Method and apparatus for fabricating mercuric iodide polycrystalline films for digital radiography

• US 20030021382A1
• Filed: 05/30/2002
• Published: 01/30/2003
• Est. Priority Date: 07/30/2001
• Status: Active Grant

• Current Assignee: Rapiscan Laboratories Incorporated (OSI Systems Incorporated)
• Original Assignee: DxRay, Inc. (OSI Systems Incorporated)
• Inventors: Patt, Bradley E., Iwanczyk, Jan S.
• Granted Patent: US 7,186,985 B2
• Time in Patent Office: Days
• US Class Current: 378/175
• CPC Class Codes: C23C 14/0694 Halides
• CPC Class Codes: C23C 14/24 Vacuum evaporation
• CPC Class Codes: C23C 14/564 Means for minimising impurities in the coating chamber such as dust, moisture, residual gases
• CPC Class Codes: H01L 27/14676 X-ray, gamma-ray or corpuscular radiation imagers measuring X-, gamma- or corpuscular radiation G01T1/00
• CPC Class Codes: H01L 31/115 Devices sensitive to very short wavelength, e.g. X-rays, gamma-rays or corpuscular radiation
• CPC Class Codes: H04N 23/30 for generating image signals from X-rays
• CPC Class Codes: H04N 5/32 Transforming X-rays cameras or camera modules for generating image signals from X-rays H04N23/30; circuitry of SSIS for transforming X-rays into image signals H04N25/30

Abstract

A method is provided for fabricating in a thermal evaporation system a polycrystalline film capable of directly detecting radiation. Source material is placed in a container, and the container is evacuated to create vacuum within the container. The source material is heated to evaporate the source material for depositing on a substrate. The polycrystalline film is used in as deposited form to detect the radiation.

Claims

1. A method of fabricating a polycrystalline film in a thermal evaporation system, the polycrystalline film being capable of directly detecting radiation, the method comprising:

placing source material in a container;

evacuating the container to create vacuum within the container; and

heating the source material to evaporate the source material, wherein the evaporated source material is deposited on a substrate,

wherein the polycrystalline film is used in as deposited form to detect the radiation.

2. The method according to claim 1, further comprising purifying the source material prior to placing it in the container.

3. The method according to claim 2, wherein purifying comprises purifying through 4XMS purification.

4. The method according to claim 2, wherein purifying comprises:

subliming the source material in vacuum, thereby removing impurities from the source material;

melting the source material, whereby remaining impurities are separated from the source material;

cooling the molten source material;

subliming the cooled source material; and

passing the sublimed source material through a ceramic frit but not the impurities.

5. The method according to claim 1, wherein the source material comprises mercuric iodide (HgI₂).

6. The method according to claim 1, further comprising synthesizing the source material from starting compounds, wherein the starting compounds are purified prior to the synthesis of the source material.

7. The method according to claim 6, wherein the starting compounds comprise mercuric chloride (HgCl₂) and potassium iodide (KI).

8. The method according to claim 1, further comprising controlling temperature of the substrate within a predetermined range.

9. The method according to claim 8, wherein the predetermined temperature range for the substrate is between 20°

C. and 85°

C.

10. The method according to claim 8, wherein controlling temperature of the substrate comprises maintaining a substantially uniform temperature throughout the substrate.

11. The method according to claim 1, wherein heating comprises maintaining temperature of the source material within a predetermined range.

12. The method according to claim 11, wherein the predetermined temperature range for the source material is between 120°

C. and 160°

C.

13. The method according to claim 1, wherein evacuating comprises evacuating the container to between 10⁻

5 Torr and 10<sup>−

7</sup> Torr.

14. The method according to claim 1, wherein the substrate is fabricated from material selected from a group consisting of silicon, glass and alumina.

15. The method according to claim 1, wherein the substrate has electronic readout circuitry formed thereon.

16. The method according to claim 15, wherein the electronic readout circuitry is based on a technology selected from a group consisting of TFT and CMOS technologies.

17. The method according to claim 1, wherein the polycrystalline film is capable of directly detecting X-rays by converting the X-rays to an electrical signal.

18. A thermal evaporation system for fabricating a polycrystalline film, the polycrystalline film being capable of directly detecting radiation, the system comprising:

a container adapted for creating vacuum within and for heating source material disposed therein;

a furnace enclosing at least a portion of the container, the furnace being capable of heating the container to evaporate the source material;

a substrate holder for holding the substrate, on which the evaporated source material is deposited for growth of the polycrystalline film; and

a temperature controlling system for maintaining the source material and the substrate at respective predetermined temperature ranges to control a growth rate of the polycrystalline film, whereby the polycrystalline film is capable of being applied in a radiation detector.

19. The thermal evaporation system according to claim 18, wherein the temperature controlling system comprises:

at least one thermocouple for measuring temperature in the furnace;

a heating element capable of controlling the temperature about the container; and

a cooler capable of controlling the temperature of the substrate.

20. The thermal evaporation system according to claim 19, further comprising a temperature controller for controlling the heating element and the cooler in response to the measured temperature.

21. The thermal evaporation system according to claim 18, further comprising a vacuum system for maintaining vacuum within the container.

22. A radiography system comprising:

an array detector capable of receiving radiation and generating corresponding electrical signal, the array detector comprising a polycrystalline film fabricated through sublimation on a readout substrate, wherein the polycrystalline film is used in as deposited form after being grown on said readout substrate; and

an image processor coupled to the array detector to generate a displayable image from the electrical signal.

23. The radiography system according to claim 22, further comprising:

a plurality of first electrodes formed on the readout substrate; and

a second electrode formed on the polycrystalline film,

wherein a bias voltage applied between the first and second electrodes creates an electric field within the polycrystalline film, said electric field facilitating signal formation in response to an x-ray radiation.

24. The radiography system according to claim 22, further comprising a plurality of first electrodes formed on the substrate and a plurality of second electrodes formed on the polycrystalline film, wherein the first and second electrodes are dispose perpendicularly to one another.

25. The radiography system according to claim 22, further comprising:

a-plurality of first electrodes formed on the readout substrate; and

a thin layer of insulator material coated on the readout substrate by depositing said insulator material on a surface of the readout substrate on which the first electrodes are formed,

wherein the thin layer of insulator material forms a blocking barrier between the first electrodes and the polycrystalline film in order to control a flow of current and to chemically isolate the polycrystalline film from the first electrodes.

26. The radiography system according to claim 23, further comprising a plurality of pre-amplifiers, each pre-amplifier capable of processing signal from one of the first electrodes.

27. The radiography system according to claim 22, further comprising a plurality of pre-amplifiers, each pre-amplifier capable of processing signal from one of the first and second electrodes.

28. The radiography system according to claim 22, wherein the image processor comprises an analog-to-digital converter for digitizing the electrical signal.

29. The radiography system according to claim 22, further comprising a display capable of displaying the displayable image.

30. The radiography system according to claim 22, wherein the radiation comprises X-ray.