1 / 7

Charge coupled devices and memories

Charge coupled devices and memories. Charge coupled devices Imaging applications, delay line in signal processing, filters etc. Uses MOS-C Semiconductor Memories Dynamic random access memories (DRAMs) use MOS-C in deep depletion inversion as storage units.

yagil
Download Presentation

Charge coupled devices and memories

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Charge coupled devices and memories • Charge coupled devices • Imaging applications, delay line in signal processing, filters etc. • Uses MOS-C • Semiconductor Memories • Dynamic random access memories (DRAMs) use MOS-C in deep depletion inversion as storage units. • We will qualitatively discuss the operation of these devices.

  2. M O S M O S p-Si p-Si VG < 0 VG > 0 Accumulation of holes W QM Depletion of holes MOS-capacitor - review Consider ideal case, with p-type Si VG < 0 accumulation VG > 0; depletion, but less than VT

  3. M O S M O S p-Si p-Si VG>>0 VG>>0 WT QM Depletion of holes Inversion electrons MOS-capacitor - review VG >> 0; VG > VT Steady state inversion condition Depletion layer = WT VG >> 0; VG > VT applied instantaneously. W is larger than WT. W QM After a few ms, you get steady-state condition, and W reduces to WT. Inversion layer forms Depletion of holes

  4. Time required to form inversion layer • It take a few milli-seconds to form the inversion layer since they are caused by minority carriers. Depends on e-h generation rate • can generate faster by optical means • can generate by injection of electrons from n+source and drain if present in close proximity • can increase the temperature to increase e-h generation rate or by introducing deep levels. • In CCDs, e-h pairs are generated by optical means, and generation by thermal means must be kept to a minimum (Why?)

  5. CCD operation region oxide electrons depletion VT Concept of CCD imager • Generation in depletion layer  light intensity • i.e., inversion layer charge  light intensity • Read out of charge pulse amplitude by operating as shift registers • Need to read out sequentially fast enough such that the thermal generation of carriers can be neglected. • 3- clock provides directionality. CG Al VG

  6. Memories • Logic devices that store and manipulate information. • Random access and sequential access. • Semiconductor Memories • non-volatile memory • ROM, PROM, EPROM, E2PROM • Volatile memories • DRAM - need to refresh every few ms. • SRAM - no need to refresh • One transistor DRAM cell • high density, but requires complex read/write/refresh circuits.

  7. One transistor DRAM cell Column bit or data line (BL) Row Word line (WL) CS VP A stored one will be deep depletion condition. A stored zero will be the inversion condition. Note that a stored one will revert to zero if not refreshed. Need refreshing every few milliseconds.

More Related