Microchannel plate devices with tunable conductive films
A microchannel plate includes a substrate defining a plurality of channels extending from a top surface of the substrate to a bottom surface of the substrate. A resistive layer is formed over an outer surface of the plurality of channels that provides ohmic conduction with a predetermined resistivity that is substantially constant. An emissive layer is formed over the resistive layer. A top electrode is positioned on the top surface of the substrate. A bottom electrode positioned on the bottom surface of the substrate.
1. A microchannel plate detector comprising: a substrate having a plurality of channels extending from a top surface of the substrate to a bottom surface of the substrate; a resistive layer having a resistance that is substantially constant as a function of applied voltage over an operating range of the microchannel plate detector, the resistive layer being formed by conformal deposition over the outer surface of the plurality of channels; and at least one electron emissive layer formed by conformal deposition over the resistive layer.
2. The microchannel plate of claim 1 , wherein the resistive layer consists of an alternating sequence of insulating and conducting layers.
3. The microchannel plate of claim 2 , wherein the conducting layers are comprised of candidate materials with no bandgap, interspersed within a large bandgap material.
4. The microchannel plate of claim 3 , wherein the resistive layer comprises a nanoalloy.
5. The microchannel plate of claim 2 , wherein the conducting layers comprise alternating layers of lower bandgap material higher bandgap material.
6. The microchannel plate of claim 5 , wherein the resistive layer comprises a nanolaminate.
7. The microchannel plate of claim 1 wherein a Temperature Coefficient of Resistance (TCR) of the resistive layer is less than one percent.
8. The microchannel plate of claim 1 , wherein the resistive layer and electron emissive layer provide a relative current gain for the microchannel plate that is greater than approximately 0.6 over an incident dose ranging between approximately 0.001 C-cm −2 and approximately 0.015 C-cm −2 .
9. The microchannel plate of claim 1 , wherein the resistive layer and electron emissive layer provide a relative current gain for the microchannel plate that is greater than approximately 0.8 over an incident dose ranging between approximately 0.001 C-cm −2 and approximately 0.015 C-cm −2 .
10. The microchannel plate of claim 5 , wherein the resistance of the resistive layer is substantially constant between the bias voltage values of approximately 500 volts and approximately 1,000 volts.
11. The microchannel plate of claim 1 , wherein a resistance of the resistive layer is determined by at least a dopant concentration within the resistive layer.
12. The microchannel plate of claim 1 , wherein a resistance of the resistive layer is determined by at least one layer thickness within the resistive layer.
13. The microchannel plate of claim 1 , wherein a resistance of the resistive layer is determined by at least a number of layers within the resistive layer.
14. The microchannel plate of claim 1 , wherein a resistance of the resistive layer is determined by a ratio of conductive to insulating layers within the resistive layer.
15. A method for making a microchannel plate detector, the method comprising: forming by conformal deposition a resistive layer over the outer surface of a plurality of channels that extend through a substrate; selectively tuning a resistivity of the resistive layer so that a resistance of the resistive layer is substantially constant as a function of applied voltage over an operating range of the microchannel plate detector; and forming, by conformal deposition, an electron emissive layer over the resistive layer.
16. The method of claim 15 , further comprising forming the resistive layer by an alternating sequence of insulating and conducting layers.
17. The method of claim 16 , further comprising forming the conducting layers by conformal deposition of candidate materials with no bandgap, interspersed within a large bandgap material.
18. The method of claim 17 , further comprising forming the resistive layer by conformal deposition of a nanoalloy.
19. The method of claim 15 , further comprising forming the conducting layers by conformal deposition of candidate materials with moderate bandgap in alternating layers with a large bandgap material.
20. The method of claim 19 , further comprising forming the resistive layer by conformal deposition of a nanolaminate.
21. The method of claim 15 , further comprising forming the resistive layer for which the Temperature Coefficient of Resistance (TCR) is less than one percent.
22. The method of claim 15 , further comprising forming the resistive layer and electron emissive layer to provide a relative current gain for the microchannel plate that is greater than 0.6 over an incident dose ranging between approximately 0.001 C-cm −2 and 0.015 C-cm −2 .
23. The method of claim 15 , wherein forming the resistive layer and electron emissive layer to provide the relative current gain comprises controlling at least one of a thickness of a layer within the resistive layer, a dopant concentration of at least one layer within the resistive layer, a ratio of conductive to insulating layers within the resistive layer, or a thickness of the resistive layer.
24. The method of claim 15 , further comprising forming the resistive layer and electron emissive layer to provide a relative current gain for the microchannel plate that is greater than 0.8 over an incident dose ranging between approximately 0.001 C-cm −2 and 0.015 C-cm −2 .
25. The method of claim 15 , further comprising forming the resistive layer to provide a resistance that is constant between the bias voltages values of approximately 500 volts and 1,000 volts.
26. The method of claim 15 , wherein selectively tuning the resistivity comprises controlling a dopant concentration within the resistive layer to set the resistivity of the resistive layer to a selected value.
27. The method of claim 15 , wherein selectively tuning the resistivity comprises controlling at least one layer thickness within the resistive layer to set the resistivity of the resistive layer to a selected value.
28. The method of claim 15 , further comprising controlling a number of layers within the resistive layer to set a resistance of the resistive layer to a selected value.
29. The method of claim 15 , wherein selectively tuning the resistivity comprises controlling a ratio of conductive to insulating layers within the layer to set the resistivity of the resistive layer to a selected value.
30. A microchannel plate comprising:
a) a substrate defining a plurality of channels extending from a top surface of the substrate to a bottom surface of the substrate;
b) a resistive layer comprising a nanolaminate structure formed over an outer surface of the plurality of channels, the nanolaminate structure being chosen to have a composition that provides ohmic conduction with a predetermined resistivity that is substantially constant over an operating range of the microchannel plate detector;
c) an emissive layer formed over the resistive layer; and
d) a top electrode positioned on the top surface of the substrate; and a bottom electrode positioned on the bottom surface of the substrate.