Session 1: Particle-based display technologies

Transcription

1 Session 1: Particle-based display technologies Ian Morrison Cabot Corporation The American Chemical Society 2005

2 HP Indigo press 3000 Performance: Up to color sheets/hour 800 x 800 dpi 180 lpi unique liquid HP Electroink HP s advantage includes our liquid ink-based printing technology ACS (C) 2005 Particle-based Display Technologies 2

3 Liquid ink-based printing technology Imaging Developing ACS (C) 2005 Particle-based Display Technologies 3

4 Particle based displays Reflective not emissive Adjusts with ambient light Thin, flexible, low power? The electronics is a real challenge. Require high resistivity so particles move, not ions therefore nonaqueous dispersions ACS (C) 2005 Particle-based Display Technologies 4

5 To create a display start with a print and invent ways to make it change: ACS (C) 2005 Particle-based Display Technologies 5

6 The Gyricon Display Charged, bichromal balls. Suspended in an oil. Encased in a plastic sheet. Addressed with electrodes. That Xerox built. ACS (C) 2005 Particle-based Display Technologies 6

7 Gyricon ball dynamics* (*Rick Lean, MIT) X E ψ θ Z Un-damped Under-damped Y Ground Electrode q Fluid Filled Cavity q d Bichromal Ball Critical-damped Over-damped Switching Electrode ACS (C) 2005 Particle-based Display Technologies 7

8 Suspended particle displays* Uncharged particles. Suspended in an oil. Transparent Addressed with electrodes. *Invented by E.H. Land in 1934 ACS (C) 2005 Particle-based Display Technologies 8

9 Electrophoretic displays Charged pigment particles. Suspended in a dyed oil. Addressed with electrodes. ACS (C) 2005 Particle-based Display Technologies 9

10 Problems with particle displays Sedimentation: Electrohydrodynamics: ACS (C) 2005 Particle-based Display Technologies 10

11 Shutter mode Charged pigment particles. Suspended in clear oil. Addressed with electrodes. ACS (C) 2005 Particle-based Display Technologies 11

12 A solution - encapsulation Solves Particle setting Electrohydrodynamic effects Light State Dark State Creates Self-spacing electrodes Coatable displays NOTE: These capsules are ~ 100 microns in diameter. ACS (C) 2005 Particle-based Display Technologies 12

13 Switching speed? use two different pigments Switching time goes as square of thickness: τ transit 2 d V µ The necessary thickness is determined by the optical density. Dye solutions have much lower optical density than pigments. Therefore dual pigments enables thinner. ACS (C) 2005 Particle-based Display Technologies 13

14 Dual particle displays E Ink ACS (C) 2005 Particle-based Display Technologies 14

15 Dual particle displays Negatively charged pigment particles. Positively charged pigment particles. Suspended in a clear oil. Addressed with electrodes. Sony s LIBRie EBR-1000EP from E Ink and Phillips Electronics ACS (C) 2005 Particle-based Display Technologies 15

16 E Ink electrophoretic display ACS (C) 2005 Particle-based Display Technologies 16

17 Dual particle displays ACS (C) 2005 Particle-based Display Technologies 17

18 Dispersions of oppositely charged particles ACS (C) 2005 Particle-based Display Technologies 18

19 How to image with flocculated particles The field necessary to separate charged particles is: separation Force Force Force Field = = q q q q total vdw elec n.b. The force varies with the product of particle charges, but the field also varies with the difference. Practical considerations set an upper limit of about 0.5 V/µm. A steric barrier is necessary to limit the maximum attractive force. ACS (C) 2005 Particle-based Display Technologies 19

20 Steric barrier necessary for typical pigments in oil For particle radii of 150 nm, zeta potentials of 52 mv and 52 mv (corresponding to 12 charges per particle!), the background conductivity of 50 ps/cm, and a Hamaker constant of 4.05x10-20 J. ACS (C) 2005 Particle-based Display Technologies 20

21 What about color? Color filter arrays Simple, but 2/3rds loss in brightness. ACS (C) 2005 Particle-based Display Technologies 21

22 Photoelectrophoretic displays Photosensitive pigments Light electric field produces change in charge Particles migrate in the field in or out of view Also a passive addressing scheme ACS (C) 2005 Particle-based Display Technologies 22

23 Color via plasmon resonance The magnitude, peak wavelength, and spectral bandwidth of the plasmon resonance associated with a nanoparticle are dependent on the particle s size, shape, and material composition, as well as the local environment. Silver nanoparticles Au and thin gold layers on silica. ACS (C) 2005 Particle-based Display Technologies 23

24 Plasmon resonance color depends on interparticle distance E Three color states when viewed from the top, depending on the electric field. E E=0 Blue Red Black ACS (C) 2005 Particle-based Display Technologies 24

25 Control of spacing with tethers Polymer tethers keep particles within 10 s of nanometers switching times are very short. Could be tethered to electrodes as well, etc. On Off ACS (C) 2005 Particle-based Display Technologies 25

26 Quantum effects Colloidal CdSe quantum dots dispersed in hexane. Quantum confinement effects allow quantum-dot color to be tuned with particle size. (Fluorescence shown.) Moungi Bawendi ACS (C) 2005 Particle-based Display Technologies 26

27 Q-dot optics also depend on interparticle distance Large Q-dots quench smaller Q-dots Q-dots can be coated with a dielectric and charged Q-dots could be tethered to each other or to an electrode. ACS (C) 2005 Particle-based Display Technologies 27

28 Electron injection into quantum dots Discoloration Coloration CdSe CdSe n.b. One electron per particle makes these 10 3 to 10 4 more sensitive than molecular electrochromics. ACS (C) 2005 Particle-based Display Technologies 28

29 Quantum dot electrochromic display Electrode Q Dot Layer Dielectric layer ITO on PE ACS (C) 2005 Particle-based Display Technologies 29