- 1. Principle of Thermal Electron Emission #6
- a. Conduction electrons confined in potential energy well in solids
- b. Electrons fill all energy states up to Fermi Energy at T=0K
- c. In vacuum, minimum energy to remove electron is work function
- d. Work function depends on material: metals (1eV to 5.6 eV)
- e. At high T, some e-'s have enough energy to eject #7
- f. Traditional cathode is hot filament of wire that "boils" off electrons
- g. 1 to 30 KV between cathode, grid, screen accelerates electrons (F = eE)
- 2. Raster Scan of Electron Beam in Traditional CRT
- a. Electric and magnetic fields sweep beam
- b. Screen coated with fluorescent phosphors (ZnS, ZnO, etc.)
- c. Phosphors excited by electrons emit R, G, or B light
- 1. Principle of Field-Emission
- a. Electric fields strongest where minimum radius of curvature #11
- b. Can microfabricate sharp pyramids with r ~ 200 Angstroms #12
- c. Tips placed ~1 um from grid; get high E-field (> 10^8 V/cm) at low V
- d. High electric fields distort potential energy well for electrons in tip
- e. Electrons at Fermi Energy can tunnel out in a vacuum (L ~ 10 Ang)
- f. These electrons are accelerated to grid and screen along the E-fields
- 2. Fowler-Nordheim Equation #12
- a. Classic relation showing emission current's dependencies
- b Typically, get 1-10 uA per pyramid with 140 V driving #12
- c. 99% of current into this device is delivered to the phosphors
- d. Maximize B with tip radius "r" and gate aperture "d"
- 1. IDEAL cathode since diamond naturally repels e-'s
- 2. Very low work function (0.2 to 0.3 eV)
- 3. Negative electron affinity and wide band gap #6
- 4. Donor e-'s need to have ~0.01 eV to eject (< KbT, 0.025 eV)
- 5. Hence, emits electrons at much lower E-fields than Si or metals
- 6. Simple, no need to microfabricate sharp tips
- 7. Can operate at higher pressures (1E-4 torr vs. 1E-7 torr)
- Main Outline
- III. Device Architecture
- Sources