METHOD FOR CONTROLLING THRESHOLD VOLTAGE OF SEMICONDUCTOR ELEMENT

• US 20110076790A1
• Filed: 05/11/2009
• Published: 03/31/2011
• Est. Priority Date: 05/12/2008
• Status: Active Grant

• Current Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Original Assignee: Canon Kabushiki Kaisha (Canon Inc.)
• Inventors: Kawasaki, Takehiko, Ofuji, Masato, Hayashi, Ryo, Takai, Yasuyoshi, Kaneko, Norio
• Granted Patent: US 8,530,246 B2
• Time in Patent Office: Days
• US Class Current: 438/17
• CPC Class Codes: H01L 29/66969 of devices having semiconductor bodies not comprising group 14 or group 13/15 materials comprising selenium or tellurium in uncombined form other than as impurities in semiconductor bodies of other materials, comprising cuprous oxide or cuprous iodide H01L21/02365
• CPC Class Codes: H01L 29/7869 having a semiconductor body comprising an oxide semiconductor material, e.g. zinc oxide, copper aluminium oxide, cadmium stannate

Abstract

A method for controlling the threshold voltage of a semiconductor element having at least a semiconductor as a component is characterized in including a process to measure one of a threshold voltage and a characteristic value serving as an index for the threshold voltage; a process to determine one of the irradiation intensity, irradiation time, and wavelength of the light for irradiating the semiconductor based on one of the measured threshold voltage and the measured characteristic value serving as the index for the threshold voltage; and a process to irradiate light whose one of the irradiation intensity, irradiation time, and wavelength has been determined onto the semiconductor; wherein the light irradiating the semiconductor is a light having a longer wavelength than the wavelength of the absorption edge of the semiconductor, and the threshold voltage is changed by the irradiation of the light.

Claims

1. A method for controlling a threshold voltage of a semiconductor element comprised of a semiconductor, comprising:

measuring the threshold voltage or a characteristic value serving as an index for the threshold voltage;

determining an irradiation intensity, an irradiation time or a wavelength of light with which the semiconductor is irradiated by the measured threshold voltage or characteristic value; and

irradiating the semiconductor with the light;

the light having a longer wavelength than a wavelength of an absorption edge of the semiconductor, and the threshold voltage being changed by the irradiation of the light.

2. The method according to claim 1, wherein the characteristic value is a turn-on voltage of the semiconductor element.

3. The method according to claim 1, wherein the threshold voltage is changed in a direction opposite to the changing direction of a threshold voltage of the semiconductor element changed first.

4. The method according to claim 1, wherein the semiconductor is blocked from light having a shorter wavelength than the wavelength of the absorption edge of the semiconductor.

5. The method according to claim 1, wherein the semiconductor element has at least a gate electrode, a source electrode, a drain electrode, a channel layer, and a gate insulating layer;

the semiconductor being the channel layer.

19. The method according to claim 1, wherein a surface density of an in-gap level of the semiconductor is not higher than 10¹³ cm⁻

2 eV<sup>−

1</sup>.

20. The method according to claim 1, wherein the semiconductor is a semiconductor having a band gap of not less than 1.55 eV.

21. The method according to claim 1, wherein the semiconductor contains at least one element selected from In, Ga, Zn, and Sn.

6. A method for controlling a threshold voltage of a semiconductor element comprised of a semiconductor in a semiconductor device comprised of the semiconductor element and an electroluminescent element driven by the semiconductor element, comprising:

measuring the threshold voltage or a characteristic value serving as an index for the threshold voltage;

determining an irradiation intensity, an irradiation time or a wavelength of light with which the semiconductor is irradiated by the measured threshold voltage or characteristic value; and

irradiating the semiconductor with the light,

the light having a longer wavelength than a wavelength of an absorption edge of the semiconductor.

7. The method according to claim 6, wherein the characteristic value is a turn-on voltage of the semiconductor element.

8. The method according to claim 6, wherein the characteristic value serving as the index of the threshold voltage is one of a luminescence intensity and a penetrating electric current of the electroluminescent element.

9. The method according to claim 6, wherein the threshold voltage is changed in a direction opposite to the changing direction of a threshold voltage changed first.

10. The method according to claim 6, wherein the semiconductor is blocked from light having a shorter wavelength than the wavelength of the absorption edge of the semiconductor.

11. The method according to claim 6, wherein the semiconductor device includes a plurality of semiconductor elements;

the semiconductor device is equipped with one light source for collectively irradiating light onto the plurality of semiconductor elements when the plurality of semiconductor elements are close to one another; and

threshold voltage of the plurality of semiconductor elements is simultaneously changed by the one light source.

12. The method according to claim 11, wherein the semiconductor device includes a plurality of light sources for irradiating the light, and threshold voltages of a plurality of semiconductor elements are individually changed by the plurality of light sources.

13. The method according to claim 6, wherein the semiconductor element has at least a gate electrode, a source electrode, a drain electrode, a channel layer, and a gate insulating layer, the semiconductor being the channel layer.

14. The method according to claim 13, wherein the semiconductor device includes a light emitting diode as a light source, and at least a TFT driver circuit, a Vth measuring circuit, a light emitting diode controlling circuit and a memory as external circuits, and based on a time rate of change of the threshold voltage stored in the memory, one of irradiation intensity, irradiation time, and wavelength of the light irradiated onto the semiconductor is determined.

15. The method according to claim 13, wherein the semiconductor device includes a TFT array wherein the semiconductor elements are arranged in an array, a light emitting diode as a light source, and at least a gate driver, a source driver, a cathode driver, an anode driver, and a memory as external circuits, and based on a time rate of change of the threshold voltage stored in the memory, one of irradiation intensity, irradiation time, and wavelength of the light irradiated onto the semiconductor is determined.

16. The method according to claim 13, wherein the semiconductor device includes a reference element for measuring threshold voltage, and one of the threshold voltage of a reference element and a characteristic value that becomes the index for the threshold voltage in place of the semiconductor element is measured.

17. The method according to claim 13, wherein the semiconductor device includes a circuit that outputs a potential corresponding to a time integration value of a drain-source electric current of the semiconductor element in place of the circuit for measuring a Vth of the semiconductor element, and the potential obtained from the circuit that outputs the potential is used as the index for the threshold voltage.

18. The method according to claim 17, wherein in the semiconductor device the light emitting diode driver is constituted by a constant voltage power source for driving the light emitting diode and a switch connected in series to the constant voltage power source;

and the irradiation time of the light irradiated onto the semiconductor is determined without using a memory by providing a circuit that compares the reference potential Vref supplied from an exterior with a magnitude of the potential and holds the output, and connecting to the light emitting diode driver.