Flat FEA image sensor with HARP target

Abstract

In a new application of field emitter arrays (FEAs), a unique, ultrahigh-sensitivity, flat image sensor that consists of an FEA and a avalanche-mode photoconductive target is proposed.We have been working to develop highly sensitive camera tubes with a high-gain avalanche rushing amorphous photoconductor (HARP) target. Although our latest HARP tube is about 100 times as sensitive as a conventional solid-state image sensor, it suffers from drawbacks related to its length (about 100 mm) and power consumption. To overcome these problems and develop a next-generation, ultrahigh sensitivity, flat image sensor, we have developed an FEA image sensor.The configuration and operating principle of an FEA flat image sensor are shown in Fig. 1. The sensor consists of an FEA, a mesh electrode, and a HARP target, facing each other in close proximity. The FEA acts as an electron source and the mesh electrode accelerates electrons emitted from the field emitters and suppress their divergence. The HARP target converts incident light to electric charges and multiplies them through an intemal avalanche multiplication effect. A video signal is obtained, pixel-by -pixel, through the recombination of the two-dimensional charge (hole) pattem accumulated on the HARP target and the electrons emitted from the FEA. Figure 2 shows a prototype FEA image sensor. The prototype is only 10 mm thick and has 128 horizontal and 96 vertical pixels. Light output Spindt-type field emitters (a) Configuration (b) Operating principle Fig. 1 Configuration and operating principle of FEA image sensor with HARP target 0-7803-7256-5/02/$10.00 0 2002 IEEE 63

Fabrication of a Field Emitter Array with a Built-in Einzel Lens

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Vacuum, temperature, and time dependencies of field-emission current for RF-MEMS applications

“…The FE phenomenon can be mathematically described by the governing Fowler-Nordheim (F-N) [3][4][5][6][7] equation shown in (1). It expresses the FE current density J as a function of the external electric field F and the material work-function / ($4.5 eV for bare silicon).…”

“…Recent vacuum micro-electronics achievements [3,4] on the FE effect provide many research opportunities to RF engineers. Micro or nano-mechanical resonators have the advantages of high Q-factor, batch fabrication capabilities, and well-established MEMS processes.…”

Dependence of Thickness on Avalanche Characteristics of Te-Doped Amorphous Selenium Photoconductive Target

“…An amorphous selenium (a-Se) high-gain avalanche rushing amorphous photoconductor (HARP) target has been applied in imaging devices such as image pickup tubes, [1][2][3][4] field emitter array image sensors, 5,6) complementary metaloxide-semiconductor (CMOS) solid-state imagers, 7) and X-ray sensitive active matrix flat-panel imagers. 8) An ultrahigh-sensitivity New Super-HARP pickup tube using the avalanche effect has sensitivity of over 600 times greater than that of the SATICON pickup tube, 3) and it is about 100 times as sensitive as charge-coupled devices.…”