistor 2 is turned on and the capacitor 2 is reset. Immediately after this, the transistor 4 may be turned on to read so-called reset noise to the output line 5 side. The reset noise may be read out immediately after reading out the optical signal charge described later.
[0083]
After a predetermined time has elapsed from the start of accumulation of photogenerated charges in the conversion element with the transistor 9 turned off, an on pulse φT is applied to the gate of the transistor 9 to turn on the transistor 9 and transfer the charge to the capacitor 2. At this time, excessive charge exceeding the saturation charge amount of the capacitor 2 predetermined by the circuit design (not necessarily the absolute saturation amount that can be stored in the capacitor 2) is supplied to the reset reference power supply side that provides the reset potential through the transistor 2. Released.
[0084]
After the transistor 9 is turned off, the transistor 4 is turned on to read the optical signal charge to the output line 5 side. If the difference between the signal read here and the previous reset noise is taken, a signal with reduced noise can be obtained.
[0085]
FIG. 10 is a schematic cross-sectional view showing an example of the electromagnetic wave detection device according to the present invention.
[0086]
Reference numeral 30 denotes a detection device, which includes an insulating substrate 32 having an array of thin film transistors 33. At least the transistors 3 and 4 described above are formed of such thin film transistors.
[0087]
A conversion element 31 includes a semiconductor substrate 40 for receiving electromagnetic waves, a common electrode 41, individual electrodes 39, and an insulating film 42. The conversion element can generate electrons and holes from incident X-rays and the like, and accumulate one carrier.
[0088]
The thin film transistor 33 includes a gate electrode 43, a channel 44, a source / drain region 45, and a source / drain electrode 46. Reference numeral 34 denotes an interlayer insulating film, and 35 denotes a connection electrode.
[0089]
The conversion element 31 and the detection device 30 are electrically and mechanically connected and fixed by metal layers 36 and 38 serving as connection pads and bumps 37. The connection form is not limited to this.
[0090]
The semiconductor substrate 40 is composed of, for example, a semi-insulating GaAs single crystal substrate, and is configured such that radiation such as X-rays enters through a common electrode 41 such as an AuGeNi alloy that is in ohmic contact with the substrate 40. In this example, radiation is converted into electric charge in a semi-insulating substrate instead of a pn junction. The ohmic contact AuGeNi alloy electrode 39 corresponding to each pixel is electrically connected to the capacitor 2 and the reset transistor 3 and the read transistor 4 constituted by the thin film transistor 33. Will be accumulated.
[0091]
FIG. 11 is a schematic cross-sectional view showing another example of the electromagnetic wave detection device according to the present invention. The difference from the configuration of FIG. 10 is that the conversion element is a PIN junction diode. Specifically, n made of a semiconductor whose main component is GaAs, GaP, Ge, Si, CdTe or the like.⁺Layer 47, i layer 40, p⁺Layer 48 constitutes a diode. The depletion layer extends over the entire i layer 40, and charges are easily collected.
[0092]
FIG. 12 shows the appearance of the X-ray detection apparatus of the present invention, FIG. 12 (a) shows a plan view, and FIG. 12 (b) shows a cross section.
[0093]
In FIG. 12, a plurality of the conversion elements 31 described above are arranged in a two-dimensional matrix on a common detection device 30 in which reset thin film transistors and readout thin film transistors are formed on an insulating substrate such as glass. ing. Each conversion element 31 and the detection device 30 are connected by a bump 37.
[0094]
The signal processing circuit includes a plurality of signal processing circuit chips 50 packaged in a tape carrier that processes signals from a predetermined number of output lines 5, and a common printed wiring board 52 that connects them. The signal processing circuit chip 50 includes the amplifier 15, the output circuit 16, the transistor 8, and the like described above.
[0095]
Similarly, the driver circuit includes a plurality of driver circuit chips 51 in a tape carrier package that drives a predetermined number of drive control lines 6 and 7 and a common printed wiring board 53 that connects them. The driver circuit chip 51 includes a scanning circuit 13 and a reset circuit 14.
[0096]
Chips 50 and 51 are monolithic integrated circuit chips in which transistors are formed in a single crystal semiconductor substrate.
[0097]
When a polycrystalline semiconductor thin film transistor or a single crystal semiconductor thin film transistor is adopted as the thin film transistor, all or part of the signal processing circuit and the driver circuit are formed on the substrate 32 on the CMOS type thin film made of the polycrystalline thin film transistor or the single crystal semiconductor thin film transistor. It may be constituted by an integrated circuit and may be integrated on the substrate 32 together with a plurality of unit cells. By doing so, the number of connection terminals to the outside of the substrate 32 is reduced, and the mounting becomes easy.
[0098]
Reference numeral 54 denotes a one-plate conductor for short-circuiting and commonly biasing the plurality of conversion elements 31. The conductor 54 is in the form of a sheet here, but may be a mesh or the like. 55 is an insulating sheet, and 56 is a sheet for shielding the biasing conductor 54. Since a high voltage of 100 V or more is applied to the conductor 54, the sheet 56 acts as a protection. In particular, in medical applications and the like, it is desired to provide the sheet 56 so that a conductor to which a high voltage is applied is not disposed on the human body side.
[0099]
The insulating sheet 55 is not necessarily provided between the conductor 54 and the sheet 56, and an air gap may be used. In that case, a shield 54 is disposed between the housing of the detection device.
[0100]
In the apparatus shown in FIG. 14, the upper substrate and the lower substrate are single crystal substrates, and a plurality of substrates are used on both the upper and lower sides. Therefore, the wiring is complicated and the enlargement is difficult. It is easy to increase the size of the device.
[0101]
Furthermore, in the apparatus shown in FIG. 14, the upper substrate and the lower substrate have a multi-layered wiring, which is complicated to manufacture, has many processes, and has a poor yield in manufacturing. In addition, the stray capacitance increases as the wiring, the detection speed becomes slow, and the electrical gain falls. On the other hand, since the thin film transistor formed on the insulating substrate is used in the apparatus of the above-described embodiment, such a point is improved.
[0102]
According to the electromagnetic wave detection device of the present embodiment described above,
(1) An afterimage can be eliminated by the reset thin film transistor.
(2) The saturation voltage VS of the storage capacitor 2 can be set by the difference VB−Vth between the OFF voltage of the reset thin film transistor and the threshold voltage, and even when an excessive input is input, the charge leaks to the output line. Can be prevented.
(3) Since the substrate serving as the conversion element can be two-dimensionally arranged and a common large-plate insulating substrate detection device can be stacked on the substrate, it is easy to increase the size of the imaging device.
(4) Even when an amorphous semiconductor thin film transistor, which is said to have low carrier mobility, is used, moving images can be taken well. Of course, high-sensitivity still images with a wide dynamic range can be easily captured.
(5) By setting the potential difference between the source and drain of the readout thin film transistor to at least 1 V or more by setting the reset potential, the response becomes faster.
(6) Since high sensitivity and a wide dynamic range can be obtained, it can be applied not only to medical use but also to analyzers and non-destructive inspection devices for living organisms and non-living organisms.
(7) Since a thin film transistor is used, the establishment of malfunction due to unintentionally generated charges due to high energy rays is low.
[0103]
FIG. 13 is a schematic view showing an example of a medical diagnostic instrument using the electromagnetic wave detection device of the present invention. In FIG. 13, reference numeral 1001 denotes an X-ray tube as an X generation source, 1002 denotes an X-ray shutter for controlling opening / closing of X-ray passage, 1003 denotes an irradiation tube or movable diaphragm, 1004 denotes a subject, and 1005 denotes an electromagnetic wave detection device of the present invention. A radiation detector 1006 is a data processing device for processing data from a signal from the radiation detector 1005. Reference numeral 1007 denotes a computer, which displays an X-ray image or the like on a display 1009 such as a CRT based on a signal from the data processing device 1006, a camera controller 1010, an X-ray controller 1011 or a capacitor-type high voltage generator 1012. The amount of X-ray generation is controlled by controlling the X-ray tube 1001 via the.
[0104]
High energy rays such as X-rays generate an amount of charge generated because the amount of energy incident on the conversion element is extremely different between radiation that has passed through the subject and radiation that has passed through the air without passing through the subject. The difference is extremely large. Therefore, the accumulated charge amount tends to be saturated in the background portion due to the difference between the generated charge amount in the subject image and the background. In the present invention, since excessive charges are discharged through the thin film transistor, deterioration of image quality due to such excessive charges can be better prevented. In addition, since a thin film transistor is used, even if a high energy beam is incident on the thin film transistor portion, a malfunction due to the high energy beam hardly occurs. Furthermore, it is easy to increase the area of the detection device.
[0105]
【The invention's effect】
According to the present invention, afterimages and leakage of charges are suppressed, and even if high-energy electromagnetic waves are incident, malfunctions are unlikely to occur. Therefore, even high-energy electromagnetic waves can be detected well, which is superior to conventional devices. An electromagnetic wave detection device can be provided. Furthermore, an electromagnetic wave detection device having a large imaging area can be provided at a lower cost than before.
[Brief description of the drawings]
FIG. 1 is a circuit configuration diagram of an electromagnetic wave detection device according to an embodiment of the present invention.
FIG. 2 is a circuit configuration diagram of one pixel of the electromagnetic wave detection device according to the embodiment of the present invention.
FIG. 3 is a schematic cross-sectional view showing a configuration of a thin film transistor used in the present invention.
FIG. 4 is a diagram showing a circuit and characteristics of a thin film transistor used in the present invention.
FIG. 5 is a diagram showing a basic drive timing chart of the electromagnetic wave detection device according to the embodiment of the present invention.
FIG. 6 is a diagram illustrating a drive timing chart of the electromagnetic wave detection device according to the embodiment of the present invention.
FIG. 7 is a graph showing on-resistance characteristics of a thin film transistor used in the present invention.
FIG. 8 is a graph showing Vd dependence of on-resistance of a thin film transistor used in the present invention.
FIG. 9 is a circuit configuration diagram of one pixel of an electromagnetic wave detection device according to another embodiment of the present invention.
FIG. 10 is a schematic cross-sectional view of an electromagnetic wave detection device according to an embodiment of the present invention.
FIG. 11 is a schematic cross-sectional view of an electromagnetic wave detection device according to another embodiment of the present invention.
FIG. 12 is a schematic view showing an upper surface and a cross section of an electromagnetic wave detection device according to an embodiment of the present invention.
FIG. 13 is a schematic diagram showing an example of a medical diagnostic instrument using the electromagnetic wave detection device of the present invention as an imaging device.
FIGS. 14A and 14B are a cross-sectional view and a plan view showing a detector having a stacked structure of a single crystal bulk X-ray detector and a single crystal readout IC.
FIG. 15 is a circuit configuration diagram of a read / reset circuit of a direct sensor with a protective diode.
[Explanation of symbols]
1 Conversion element
2 storage capacity
3 Reset transistor
4 Reading transistor
5 output lines
6 Horizontal drive control line
7 Reset control line
8 Output line reset transistor
11 Reset transistor
12 Horizontal transfer transistors
13 Horizontal scanning circuit
14 Reset circuit
15 amplifier
16 Output circuit

Claims (19)

A conversion element that converts incident electromagnetic waves into electric charges;
A storage capacitor for storing the electric charge converted by the conversion element;
A readout thin film transistor for reading out the electric charge accumulated in the storage capacitor;
A reset thin film transistor, one end of which is connected to the storage capacitor and a first voltage is applied to the gate to apply a reset potential to the storage capacitor;
In the electromagnetic wave detection device having
The second voltage applied to the gate of the reset thin film transistor during the accumulation period is set to a value closer to the first voltage than the third voltage applied to the gate of the read thin film transistor during the accumulation period. An electromagnetic wave detection device characterized by that. The electromagnetic wave detection device according to claim 1, wherein the conversion element is an element that absorbs electromagnetic waves having higher energy than visible light and converts the electromagnetic waves into electric charges. The electromagnetic wave detection device according to claim 1, wherein the readout thin film transistor and the reset thin film transistor include a non-single-crystal semiconductor layer formed on an insulating substrate. The readout thin film transistor and the reset thin film transistor are formed on an insulating substrate,
The electromagnetic wave detection device according to claim 1, wherein the conversion element is formed on a substrate different from the insulating substrate and is electrically connected to the readout thin film transistor and the reset thin film transistor. The conversion element includes a semiconductor substrate that converts electromagnetic waves into electric charges, a common electrode provided on one surface of the semiconductor substrate, and provided on the other surface of the semiconductor substrate, corresponding to a plurality of two-dimensional pixels, A plurality of electrodes formed separately from each other,
A unit cell including the readout thin film transistor and the reset thin film transistor is disposed on an insulating substrate corresponding to each pixel,
The electromagnetic wave detection apparatus according to claim 1, wherein the semiconductor substrate and the insulating substrate have a laminated structure, and the plurality of electrodes and the unit cells are electrically connected between the substrates. The electromagnetic wave detection device according to claim 5, wherein a plurality of the semiconductor substrates are two-dimensionally arranged and stacked on the insulating substrate to short-circuit the common electrodes of the semiconductor substrates. The electromagnetic wave detection device according to claim 5, wherein a conductor for shielding is provided in the vicinity of the common electrode while applying a bias potential to the common electrode of the conversion element. 6. The electromagnetic wave detection device according to claim 4, wherein a driver circuit that drives the readout thin film transistor and the reset thin film transistor and a readout circuit that reads a signal from the readout thin film transistor are provided on the insulating substrate. A conversion element that converts incident electromagnetic waves into electric charges;
It provided on an insulating substrate, and a storage capacitor for storing the converted electric charge in the conversion element, and the reading TFT for reading and transferring the accumulated electric charge in the storage capacitor, to one end of the storage capacitor A reset thin film transistor connected to and applied with an on-voltage to the gate to provide a reset potential to the storage capacitor ;
In the electromagnetic wave detection device having
An electromagnetic wave detecting device, wherein during the accumulation period, an excessive charge is discharged through the reset thin film transistor than the amount of charge that can be accumulated in the storage capacitor . The electromagnetic wave detection device according to claim 9, wherein the conversion element is an element that absorbs electromagnetic waves having higher energy than visible light and converts the electromagnetic waves into electric charges. The electromagnetic wave detection device according to claim 9, wherein the readout thin film transistor and the reset thin film transistor include a non-single-crystal semiconductor layer formed on an insulating substrate. The readout thin film transistor and the reset thin film transistor are formed on an insulating substrate,
The electromagnetic wave detection device according to claim 9, wherein the conversion element is formed on a substrate different from the insulating substrate, and is electrically connected to the readout thin film transistor and the reset thin film transistor. The conversion element includes a semiconductor substrate that converts electromagnetic waves into electric charges, a common electrode provided on one surface of the semiconductor substrate, and provided on the other surface of the semiconductor substrate, corresponding to a plurality of two-dimensional pixels, A plurality of electrodes formed separately from each other,
A unit cell including the readout thin film transistor and the reset thin film transistor is disposed on an insulating substrate corresponding to each pixel,
The electromagnetic wave detection device according to claim 9, wherein the semiconductor substrate and the insulating substrate have a laminated structure, and the plurality of electrodes and the unit cells are electrically connected between the substrates. The electromagnetic wave detection device according to claim 13, wherein a plurality of the semiconductor substrates are two-dimensionally arranged and stacked on the insulating substrate to short-circuit the common electrodes of the semiconductor substrates. The electromagnetic wave detection device according to claim 13, wherein a conductor for applying a bias potential to the common electrode of the conversion element and shielding the common electrode is provided near the common electrode. 14. The electromagnetic wave detection device according to claim 12, wherein a driver circuit that drives the readout thin film transistor and the reset thin film transistor and a readout circuit that reads a signal from the readout thin film transistor are provided on the insulating substrate. 10. The electromagnetic wave detection device according to claim 1, wherein the readout thin film transistor determines a voltage applied to the source and drain so that a potential difference between the source and drain of the thin film transistor is at least 1 V or more in an initial state of a readout operation. . The electromagnetic wave detection device according to claim 1, wherein a threshold value of the readout thin film transistor is the same as a threshold value of the reset transistor. The electromagnetic wave detection device according to claim 9, wherein a threshold value of the readout thin film transistor is higher than a threshold value of the reset transistor.

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