1 / 11

Lecture #33

OUTLINE The MOS Capacitor: C-V examples Impact of oxide charges Reading: Chapter 18.1, 18.2. Lecture #33. C. QS. C ox. HF-Capacitor. V G. V T. V FB. Examples: C - V Characteristics. Does the QS or the HF-capacitor C-V characteristic apply? MOS capacitor, f=10kHz.

roary-diaz
Download Presentation

Lecture #33

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. OUTLINE The MOS Capacitor: C-V examples Impact of oxide charges Reading: Chapter 18.1, 18.2 Lecture #33 EE130 Lecture 33, Slide 1

  2. C QS Cox HF-Capacitor VG VT VFB Examples: C-V Characteristics • Does the QS or the HF-capacitor C-V characteristic apply? • MOS capacitor, f=10kHz. • MOS transistor, f=1MHz. • MOS capacitor, slow VG ramp. • MOS transistor, slow VG ramp. EE130 Lecture 33, Slide 2

  3. Example: Effect of Doping C/Cox • How would C-V characteristic change if substrate doping NA were increased? • VFB • VT • Cmin 1 VG VT VFB EE130 Lecture 33, Slide 3

  4. Example: Effect of Oxide Thickness C/Cox • How would C-V characteristic change if oxide thickness xo were decreased? • VFB • VT • Cmin 1 VG VT VFB EE130 Lecture 33, Slide 4

  5. In the oxide: Trapped charge Qot High-energy electrons and/or holes injected into oxide Mobile charge QM Alkali-metal ions, which have sufficient mobility to drift in oxide under an applied electric field At the interface: Fixed charge QF Excess Si (?) Trapped charge QIT Dangling bonds Oxide Charges In real MOS devices, there is always some charge in the oxide and at the Si/oxide interface. EE130 Lecture 33, Slide 5

  6. In general, charges in the oxide cause a shift in the gate voltage required to reach the threshold condition: (x defined to be 0 at metal-oxide interface) In addition, they may alter the field-effect mobility of mobile carriers (in a MOSFET) due to Coulombic scattering Effect of Oxide Charges EE130 Lecture 33, Slide 6

  7. Fixed Oxide Charge QF M O S qQF / Cox 3.1 eV Ec= EFM |qVFB| Ev Ec EFS Ev 4.8 eV EE130 Lecture 33, Slide 7

  8. Parameter Extraction from C-V From a single C-V measurement, we can extract much information about the MOS device. • Suppose we know that the gate-electrode material is heavily doped n-type poly-Si (FM=4.05eV), and that the gate dielectric is SiO2 (er=3.9): • From Cmax = Cox we determine the oxide thickness xo • From Cmin and Cox we determine substrate doping (by iteration) • From substrate doping and Cox we calculate the flat-band capacitance CFB • From the C-V curve, we can find • From FM, FS, Cox, and VFB we can determine Qf EE130 Lecture 33, Slide 8

  9. Determination of FM and QF Measure C-V characteristics of capacitors with different oxide thicknesses. Plot VFB as a function of xo: V FB 10nm 20nm 30nm xo 0 –0.15V ´ ´ –0.3V ´ EE130 Lecture 33, Slide 9

  10. Odd shifts in C-V characteristics were once a mystery: Source of problem: Mobile charge moving to/away from interface, changing charge centroid Mobile Ions EE130 Lecture 33, Slide 10

  11. Interface Traps Traps cause “sloppy” C-V and also greatly degrade mobility in channel EE130 Lecture 33, Slide 11

More Related