CA2594737A1 - High sensitivity a-si:h photo-transistor pixel with flicker noise reduction for near infra-red in-vivo bio-molecular imaging - Google Patents
High sensitivity a-si:h photo-transistor pixel with flicker noise reduction for near infra-red in-vivo bio-molecular imaging Download PDFInfo
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- CA2594737A1 CA2594737A1 CA002594737A CA2594737A CA2594737A1 CA 2594737 A1 CA2594737 A1 CA 2594737A1 CA 002594737 A CA002594737 A CA 002594737A CA 2594737 A CA2594737 A CA 2594737A CA 2594737 A1 CA2594737 A1 CA 2594737A1
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- photo
- red
- pixel
- high sensitivity
- noise reduction
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- 238000003384 imaging method Methods 0.000 title description 20
- 230000035945 sensitivity Effects 0.000 title description 6
- 238000001727 in vivo Methods 0.000 title description 2
- 239000010409 thin film Substances 0.000 abstract description 4
- 230000003287 optical effect Effects 0.000 abstract description 2
- 238000001228 spectrum Methods 0.000 abstract description 2
- 238000005516 engineering process Methods 0.000 description 10
- 229910021417 amorphous silicon Inorganic materials 0.000 description 8
- 238000000034 method Methods 0.000 description 8
- 238000010521 absorption reaction Methods 0.000 description 4
- 229910021419 crystalline silicon Inorganic materials 0.000 description 3
- 238000005286 illumination Methods 0.000 description 3
- 230000032683 aging Effects 0.000 description 2
- 230000003321 amplification Effects 0.000 description 2
- 238000003491 array Methods 0.000 description 2
- 230000001413 cellular effect Effects 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 239000011521 glass Substances 0.000 description 2
- 230000010354 integration Effects 0.000 description 2
- 238000005259 measurement Methods 0.000 description 2
- 229910021424 microcrystalline silicon Inorganic materials 0.000 description 2
- 229910021423 nanocrystalline silicon Inorganic materials 0.000 description 2
- 238000003199 nucleic acid amplification method Methods 0.000 description 2
- 210000000056 organ Anatomy 0.000 description 2
- 239000004033 plastic Substances 0.000 description 2
- 239000000758 substrate Substances 0.000 description 2
- 238000004166 bioassay Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000001514 detection method Methods 0.000 description 1
- 230000003292 diminished effect Effects 0.000 description 1
- 239000011888 foil Substances 0.000 description 1
- 239000011159 matrix material Substances 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 238000000386 microscopy Methods 0.000 description 1
- 230000035515 penetration Effects 0.000 description 1
- 238000004611 spectroscopical analysis Methods 0.000 description 1
- 230000035882 stress Effects 0.000 description 1
- 238000002211 ultraviolet spectrum Methods 0.000 description 1
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/70—SSIS architectures; Circuits associated therewith
- H04N25/76—Addressed sensors, e.g. MOS or CMOS sensors
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N25/00—Circuitry of solid-state image sensors [SSIS]; Control thereof
- H04N25/60—Noise processing, e.g. detecting, correcting, reducing or removing noise
- H04N25/63—Noise processing, e.g. detecting, correcting, reducing or removing noise applied to dark current
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
- H04N23/20—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from infrared radiation only
- H04N23/21—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from infrared radiation only from near infrared [NIR] radiation
Landscapes
- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Solid State Image Pick-Up Elements (AREA)
Abstract
Disclosed is a new thin film phototransistor based image sensor with improved responsivity to infra-red and ultra-violet range of the optical spectrum.
Description
FIELD OF THE INVENTION
The present invention generally relates to active matrix sensor arrays for applications ranging from imaging at tissue and organ levels down to molecular and cellular levels.
Specific examples range from large area multi-modal biomedical and other x-ray imaging (when coupled with a scintillation layer) to optical bio-molecular imaging, including that of fluorescence-based bio-assays.
SUMMARY OF INVENTION
Disclosed technique provides high responsivity to infra-red and ultra-violet wavelengths critical for a variety of imaging applications. Because the responsivity to ultra violet is improved, the technique disclosed here also enables extensions of the imaging space to large area UV
sensing and imaging. The noise performance of the pixel is improved by a switch biasing technique.
Although the pixel circuit and architecture disclosed here has been implemented using amorphous silicon technology, it can be extended to crystalline Si (including CMOS) technologies, as well as thin film micro-/nano-crystalline Si and organic technologies on glass and plastic substrates.
ADVANTAGES
This driving scheme provides for low noise, high sensitivity, and low power detection. The technique disclosed here provides an extremely economical solution to imaging as the image sensor and readout technique can be implemented in standard amorphous silicon flat panel technology.
The technology commonly used in a variety of bio-imaging applications is based on the charge coupled device (CCD). While CCD cameras provide for high throughput imaging, they suffer from low collection efficiency (<1%), by virtue of the bulky optics required to image over large areas, and prohibitively high cost. Moreover, substantial cooling is required to reduce the noise associated with the dark current so as to enable reasonably large integration times to boost signal-to-noise ratio. The issues related to cost, size, and performance can be effectively addressed with the amorphous silicon (a-Si:H) flat panel technology, which has emerged as a promising technology for large area pixelated arrays of electronics. For example, a key requirement for in-vivo bio-molecular imaging applications, is the sensitivity of the a-Si:H imager to near infra-red (NIR, 700-900 nm).
This region of the spectrum enables penetration through tissue, to provide more accurate diagnostics.
Sensitivity to UV provides a better choice of better quantum efficiency scintillation layers for x-ray imaging applications, besides direct UV sensing/imaging applications. This invention presents a pixel that shows enhanced responsivity of an a-Si:H thin film transistor (photo-TFT) to the NIR and UV
spectrum by a means of trap-assisted absorption. Moreover, the flicker noise (1/f) of the pixel is reduced by adopting a switched biasing technique similar to what has been reported in crystalline Si transistors. More importantly, because the pixel provides for continuous amplification, the integration time is diminished, solving the problem of background noise stemming from the dark current.
Fig. I shows the structure of an inverted staggered TFT used as a photo-detector. The aspect ratio of the TFT is 800 m/23 m. To reduce the effects of TFT aging on photocurrent (I;lj,,,,,,,a,;oõ -Id,,k), the dark current is extracted before each measurement. As the gate voltage passes the sub-threshold regime, the responsivity to red illumination increases (see Fig. 2). This is most likely due to trap-assisted absorption in which the photons are absorbed by the trapped electrons resulting in a smaller trapping time and consequently larger current. Also, the TFT photo-sensor provides high sensitivity to the ultra violet range.
Fig. 3(a) shows the photocurrent of the TFT as a function of illumination intensity. The sensitivity of photo-TFT increases as the gate voltage increases. More importantly, the photocurrent is significantly high (> 50 nA) even at low intensities which is critical for high dynamic range, high precision imaging.
An example of a bio-molecular pixel circuit/architecture is shown in Fig. 4.
The pixel is designed and operated to deploy trap-assisted absorption in the TFT while lowering the 1/f noise and aging. These are attributes which can be exploited for various other sensing architectures for a variety of other imaging applications. During the reset cycle, the drain-source (VDs) and gate-source (VGs) voltages are zero to reduce electrical stress for increased stability and lifetime [3].
Moreover, the leakage current is zero since VGs and VDs are zero, leading to relatively lower cross talk from adjacent pixels in the same column. During the read cycle, TI and T2 are turned on and off alternatively, providing current to Idata in turn. Fig. 5 shows the array structure of the photo-TFT pixel. Here, a row is selected by applying a pulse to its corresponding VB I and VB2 lines (e.g. VB1[i] and VB2[1]). The output current of each pixel in a selected row is read out by a trans-resistance or charge amplifier.
Fig. 6 shows the photomicrograph of the circuit.
The photocurrent of the pixel for two different illumination conditions is shown in Fig. 7(a). As shown in Fig. 7(b), using switched biasing improves the photocurrent slightly which can be due to the effect of light on the switching operation of the TFT. Also, due to the switched biasing technique, the 1/f noise is reduced. Fig. 8 shows the setup for measuring the noise of the pixel circuit. Results show that the flicker noise is dropped by over 6 dB compared to a single TFT- see Fig. 9 - leading to an overall 7.5 dB improvement in SNR.
Since sensor, readout, and amplification are the same elements, the pixel size can be made relatively small. For example, with state of the art a-Si:H technology with a 3- m channel length, the TFT aspect ratio drops to less than 100 m/3 m reducing the pixel size to 50x50 mZ or smaller areas.
Consequently, the photo-TFT pixel can provide high resolution imaging capability over large area.
The measurement results presented here show that the trap-assisted absorption in the a-Si:H
photo-TFT can be deployed for improving the responsivity to N[R and UV leading to a low cost, large-area solution for imaging. The SNR is significantly improved by virtue of switched- biasing. The pixel architecture example shown here can be easily extended to a variety of other imaging applications, enabling new microscopy and spectroscopy techniques for a wide range of modalities associated with imaging at molecular and cellular levels to imaging at tissue and organ levels. The implementation of the pixel circuit and architecture disclosed here can be extended to crystalline Si (and CMOS) technologies, as well as thin film micro-/nano-crystalline Si and organic technologies on non-conventional substrates including glass, plastic and metal foils.
The present invention generally relates to active matrix sensor arrays for applications ranging from imaging at tissue and organ levels down to molecular and cellular levels.
Specific examples range from large area multi-modal biomedical and other x-ray imaging (when coupled with a scintillation layer) to optical bio-molecular imaging, including that of fluorescence-based bio-assays.
SUMMARY OF INVENTION
Disclosed technique provides high responsivity to infra-red and ultra-violet wavelengths critical for a variety of imaging applications. Because the responsivity to ultra violet is improved, the technique disclosed here also enables extensions of the imaging space to large area UV
sensing and imaging. The noise performance of the pixel is improved by a switch biasing technique.
Although the pixel circuit and architecture disclosed here has been implemented using amorphous silicon technology, it can be extended to crystalline Si (including CMOS) technologies, as well as thin film micro-/nano-crystalline Si and organic technologies on glass and plastic substrates.
ADVANTAGES
This driving scheme provides for low noise, high sensitivity, and low power detection. The technique disclosed here provides an extremely economical solution to imaging as the image sensor and readout technique can be implemented in standard amorphous silicon flat panel technology.
The technology commonly used in a variety of bio-imaging applications is based on the charge coupled device (CCD). While CCD cameras provide for high throughput imaging, they suffer from low collection efficiency (<1%), by virtue of the bulky optics required to image over large areas, and prohibitively high cost. Moreover, substantial cooling is required to reduce the noise associated with the dark current so as to enable reasonably large integration times to boost signal-to-noise ratio. The issues related to cost, size, and performance can be effectively addressed with the amorphous silicon (a-Si:H) flat panel technology, which has emerged as a promising technology for large area pixelated arrays of electronics. For example, a key requirement for in-vivo bio-molecular imaging applications, is the sensitivity of the a-Si:H imager to near infra-red (NIR, 700-900 nm).
This region of the spectrum enables penetration through tissue, to provide more accurate diagnostics.
Sensitivity to UV provides a better choice of better quantum efficiency scintillation layers for x-ray imaging applications, besides direct UV sensing/imaging applications. This invention presents a pixel that shows enhanced responsivity of an a-Si:H thin film transistor (photo-TFT) to the NIR and UV
spectrum by a means of trap-assisted absorption. Moreover, the flicker noise (1/f) of the pixel is reduced by adopting a switched biasing technique similar to what has been reported in crystalline Si transistors. More importantly, because the pixel provides for continuous amplification, the integration time is diminished, solving the problem of background noise stemming from the dark current.
Fig. I shows the structure of an inverted staggered TFT used as a photo-detector. The aspect ratio of the TFT is 800 m/23 m. To reduce the effects of TFT aging on photocurrent (I;lj,,,,,,,a,;oõ -Id,,k), the dark current is extracted before each measurement. As the gate voltage passes the sub-threshold regime, the responsivity to red illumination increases (see Fig. 2). This is most likely due to trap-assisted absorption in which the photons are absorbed by the trapped electrons resulting in a smaller trapping time and consequently larger current. Also, the TFT photo-sensor provides high sensitivity to the ultra violet range.
Fig. 3(a) shows the photocurrent of the TFT as a function of illumination intensity. The sensitivity of photo-TFT increases as the gate voltage increases. More importantly, the photocurrent is significantly high (> 50 nA) even at low intensities which is critical for high dynamic range, high precision imaging.
An example of a bio-molecular pixel circuit/architecture is shown in Fig. 4.
The pixel is designed and operated to deploy trap-assisted absorption in the TFT while lowering the 1/f noise and aging. These are attributes which can be exploited for various other sensing architectures for a variety of other imaging applications. During the reset cycle, the drain-source (VDs) and gate-source (VGs) voltages are zero to reduce electrical stress for increased stability and lifetime [3].
Moreover, the leakage current is zero since VGs and VDs are zero, leading to relatively lower cross talk from adjacent pixels in the same column. During the read cycle, TI and T2 are turned on and off alternatively, providing current to Idata in turn. Fig. 5 shows the array structure of the photo-TFT pixel. Here, a row is selected by applying a pulse to its corresponding VB I and VB2 lines (e.g. VB1[i] and VB2[1]). The output current of each pixel in a selected row is read out by a trans-resistance or charge amplifier.
Fig. 6 shows the photomicrograph of the circuit.
The photocurrent of the pixel for two different illumination conditions is shown in Fig. 7(a). As shown in Fig. 7(b), using switched biasing improves the photocurrent slightly which can be due to the effect of light on the switching operation of the TFT. Also, due to the switched biasing technique, the 1/f noise is reduced. Fig. 8 shows the setup for measuring the noise of the pixel circuit. Results show that the flicker noise is dropped by over 6 dB compared to a single TFT- see Fig. 9 - leading to an overall 7.5 dB improvement in SNR.
Since sensor, readout, and amplification are the same elements, the pixel size can be made relatively small. For example, with state of the art a-Si:H technology with a 3- m channel length, the TFT aspect ratio drops to less than 100 m/3 m reducing the pixel size to 50x50 mZ or smaller areas.
Consequently, the photo-TFT pixel can provide high resolution imaging capability over large area.
The measurement results presented here show that the trap-assisted absorption in the a-Si:H
photo-TFT can be deployed for improving the responsivity to N[R and UV leading to a low cost, large-area solution for imaging. The SNR is significantly improved by virtue of switched- biasing. The pixel architecture example shown here can be easily extended to a variety of other imaging applications, enabling new microscopy and spectroscopy techniques for a wide range of modalities associated with imaging at molecular and cellular levels to imaging at tissue and organ levels. The implementation of the pixel circuit and architecture disclosed here can be extended to crystalline Si (and CMOS) technologies, as well as thin film micro-/nano-crystalline Si and organic technologies on non-conventional substrates including glass, plastic and metal foils.
Claims
Priority Applications (8)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002594737A CA2594737A1 (en) | 2007-07-13 | 2007-07-13 | High sensitivity a-si:h photo-transistor pixel with flicker noise reduction for near infra-red in-vivo bio-molecular imaging |
| CA 2680043 CA2680043A1 (en) | 2007-03-05 | 2007-12-17 | Sensor pixels, arrays and array systems and methods therefor |
| US12/530,151 US8487231B2 (en) | 2007-03-05 | 2007-12-17 | Sensor pixels, arrays and array systems and methods therefor |
| PCT/CA2007/002238 WO2008106764A1 (en) | 2007-03-05 | 2007-12-17 | Sensor pixels, arrays and array systems and methods therefor |
| EP20070855520 EP2126526A1 (en) | 2007-03-05 | 2007-12-17 | Sensor pixels, arrays and array systems and methods therefor |
| US13/942,285 US20130299680A1 (en) | 2007-03-05 | 2013-07-15 | Sensor pixels, arrays and array systems and methods therefor |
| US14/096,572 US8872095B2 (en) | 2007-03-05 | 2013-12-04 | Sensor pixels, arrays and array systems and methods therefor |
| US14/499,144 US9281330B2 (en) | 2007-03-05 | 2014-09-27 | Sensor pixels, arrays and array systems and methods therefor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA002594737A CA2594737A1 (en) | 2007-07-13 | 2007-07-13 | High sensitivity a-si:h photo-transistor pixel with flicker noise reduction for near infra-red in-vivo bio-molecular imaging |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2594737A1 true CA2594737A1 (en) | 2009-01-13 |
Family
ID=40255113
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002594737A Abandoned CA2594737A1 (en) | 2007-03-05 | 2007-07-13 | High sensitivity a-si:h photo-transistor pixel with flicker noise reduction for near infra-red in-vivo bio-molecular imaging |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2594737A1 (en) |
-
2007
- 2007-07-13 CA CA002594737A patent/CA2594737A1/en not_active Abandoned
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| FZDE | Discontinued |