Patent Description:
Unfortunately, image intensifiers that rely on electron impact ionization as a gain mechanism often experience performance degradation when electrons move along undesirable paths prior to or subsequent to an impact. For example, if electrons backscatter (reflect or bounce) off a surface of the electron multiplier, these backscattered electrons may create a halo effect that degrades image quality. Additionally or alternatively, some electrons, including backscattered electrons, may be lost between the photocathode layer and the electron multiplier (i.e., if the electrons are absorbed by a structure other than the electron multiplier). Still further, electrons may move laterally within the electron multiplier, thereby degrading the spatial fidelity of the electrons that are output by the electron multiplier. Thus, crosstalk between pixels or adjacent regions in the gain layer may cause performance degradation. To minimize performance degradation, the thickness of the gain layer is often minimized. However, a thin gain layer is susceptible to failure from mechanical breakage or other processes such as deflection from pressure differentials between cavities or from applied voltages between different layers.

<FIG> shows an example of an image intensifier, in this case, a CERN Tynode, which includes thin transmission layers to minimize performance degradation (see, https://indico. ch/event/<NUM>/contributions/<NUM>/attachments/<NUM>/<NUM>/WIT2 <NUM>. In this example, the top layer (shown) and bottom layer (not shown) is thick, while the inner layers (shown) are thin. The thin layers may deform under shock and vibration or may exhibit failure due to repeated flexing from applied voltages. Additionally, these thin membranes are susceptible to breakage and/or electrical failure.

<FIG> shows another example of an image intensifier. This device, which comprises a thick silicon layer with channels, is considerably complex and difficult to manufacture. In this structure, bonded regions surrounding active areas provide robustness. However, this design has the disadvantage of signal loss in the bonded regions (see, https://www. gov/servlets/purl/<NUM>). Electrons emitted from the photocathode have radial energy (not just tangential energy) so if the channels are too long, the electrons will impact the sides before reaching the next receiving surface.

Increasing the thickness of the gain layer to add support or adding other specialized features to the gain layer generally leads to signal degradation and may increase manufacturing complexity. Thus, there is a tradeoff between the thickness of the gain layer and the ability of the carriers to pass through the gain layer without signal loss or degradation of the carriers.

According to an embodiment, an electron multiplier for a Micro-Electro-Mechanical-Systems (MEMS) image intensifier includes a photocathode, a transmission or gain substrate layer, and a phosphor or sensing layer (also referred to as an anode). The photocathode layer comprises an input surface that receives electrons and an emission surface (opposite the input surface) that emits electrons into a vacuum or gap. The emitted electrons pass through the vacuum to an input surface of the gain substrate layer. The received electrons are amplified by the gain substrate layer, and are emitted into a vacuum at an emission surface (opposite the input surface) of the gain substrate layer. A first plurality of support ribs are present on the input surface of the gain substrate layer, and a second plurality of support ribs are present on the emission surface of the gain substrate layer, adding mechanical support to the thin gain substrate layer while minimizing signal degradation and loss.

In some aspects, the height of the first plurality of ribs and the height of the second plurality of ribs are about the same. In other aspects, the height of the first plurality of ribs is less than the height of the second plurality of ribs. In still other aspects, the height of the first plurality of ribs is greater than the height of the second plurality of ribs.

According to another embodiment, the height of the first plurality of ribs and the height of the second plurality of ribs are each set to provide a predetermined degree of mechanical rigidity to the gain substrate layer.

In other aspects, the spacing between the individual ribs of the first plurality of ribs are configured to allow electrons emitted from the photocathode to be received on the input surface of the gain substrate layer without substantial degradation from contacting the walls of the first plurality of ribs. The spacing is determined at least in part by the distance between the emission surface of the photocathode and the input surface of the gain substrate layer (gap distance). Similarly, the spacing between the individual ribs of the second plurality of ribs are configured to allow electrons to be emitted from the emission surface of the gain substrate layer without substantial degradation from contacting the walls of the second plurality of ribs. The radial spread of electrons may be determined by the following equation: <MAT> wherein the gap is the distance between surfaces (e.g., between the emission surface of the photocathode and the input surface of the gain substrate layer), MTE is the mean transverse energy of the emitted electrons, and Vbias is the bias between the two surfaces.

In general, the individual ribs of the first plurality of ribs are aligned with respective individual ribs from the second plurality of ribs. For example, each individual rib of the first plurality of ribs may be positioned such that a vertical axis passes through a rib of the first surface, through the gain substrate layer and through a corresponding rib of the second plurality of ribs.

In another aspect, blocking structures/regions can be used in a transmission mode image intensifier to maintain the spatial registration of carriers in the gain substrate layer. Ribs, on both the upper input surface and lower emission surface, may be used to increase the robustness of the thin silicon-based gain substrate layer.

Like reference numerals have been used to identify like elements throughout this disclosure.

A gain substrate layer for a MEMS image intensifier is presented herein. The gain substrate layer includes a first plurality of ribs on an upper input surface and a second plurality of ribs on a lower emission surface. In some aspects, each of the upper ribs is aligned with a corresponding lower rib.

The gain substrate layer presented herein includes p-type doped ribs on both the upper input surface and the lower emission surface. The ribs define a plurality of cells, or pixels, insofar as the term "doped" or variants thereof (e.g., referred to herein as doping, dopant, etc.) indicates that a dopant has been added to shift the Fermi levels within the silicon-based material, such that with p-type dopants, the ribs are shifted to predominantly positive charge carriers. Advantageously, since the ribs comprise a p-type doped material, the ribs prevent electron crosstalk between pixels. According to an embodiment, the ribs extend above an input surface of the gain substrate layer (e.g., electron multiplier) and below the output emission surface of the gain substrate layer. Further, halo effects created by backscattered electrons are minimized by the ribs, only on the input surface 312a.

By extending lateral spacers perpendicular to or substantially perpendicular to the input surface and emission surface of the gain substrate layer, height may be added to the thin gain substrate layer, as a grid type, post type, or other suitable structure, to provide mechanical support while maintaining signal integrity. Thus, an enhanced thin gain substrate layer (also referred to as an electron multiplier layer or a transmission layer), which is ideal for maintaining spatial registration of carriers (e.g., holes) in the electron multiplier layer, can be generated by modifying a thin gain substrate layer to include a first plurality of upper ribs and a second plurality of lower ribs in order to be mechanically robust over large areas while maintaining signal integrity.

Typically, ribs that extend above the input surface of the gain substrate layer cause at least some electrons to be lost between the cathode layer and the gain substrate layer (e.g., electrons that impact a surface of a rib may be lost). This effect may be minimized by reducing a first gap distance between the gain substrate layer and the photocathode layer, as well as by controlling the spacing of the ribs, or by varying the voltage according to Eq. (<NUM>).

The image intensifier provided herein is intended to be an example. The electron multiplier can be included in any MEMS image intensifier or light detection device now known or developed hereafter.

<FIG> shows a high level cross-sectional view of a MEMS image intensifier <NUM> according to an embodiment. The MEMS image intensifier comprises a photocathode <NUM>, a gain substrate layer <NUM>, and anode <NUM>. A vacuum (first gap) separates the photocathode from the gain substrate layer. A vacuum (second gap) also separates the gain substrate layer from an anode. The vacuum layer allows the signal to be maintained, rather than undergo degradation from passing through another layer of a material.

The layers are encapsulated in an appropriate vacuum housing <NUM>, and may be connected to an external power supply comprising bias circuitry <NUM> to bias the physical layers of the device to suitable voltages. More specifically, the bias circuitry <NUM> may include one or more circuits to appropriately bias photocathode <NUM>, gain substrate layer <NUM>, and anode <NUM> of the MEMS image intensifier <NUM>. The MEMS image intensifier is described in further detail below.

<FIG> shows a cross-sectional view of MEMS image intensifier <NUM>, with a gain substrate layer configured to multiply electrons in accordance with example embodiments as provided herein. MEMS image intensifier <NUM> includes photocathode <NUM>, a gain substrate layer <NUM>, and a phosphor/sensing layer <NUM> (also referred to as an anode layer). The phosphor/sensing layer may be coupled to a screen/display <NUM>, allowing a user to visualize the output of the gain substrate layer. In some aspects, a first vacuum or first gap distance <NUM> is present between the photocathode <NUM> and the gain substrate layer <NUM>. A second vacuum or second gap distance <NUM> is present between the phosphor/sensing layer <NUM> and the gain substrate layer <NUM>. Region 455a corresponds to the height of ribs 420a, while region 455b corresponds to the height of ribs 420b.

Various fabrication processes may be used to form the ribs. To form the first plurality of ribs 420a, a silicon-based layer may be generated on the input surface of the gain substrate layer with a height corresponding to the height of region 455a. Known fabrication processes involving etching may be used to form ribs, as posts, walls, etc. After etching, ribs are present in the active region <NUM>, with region 455a intact.

To form the second plurality of ribs 420b, polysilicon-based layers may be built up on the emission layer of the gain substrate layer, to reach a height corresponding to the height of region 455b. Ribs are generated in the active region <NUM>, with region 455b intact. Additional details regarding fabrication of the gain substrate layer are provided herein.

Region <NUM> represents a first gap distance between the tip of ribs 420a and photocathode <NUM>. Region <NUM> represents a second gap distance between the tip of ribs 420b and phosphor/sensing layer <NUM>.

The photocathode <NUM> includes an upper surface 405a and an output emission surface 405b. Pliotons <NUM>, present in regions outside of the image intensifier, may contact the photocathode <NUM> to convert photons to electrons. When photons <NUM> impinge on the upper surface 405a of the photocathode <NUM>, each impinging photon <NUM> has an associated probability of generating a free electron. Free electrons (e-) resulting from impinging photons <NUM> pass through photocathode <NUM> and are emitted from output emission surface 405b. In some aspects, the output emission surface 405b is activated to or configured to a negative electron affinity (NEA) state, using well-known techniques, to facilitate the flow of the free electrons (e-) from the output emission surface 405b of the photocathode into the first gap distance <NUM> of the vacuum.

In some aspects, photocathode <NUM> is a photocathode layer comprising semiconductor materials such as gallium arsenide (GaAs), which exhibits a photoemissive effect. It is noted that other type III-V materials may be used, including but not limited to GaP, GaInAsP, InAsP, InGaAs, etc. Alternatively, the photocathode may comprise a known bi-alkali material, which includes but is not limited to antimony-rubidium-cesium (Sb-Rb-Cs), antimony-potassium-cesium (Sb-K-Cs), sodium-potassium-antimony (Na-K-Sb), etc., which also has a photoemissive effect.

In this example, the photoemissive semiconductor material of the photocathode <NUM> absorbs photons at the upper surface 405a. The absorbed photons cause the carrier density of the semiconductor material to increase, thereby causing the photo-emissive semiconductor material to generate a photo-current of electrons (as shown by the arrows) passing through photocathode <NUM> for emission from the output emission surface 405b. In some aspects, photocathode <NUM> comprises blocking structures <NUM> (shown as triangles). The blocking structures are configured to focus the electrons (e.g., into streams of emitted electrons) as the electrons leave the photocathode <NUM> to travel through the first gap distance <NUM> to reach the gain substrate layer. Thus, the photocathode <NUM> convert photons <NUM> received from ambient light to electrons (e-), and releases these electrons towards the gain substrate layer <NUM> in streams that are spatially co-located with the open area between ribs 420a in the input surface 412a of the gain substrate layer <NUM>.

The gain substrate layer <NUM>, which may also be referred to as an electron multiplier layer or transmission layer, includes an input surface 412a and an emission surface 412b that is opposite the input surface 412a. Photocathode <NUM> is positioned above the input surface 412a, separated by first gap distance <NUM>, such that the photocathode <NUM> emits electrons towards the input surface 412a.

Gain substrate layer <NUM> may include silicon and/or other semi-conductive materials such as, and without limitation, gallium arsenide (GaAs). In an embodiment, gain substrate layer includes silicon-based component(s) and is doped with a p-type dopant to generate a plurality of electrons <NUM> for each free electron <NUM> that impinges on an input surface 412a of the gain substrate layer.

An electric field (not shown) between the photocathode <NUM> and the gain substrate layer <NUM> accelerates the electrons emitted by the photocathode towards the gain substrate layer, causing the electrons to impact the input surface 412a of the gain substrate layer <NUM>. The gain substrate layer <NUM> amplifies the received electrons forming electrons <NUM> and emits additional electrons (designated as Ge- and referred to as an electron interaction volume), via emission surface 412b, towards the phosphor/sensing layer <NUM>. Thus, there is a gain of electrons through the gain substrate layer <NUM>.

The gain substrate layer <NUM> provides a highly efficient gain, which allows the MEMS image intensifier <NUM> (more specifically, the phosphor/sensing layer <NUM> and screen/display <NUM>) to output visible light that a user can view in a direct view system (e.g., a system where a user looks directly at screen/display <NUM> for an image) or in a digital system (e.g., a system where a user views a digital output from a camera focused on a phosphor screen).

The gain substrate layer <NUM>, which may be formed using a wafer or other suitable substrate (e.g., a silicon-based substrate), comprises an active region <NUM> that is configured to receive and amplify electrons emitted by the photocathode <NUM>. The active region <NUM> includes a lattice or grid of interior walls or posts, referred to as a first plurality of ribs 420a, positioned on the input surface 412a and formed, for example, using single crystal silicon processes such as etching (a subtractive process), or another suitable process.

Another lattice or grid of interior walls or posts, referred to as a second plurality of ribs 420b, positioned on the emission surface 412b and formed, for example, using polysilicon crystal or boron doped polysilicon processes (additive processes), or another suitable process. In some aspects, to create the second plurality of ribs 420b, doping profiles may be generated by trenching, and polysilicon deposition may be used to form layer(s). In some aspects, processes such as Lithography, Electroplating, and Molding (LIGA) or other processes may be used to build up polysilicon layers. In some aspects, a thick photoresist applied to emission surface 412b may be used to build up polysilicon layers to form the plurality of second ribs, also using an additive process.

Ribs 420a or 420b may be formed on the input surface 412a or emission surface 412b, respectfully, using any suitable fabrication technique that generates a lattice or grid of walls or posts. Blocking structures <NUM> may be formed along the emission surface 412b, in order to focus the flow of emitted electrons to the anode <NUM>. Since the blocking structures are formed from a doped material (e.g., a p-doped material), the blocking structures prevent, or at least discourage, electrons from moving laterally within the gain substrate layer <NUM>, because the doped material produces an electrostatic barrier (i.e. an electric field that repels negative charged carriers). The barriers or blocking structures <NUM> are described in further detail below (<FIG> and <FIG>).

The MEMS image intensifier <NUM> may be configured to optimize individual electron paths through the various layers of the device. For example, individual components of the blocking structures <NUM>, ribs 420a, blocking structures <NUM>, and ribs 420b may be aligned such that an electron is directed along a vertical axis through these various layers and gaps, to prevent signal degradation from electrons moving horizontally. Thus, an electron stream may originate in the photocathode layer, pass through the vacuum and in between ribs 420a to enter the gain substrate layer, and pass through the gain substrate layer between blocking structures <NUM>, to exit between ribs 420b to reach the anode layer. Accordingly, the path may follow or track along a vertical axis to focus the emission of electrons in streams towards the phosphor/sensing layer <NUM>. In other aspects, the first and second plurality of ribs 420a, 420b, and blocking structures <NUM> may be aligned in order to maximize signal gain. By aligning the ribs, and blocking structure <NUM>, the flow of electrons is directed and signal gain is optimized through the gain substrate layer. In other aspects, the gain substrate layer may provide suitable electron multiplication without blocking structures <NUM>; however, the first plurality of ribs 420a and the lower ribs 420b are aligned.

Thus, in some aspects, the first and second plurality of ribs 420a, 420b, are aligned to form a plurality of pixels, such that the regions between ribs correspond to a pixel. Areas or pixels on the upper input surface and lower emission surface are aligned as a result. Electrons entering the gain substrate layer are amplified during passage along a vertical axis, wherein the electrons enter a region corresponding to a first input pixel on the upper input surface and exit a region of a corresponding first output pixel on the lower emission surface (as shown by arrows in <FIG> and <FIG>).

In some aspects, ribs 420a are made of p-type doped material and are in contact with or extend, at least slightly, into the input surface 412a of the gain substrate layer <NUM>. Similarly, ribs 420b are made of p-type doped material and are in contact with or extend, at least slightly, into the emission surface 412b of the gain substrate layer <NUM>. The first plurality of ribs 420a is perpendicular or substantially perpendicular to the input surface 412a, and the second plurality of ribs 420b is perpendicular or substantially perpendicular to the emission surface 412b, respectfully.

The phosphor/sensing layer <NUM> is positioned below the emission surface 412b of the gain substrate layer <NUM>, such that the phosphor/sensing layer <NUM> may receive electrons emitted from the emission surface 412b. A small amount of stray particles <NUM> (e.g., photons, ions, etc.) may undergo backscattering, leading to signal degradation and loss. The backscattered electrons may contact the second plurality of ribs 420b and/or emission surface 412b of the gain substrate layer <NUM>. Stray particles <NUM> that impinge on emission surface 412b may convert to stray electrons and corresponding stray holes. Thereafter, the free electrons may be emitted from emission surface 412b to contact the phosphor layer (see also, <FIG>). This may negatively impact recording and/or presentation of an image (e.g., as noise).

In an embodiment, anode <NUM> may include a phosphor screen to convert the amplified electrons (e-) <NUM> to photons. The input surface <NUM> of the phosphor/sensing layer <NUM> may be coated with a conducting material (not shown), such as chrome or some other suitable metal, to provide an electrical contact layer to receive the emitted electrons from emission surface 412b.

In another embodiment, anode <NUM> may comprise a conventional integrated circuit with a CMOS substrate and a plurality of collection wells, commonly used in image intensifier tubes. The electrons may be processed using signal processing equipment for CMOS sensors to produce an intensified image signal for display to the user.

<FIG> is a cross-sectional view of a portion of a semiconductor structure <NUM> corresponding to gain substrate layer <NUM>, for example, the gain substrate layer of <FIG>. Gain substrate layer <NUM> is doped to generate a plurality of electrons <NUM> for each free electron (e-) <NUM> that impinges on the input surface 412a of the gain substrate layer. In some cases, germanium may be added to the gain substrate layer <NUM>.

In some aspects, the thickness of the gain substrate layer may be about <NUM>-<NUM>, and the thickness of the gain substrate layer including both sets of ribs (T1) may be, without limitation, approximately <NUM>-<NUM>, wherein the first plurality of ribs 420a and the lower ribs 420b are included in the thickness. In some aspects, the thickness of the ribs may be about the same thickness as the gain substrate layer. Regions <NUM> and <NUM> correspond to vacuum or gap regions.

Gap distance (L1) is measured from the photocathode layer to the tip of ribs 420a and typically has a distance of about <NUM>-<NUM>. In some embodiments, the gap distance is about <NUM>. Gap distance (L2), the distance between the phosphor layer and the tip of the rib 420b, is in the range of about <NUM>-<NUM>. The height of ribs 420a does not need to be same as the height of ribs 420b. However, a rib from 420a is in vertical alignment with a rib from 420b, in order to minimize signal loss.

In an embodiment, the gain substrate layer may include first region <NUM> and second region <NUM>, which are configured (e.g., via doping) to direct the flow of electrons <NUM> to emission areas <NUM> of emission surface 412b. Emission areas <NUM> may be activated to a NEA state to facilitate electron flow from emission surface 412b.

The first region <NUM>, which is disposed adjacent to input surface 412a, may be doped to force electrons away from input surface 412a and into gain substrate layer <NUM>, thus inhibiting recombination of electron-hole pairs at input surface 412a. Inhibiting recombination of electron-hole pairs at input surface 412a ensures that more electrons flow through gain substrate layer <NUM> to emission surface 412b, thereby increasing efficiency. The first region <NUM> may be doped with a p-type dopant such as boron or aluminum, and may be relatively heavily doped (e.g., about <NUM><NUM> parts per cubic centimeter), approximately <NUM>-<NUM> deep. Other suitable dopants, concentrations, and dimensions for use with silicon semiconductors and other semiconductor materials, e.g., GaAs, will be readily apparent to those skilled in the art of semiconductor fabrication. In some aspects, the input surface 412a of the gain substrate layer <NUM> is coated with a conducting material (not shown), such as chrome, adjacent to the first region <NUM> to provide an electrical contact to the upper surface of the gain substrate layer <NUM>.

The second region <NUM> may be a moderately p-doped material, and may also be referred to herein as a background region. The second region may also comprise blocking structures <NUM> that are relatively heavily doped (e.g., <NUM><NUM> parts per cubic centimeter), e.g., with a p-type dopant such as boron or aluminum. The second region <NUM> (alone and/or in combination with first region <NUM>), may be referred to as an electron multiplier region.

Blocking structures <NUM>, disposed on the emission surface 412b, are doped (e.g., using P+ dopants) to repel electrons <NUM> to emission areas. Blocking structures <NUM> define blocking areas <NUM> of emission surface 412b, where electron flow into and out of gain substrate layer <NUM> is inhibited. Blocking areas <NUM> are regions at emission surface 412b that are effectively blocked by one or more of blocking structure <NUM>, shield <NUM> and dielectric film <NUM>. Blocking structures <NUM> may also help to maintain spatial fidelity, for example, by directing stray electrons (moving laterally) into the appropriate emission area <NUM>, helping to ensure that electrons <NUM> enter and exit gain substrate layer <NUM> along a vertical trajectory and do not cross into adjacent emission areas. Blocking structures <NUM> may have a height H of approximately <NUM>. The emission areas <NUM> may have a diameter of about <NUM>, with a <NUM> pitch between blocking structures <NUM>.

The blocking structures focus electrons to small areas, emission areas <NUM>, for emission. Additionally, focusing allows the electrons to travel greater distances. By funneling the electrons, the frequency of electrons that contact sidewalls of ribs is greatly reduced. This facilitates flow of the electrons to the phosphor layer without or with minimal signal loss.

Gain substrate layer <NUM> may further include shields <NUM>, which are doped to reduce and/or minimize effects of stray particles <NUM> (see, <FIG>). Shield <NUM> may be doped with an N-type dopant, e.g., by diffusion or implantation. In an embodiment, shield <NUM> is doped to encourage recombination of free electrons and free holes, thus, absorbing stray particles <NUM>. In some aspects, shield <NUM> may be disposed within gain substrate layer <NUM>, positioned at the base of the blocking structure <NUM>, proximal to the emission surface 412b. In some aspects, shields may be optional.

In other aspects, gain substrate layer may further include a dielectric film <NUM> disposed on emission surface 412b, positioned atop the base of the blocking structures <NUM>. A first surface of the dielectric film <NUM> may contact one end of ribs 420b and a second surface of the dielectric film may contact a surface of shield <NUM> at the emission surface 412b. In some aspects, dielectric film <NUM> may be optional.

Thus, shield <NUM> is disposed within a blocking structure <NUM>, wherein the surface of shield <NUM> is disposed at the emission surface 412b and the dielectric film <NUM> is disposed atop the emission surface 412b. Ribs 420b are disposed atop dielectric film <NUM>.

As mentioned previously, the distance between the photocathode and the tip of the ribs 420a may be reduced, allowing a lower voltage to be used. By decreasing this distance, a more compact and mechanically robust transmission mode image intensifier structure is provided allowing operation at lower voltages. Reduction of voltage and reduced rib spacings allow common wafer level fabrication processes to be used to make the image intensifier, and may lead to a reduction in the number of substrates.

Typically, the voltage will be set at a value suitable for extracting electrons from the photocathode and will provide enough energy to overcome the dead voltage of the gain layer to provide the desired gain. However, the voltage will be lower than a value which may lead to the generation of X-rays by the bombarding electrons. Thus, in some aspects, the upper limit is about 2000V and the lower limit is about 600V. The values may also depend upon the spacing between the tip of the ribs and the photocathode <NUM> (gap distance <NUM>).

Gap <NUM> may be provided between first region <NUM> and blocking structures <NUM>. Gap <NUM> may be sized or dimensioned such that the blocking structures do not interfere with the generation of electrons <NUM> at input surface 212a. This may provide the gain substrate layer with an effective electron multiplication area that equals or approaches <NUM>% of an area of input surface 212a. Crap <NUM> may be without limitation, approximately <NUM> to <NUM> or any other suitable distance in between. Other suitable dopants, concentrations, dimensions, and/or semiconductor materials, such as GaAs, may be used, as will be readily apparent to one skilled in the relevant art(s). The gain substrate layer <NUM> may generate several hundred electrons or more for each received electron. Accordingly, the number of electrons exiting the gain substrate layer <NUM> is significantly greater than the number of electrons that entered the gain substrate layer.

Still referring to <FIG>, regions between adjacent blocking structures <NUM> may form channels (see, <FIG>, channel <NUM>) that extend from input surface 212a to emission areas <NUM> of the emission layer 212b. The channels have relatively wide cross-sectional areas near input surface 212a, and relatively narrow cross-sectional areas towards emission areas <NUM>. The channels may act as funnels to direct electrons <NUM> to emission areas <NUM>, and are bounded by the blocking structures <NUM>. The channels may also be referred to herein as electron bombarded cells (EBCs). Semiconductor structure <NUM> may be configured with an array of EBCs, such as described below with reference to <FIG>. Semiconductor structure <NUM> is not, however, limited to the examples of any of <FIG>.

<FIG> shows an illustration of semiconductor structure <NUM>, which includes dielectric film <NUM>, including a first oxide layer <NUM> disposed on the emission surface 412b of a metal layer <NUM>, e.g., aluminum, disposed on the first oxide layer <NUM>, and a second oxide layer <NUM> disposed on the metal layer <NUM>. Shield <NUM> is shown, adjacent to emission surface 412b and within the blocking structure <NUM>. In some aspects, shield <NUM> is optional. In other aspects, dielectric film <NUM> is optional, and ribs 420b may be disposed at emission surface 412b, in contact with blocking structure <NUM> and or shield <NUM>.

In an exemplary embodiment, the layers of dielectric film <NUM> are fabricated using conventional fabrication techniques that are readily apparent to those of skill in the art. In one exemplary embodiment, the first oxide layer <NUM> is approximately <NUM>-<NUM> nanometers thick, the metal layer <NUM> is approximately <NUM>-<NUM> nanometers thick, and the second oxide layer <NUM> is approximately <NUM>-<NUM> nanometers thick. In accordance with this embodiment, the total thickness of dielectric film <NUM> is approximately <NUM>-<NUM> nanometers.

The layers of the illustrated dielectric film <NUM> perform a variety of functions in the exemplary embodiment. The first oxide layer <NUM> prohibits the emission of electrons from the emission surface 412b of the semiconductor structure <NUM> in areas where it is deposited (the blocked area <NUM>) thereby reducing any "dark current" by the ratio of area blocked by the first oxide layer <NUM> to the total area of the emission surface 412b. Dark current is the flow of electrons within a semiconductor structure produced by thermal variations, which creates random generation of electrons and holes, or noise, in the EBC.

In an exemplary embodiment, the metal layer <NUM> is biased to draw the increased number of electrons <NUM> toward it through the gain substrate layer. In the exemplary embodiment, the biasing is low, e.g., less than one volt, to prevent electrons from gaining enough energy to penetrate blocking structure <NUM> and to prevent damage to the gain substrate layer. In addition, the metal layer <NUM> acts as a blocking layer for light feedback in embodiments where a photoemitter or phosphor screen is used as a phosphor/sensing layer <NUM> (<FIG>). The metal layer <NUM> absorbs/reflects photons originating from such devices to prevent the photons from reaching the photocathode <NUM> through the emission surface 412b, thus reducing noise from light feedback from the phosphor/sensing layer <NUM>.

The second oxide layer <NUM> is disposed on the metal layer <NUM> to inhibit the emission of electrons by the metal layer <NUM>. Thus, noise attributable to the metal layer <NUM> is reduced. An individual rib of the plurality of ribs 420b is disposed on the second oxide layer <NUM>. The width of the rib may be less than, equal to, or greater than the width of the dielectric film <NUM>.

The illustrated emission areas <NUM> are geometric shapes (e.g., circles, squares, etc.) defined by the blocking structure <NUM>. The emission areas <NUM> may be essentially any suitable geometric shape. In an exemplary embodiment, the blocking structure <NUM> extends for about <NUM>-<NUM> between emission areas <NUM> and the emission areas <NUM> are about <NUM>-<NUM> in diameter.

<FIG> is a cross-sectional perspective view of semiconductor structure <NUM>, in which multiple rows of parallel and perpendicular blocking structures <NUM>, and associated ribs 420b form an array of emission areas <NUM>. Ribs are also present on the input surface 412a but are not shown. The ribs may be in a wall-type configuration (left) or as posts (right).

The individual EBCs form a matrix on semiconductor structure <NUM>. Each of the EBCs, and their associated emission areas <NUM>, correspond to regions of the input surface 412a such that the matrix of EBCs pixelate the electrons received at the input surface 412a of the gain substrate layer <NUM>. The number of EBCs actually employed in an array may be many more or less depending on the size of the individual EBCs and the desired resolution of the image intensifier.

<FIG> is another view of the example embodiment of <FIG>, in which shield <NUM> is illustrated. Ribs 420b are not shown, but are disposed as shown in <FIG>. In an embodiment, a width W1 of a base portion of blocking structures <NUM> is approximately <NUM>-<NUM>, and a width W2 of emission areas <NUM> is approximately <NUM> to <NUM>. In this example, the area excluding emission area <NUM> encompass more than <NUM>% of the emission surface 412b of semiconductor structure <NUM>. Semiconductor structure <NUM> is not, however, limited to these examples.

<FIG> depicts an expanded view of an EBC <NUM>, as shown in <FIG>. In an embodiment, emission area <NUM> has a width W<NUM> of approximately <NUM>. An exposed portion (e.g., ring) of blocking structure <NUM> extends a distance D of approximately <NUM> beyond emission area <NUM>. A rib 420b is disposed on the non-emission areas, and may have any suitable diameter between the inner dashed line and the outer dashed line.

In the examples of <FIG>, the gain substrate layer <NUM> is illustrated as a square array of EBCs. Gain substrate layer <NUM> may be configured with other geometric (e.g., circular, rectangular, or other polygonal shape), which may depend upon an application (e.g., circular for lens compatibility, or square/rectangular for integrated circuit compatibility). In an embodiment, to replicate a conventional micro-channel plate used in an image intensifier tube, a square array of <NUM>×<NUM> EBCs, or more, may be used. This may be useful, for example, to replicate a micro-channel plate of a conventional image intensifier tube.

In the example of <FIG>, semiconductor structure <NUM> is depicted as a <NUM>×<NUM> array of EBCs. Semiconductor structure <NUM> is not, however, limited to this example. The number of EBCs employed in an array may be more or less than in the foregoing example, and may depend on the size of the individual EBCs and/or a desired resolution of an image intensifier.

In the examples of <FIG>, emission areas <NUM> are depicted as having square shapes. Emission areas <NUM> are not, however, limited to square shapes. Emission areas <NUM> may, for example, be configured as circles and/or other geometric shape(s). Each EBC and associated emission area <NUM> corresponds to a region of input surface 412a (<FIG>), such that the array of EBCs pixelate electrons received at input surface 412a.

<FIG> is a flowchart of a method <NUM> showing operation of a mechanically robust transmission layer, and describes the example apparatus (MEMS image intensifier <NUM>) disclosed herein. Method <NUM> is not, however, limited to example apparatus disclosed herein.

At operation <NUM>, an electron is received at a gain substrate layer having an input surface with a plurality of ribs, such as described herein in one or more examples.

At operation <NUM>, for each received electron, a plurality of electrons is generated within the gain substrate layer, such as described in one or more examples herein.

At operation <NUM>, the plurality of electrons is repelled from blocking regions of the gain substrate layer that are doped to repel electrons, towards emissions areas of an emission surface having a second plurality of ribs, wherein ribs of the first plurality of ribs are aligned with ribs of the second plurality of ribs, such as described in one or more examples herein.

Support ribs combined with shaping of the incoming electrons and carriers within the transmission layer (gain substrate layer) can provide carrier registration and mechanical support in a transmission device. This structure has several advantages, including providing thin transmission layers, which minimizes signal loss. Additionally, other benefits include increased mechanical strength of the transmission layer, reduced gap distance (L1) spacing, and lower voltage operation. Further, by limiting complexity at least in part through reduction of the number of substrates, many common fabrication processes may be used with these techniques. These techniques provide for improving rigidity of the thin transmission layer (gain substrate layer) without degrading image quality.

The techniques disclosed herein may be implemented with/as passive devices (i.e., with little or no active circuitry or additional electrical connections). Techniques disclosed herein are compatible with conventional high temperature semiconductor processes and wafer scale processing, including conventional CMOS and wafer bonding processes, and a variety of fabrication processes.

In some aspects, support ribs present on upper or/and lower surfaces may be made of any material. Support ribs may be free-standing or connected to an adjacent substrate. Support ribs may be in any suitable configuration, including a grid of posts, or parallel lines/walls. The emission surface is less than the size of the input surface, to minimize lost carriers. Support ribs may be any suitable shape, including round, square, oval, etc. The upper and lower ribs are aligned with blocking structures to minimize or eliminate signal loss for the area consumed by the support ribs.

Claim 1:
An apparatus, comprising:
a semiconductor structure that includes:
a gain substrate layer doped to generate a plurality of electrons for each received electron that impinges on an input surface of the gain substrate layer;
a first plurality of ribs disposed at an input surface of the gain substrate layer;
a blocking structure disposed within the gain substrate layer that is doped to repel the plurality of electrons towards an emission area of an emission surface of the gain substrate layer;
a shielding region doped to absorb stray particles that impinge on the emission surface of the gain substrate layer, wherein the stray particles include one or more of stray photons and stray ions; and
a second plurality of ribs disposed at the emission surface of the gain substrate layer.