Sensor cell

• US 20020117694A1
• Filed: 12/20/2001
• Published: 08/29/2002
• Est. Priority Date: 12/22/2000
• Status: Active Grant

• Current Assignee: Cambridge University (Government of United Kingdom), Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Lowe, Christopher, Migliorato, Piero, Bavidge, Nathan
• Granted Patent: US 6,657,269 B2
• Time in Patent Office: Days
• US Class Current: 257/253
• CPC Class Codes: G01N 27/27 Association of two or more measuring systems or cells, each measuring a different parameter, where the measurement results may be either used independently, the systems or cells being physically associated, or combined to produce a value for a further parameter
• CPC Class Codes: G01N 27/4145 specially adapted for biomolecules, e.g. gate electrode with immobilised receptors
• CPC Class Codes: G01N 27/4148 Integrated circuits therefor, e.g. fabricated by CMOS processing CMOS processing per se H01L21/82

Abstract

A sensor cell comprises receiving means, which may be in the form of an electrode 10 coupled to the gate electrode of a thin film transistor T1. In one form of the invention a voltage supplied to the gate electrode of the transistor T1 via a switching transistor T7 is controlled in dependence upon the value of capacitance C_A arising at the electrode from receipt of a sample for identification. Thus, the operation of transistor T1 can be used to identify the sample received by the electrode 10.

Claims

1. A sensor cell comprising a thin film transistor and receiving means coupled to a gate electrode of the thin film transistor for receiving a sample for identification.

2. A sensor cell as claimed in claim 1, wherein the receiving means comprises a sample electrode, the arrangement being such that operation of the thin film transistor is controlled in dependence upon a value of capacitance arising at the sample electrode in response to receipt by the sample electrode of the sample for identification.

3. A sensor cell as claimed in claim 2, comprising a reference capacitor and wherein the sample electrode and the reference capacitor are arranged as a capacitance divider circuit coupled to the gate electrode of the thin film transistor for controlling the amplitude of a voltage pulse provided to the gate electrode in dependence upon the value of capacitance arising at the sample electrode.

4. A sensor cell as claimed in claim 3, wherein the reference capacitor comprises the gate electrode and a buried region underlying a metal layer extending into contact with the gate electrode and separated from the metal layer by an insulator layer.

5. A sensor cell as claimed in claim 4, wherein the buried region comprises metal or doped polysilicon.

6. A sensor cell as claimed in any one of claims 3 to 5 comprising a further transistor for affording the voltage pulse to the gate electrode of the thin film transistor in response to a select pulse afforded to the further transistor.

7. A sensor cell as claimed in claim 6, wherein the further transistor comprises a thin film transistor.

8. A sensor cell as claimed in claim 2 comprising a switching transistor for switching between a conducting condition and a nonconducting condition, the arrangement being such that a voltage provided to the gate electrode of the thin film transistor with the switching transistor in the conducting condition changes in magnitude in dependence upon the value of the capacitance arising at the sample electrode when the switching transistor is switched to the non-conducting condition.

9. A sensor cell as claimed in claim 8 comprising a select line for providing a select pulse to a gate electrode of the switching transistor for switching the switching transistor between the conducting and non-conducting conditions.

10. A sensor cell as claimed in claim 9 comprising a preset line for providing the voltage to the gate electrode of the thin film transistor and a read line for providing a read voltage to the thin film transistor, the arrangement being such that a preset cycle is enabled by providing the select pulse to the switching transistor, thereby to switch the switching transistor to a conducting condition to enable the voltage to be provided to the gate electrode of the thin film transistor, and wherein a read cycle is enabled by terminating the select pulse thereby to switch the switching transistor to the non-conducting condition, whereby the voltage at he gate electrode of the thin film transistor changes in magnitude, thereby to switch the thin film transistor to a non-conducting condition, the time taken between termination of the select pulse and switching of the thin film transistor to the non-conducting condition being dependent upon the value of capacitance at the sample electrode.

11. A sensor cell as claimed in any one of claims 3 to 7, comprising a threshold voltage compensation circuit including a constant current source for providing a preset level of current through the thin film transistor and switching means for selectively coupling the constant current source to the thin film transistor.

12. A sensor cell as claimed in claim 11 comprising an additional transistor coupled to the thin fix transistor, the arrangement being such that when the voltage pulse is provided to the gate electrode of the thin film transistor and the constant current source is decoupled from the thin film transistor, the magnitude of an output current from the thin film transistor will change from a first level determined by the constant current source to a second level dependent upon the value of capacitance arising at the sample electrode.

13. A sensor cell as claimed in claim 12 comprising means for determining the change between the first and second levels of the output current from the thin film transistor.

14. A sensor cell as claimed in any one of claims 11 to 13, wherein the switching means comprises a thin film transistor switching circuit.

15. A sensor cell as claimed in any one of the preceding claims, wherein the receiving means comprises gold, silver or platinum.

16. A sensor cell as claimed in anyone of the preceding claims, wherein the receiving means is arranged in a position offset from the thin film transistor, the arrangement being such that the sample is received by the receiving means in a position which does not overlie a gate region of the thin film transistor.

17. A sensor cell as claimed in claim 1 or 2, wherein the receiving means comprises a well portion arranged in a passivation layer overlying the film transistor thereby to provide a layer of passivation material overlying a metal layer extending into contact with te gate electrode, the layer of passivation material having a thickness such that an electric charge arising in the well portion from receipt by the well portion of the sample for identification creates a voltage at the gate electrode of the thin film transistor indicative of the sample.

18. A sensor cell as claimed in any one of the preceding claims, wherein the sensor cell comprises a plastics or glass substrate.

19. A sensor comprising an array of rows and columns of sensor cells as claimed in any one of the preceding claims.

20. A sensor as claimed in claim 19 comprising a row select register for selecting the rows of sensor cells of the array and a column select register for selecting the columns of sensor cells of the array.

21. A sensor as claimed in claim 19 or 20 comprising amplification means for amplifying output signals from the sensor cells.

22. A sensor as claimed in any one of claims 19 to 21 comprising multiplexing means for multiplexing output signals from the sensor cells.

23. A sensor as claimed in any one of claims 19 to 22 comprising storage means for storing reference values indicative of reference samples, comparator means for comparing the reference values with output signals from sensor cells and display means arranged to indicate whether a sample for identification matches a reference sample.

24. A sensor as claimed in any one of claims 19 to 23, wherein each sensor cell comprises a reference electrode, and wherein a plurality of reference electrodes disposed in spaced relationship throughout the array are arranged to carry a common reference substance, and the sensor farther comprises circuit means for receiving and averaging output signals from those sensor cells including one of the plurality of reference electrodes carrying the common reference substance.

26. A method as claimed in claim 25, comprising providing Be receiving means in a position offset from the thin film transistor such that the sample is received by the receiving means in a position which does not overlie a gate region of the thin film transistor.

27. A method as claimed in claim 25 or 26, comprising providing the receiving means as a sample electrode and wherein the operation of the thin film transistor is controlled in dependence upon a value of capacitance arising at the sample electrode in response to receipt by the sample electrode of the sample.

28. A method as claimed in claim 27 comprising providing a reference capacitor and arranging the reference capacitor and the sample electrode as a capacitance divider circuit coupled to the gate electrode of the thin film transistor, and controlling the amplitude of a voltage pulse provided to the gate electrode in dependence upon the value of capacitance arising at the sample electrode.

29. A method as claimed in claim 28 comprising providing the reference capacitor as a buried region underlying a metal layer extending into contact with the gate electrode and separated from the metal layer by an insulator layer.

30. A method as claimed in claim 29 comprising providing the buried region as a region of metal or doped polysilicon.

31. A method as claimed in claim 28 comprising providing a further transistor and controlling the voltage pulse provided to the gate electrode by applying a select pulse to the further transistor.

32. A method as claimed in claim 31 comprising supplying the further transistor as a thin film transistor.

33. A method as claimed in claim 27 comprising coupling the sample electrode with a switching transistor for switching between a conducting condition and a nonconducting condition, providing a voltage to the gate electrode of the Win film transistor with the switching transistor in the conducting condition, and coupling the sample electrode to the switching transistor, whereby when the switching transistor is switched to the non-conducting condition the voltage provided to the gate electrode of the tin film transistor changes in magnitude in dependence upon the value of the capacitance arising at the sample

34. A method as claimed in claim 33, wherein the switching transistor is, switched between the non-conducting and conducting conditions by providing a select pulse a select line to the switching transistor.

35. A method as claimed in claim 34 comprising providing a preset line for providing the voltage to the gate electrode of the thin film transistor, a read line for providing a read voltage to the thin film transistor, enabling a preset cycle by providing the select pulse to the switching transistor, thereby to switch the switching transistor to a conducting condition to provide the voltage to the gate electrode of the thin film transistor, and enabling a read cycle by terminating the select pulse thereby to switch the switching transistor to the non-conducting condition, whereby the voltage at the gate electrode of the thin film transistor changes in magnitude, thereby to switch the thin film transistor to a non-conducting condition, He time taken between the termination of the select pulse and switching of the thin film transistor to the non-conducting condition being dependent upon the value of capacitance at the sample electrode.

36. A method as claimed in any one of claims 28 to 30 comprising providing a threshold voltage compensation circuit including a constant current source for providing a preset level of current through the thin film transistor, and switching means for selectively coupling the constant current source to the thin film transistor.

37. A method as claimed in claim 36 comprising coupling an additional transistor to the thin film transistor, providing the voltage pulse to the gate electrode of the thin film transistor and decoupling the constant current source from the Win film transistor thereby to change the magnitude of the output current from the thin film transistor from a first level determined by the constant current source to a second level dependent upon the value of capacitance arising at the sample electrode.

40. A method as claimed in any one of claim 25 to 38 comprising providing a plurality of sensor cells arranged as an array of rows and columns of sensor cells.

41. A method as claimed in claim 40 comprising providing a row select register for selecting the rows of sensor cells in the array and a column select register for select the columns of sensor cells of the array.

42. A method as claimed in claim 40 or 41 comprising providing amplification means for amplifying output signals from the sensor cells.

43. A method as claimed in any one of claims 40 to 42 comprising providing multiplexing means for multiplexing output signals from the sensor cells.

44. A chemical sensor comprising a sensor cell as claimed in any one of claims 1 to 18 or a sensor as claimed in any one of claims 19 to 24.

45. Fingerprint recognition apparatus comprising a sensor cell as claimed in any one of claims 1 to 18 or a sensor as claimed in any one of claims 19 to 24.

25. A method for identifying a sample comprising providing a sensor cell including a thin film transistor and receiving means coupled to a gate electrode of the thin film transistor for receiving the sample.

38. A method as claimed in claims 25 or 26, wherein the receiving means is provided as a well portion arranged in a passivation layer overlying the thin film transistor so as to provide a layer of passivation material overlying a metal layer extending into contact with the gate electrode, the layer passivation material having a thickness such that an electric charge arising in the well portion from receipt by the well portion of the sample for identification creates a voltage at the gate electrode of the thin film transistor indicative of the sample.

39. A method as claimed in any one of claims 25 to 37, comprising fabricating the sensor cell on a plastics or a glass substrate.

46. A method of operating a biosensor comprising a method as claimed in any one of claims 25 to 43.

47. A method of operating fingerprint recognition apparatus comprising a method as claimed in any one of claims 25 to 43.