Chapter 10 : Diodes

M3-1: IC Devices A Portion of the Periodic Table

Single Crystal Silicon

•Reduction of silica (sand) to metallurgical grade silicon (MGS) with a purity of about 98% (Al,Fe) by heating silica with carbon ; SiO 2(solid) +2C (solid)--  Si (solid) +2CO (gas) •Converting MGS to trichlorosilane (SiHCl 3 ); Si(solid)+3HCl(gas) -  SiHCl 3 (liquid)+H 2 (gas) •Purification of trichlorosilane by distillation; •Chemical vapor deposition of silicon from purified SiHCl 3 to obtain electronic grade polysilicon (EGS) which has a very low impurity level of 10 13 /cm 3 .

2 SiHCl 3 (gas) + 2H 2 (gas) -  2Si(solid) +6HCl •Czochralski (CZ) crystal growth to obtain single crystal silicon

Moore’s First Law

Moore’s First Law

Different Integration Levels in the IC Industry

Integration level Small scale integration (SSI) Time 1960-1965 Medium scale integration (MSI) 1965-1975 Large scale integration (LSI) 1975-1985 1985-1995 Very large scale integration (VLSI) Ultra large scale integration (ULSI) 1995- present Number of devices/chip 2-100 100- 10,000 10,000- 500,000 500,000- 5,000,000 > 5,000,000

N-type silicon is created by adding valence five impurities

P-type silicon is created by adding valence five impurities

Shockley equation

Exercise 10-1

Load-line analysis of diode circuits

Example 10.1 : Load analysis

Example 10-2 : Load line analysis

Load line is formed to find the operating point - Current and voltage can be determined once the operating point is known .

Example 10-4 . Analysis of a Zener-diode regulator with a load Find the load voltage v L and source current I S if v SS = 24 V, R= 1.2 k Ώ and R L = 6 k Ώ .

Example 10-5 . Analysis by assumed diode states

10-6 Rectifier Circuits (from ac power to dc power) Half- wave rectifier circuits  the source voltage – 0.7 V = the output voltage  When the source voltage is negative, diode is reversed- biased, no current flows through the load .

Battery charging circuit  Current flows when the ac source voltage is higher than the battey voltage  R is to limit the magnitude of the current .

 When ac source voltage is less than the battery voltage, the diode is reverse biased and the current is 0  The current only flows in the direction that charges the battery .

 To convert an ac voltage into a nearly constant dc voltage Place a large capacitance across the output terminals.

When the ac source reaches a positive peak, the capacitor is charged to the peak voltage

I L : average load current; T : period of the ac voltage A small ripple : due charge and discharge cycle V r : peak-to-peak ripple voltage

Full-wave rectifier circuits

Full-wave rectifier circuits  The capacitor discharges for only a half-cycle before being recharged .  Capacitance is only half of that in the half-wave circuit . C= I L T/2 V r  When ac votage >0, current flows through A, load then returns through B.  When ac voltage <0, current flows through C and D .

Clipper circuits  Clips off any part of the input waveform above 6 V and less than – 9V .

 Both diodes are off , therefore no currents flow when the input voltage is between -9 and 6 V .

 v in > 6V, diode A is ON , v 0(t) = 6 V , because the diode connects 6V battery to the output terminals .

 v in <- 9 V, v 0(t) = - 9V (diode B connects to the battery).  R is large enough so that the forward diode current is within reasonable bounds (few milliamps); but small enough for a negligible voltage drop in the reverse diode current .

 Zener diode can substitute the battery (don’t have to change frequently)

Clipper circuits (cont’d) v in > 6V, diode A is ON , v 0(t) = 6 V , because the diode connects 6V battery to the output terminals .

v in <- 9 V, v 0(t) = - 9V (diode B connects to the battery).

Clipper circuits (cont’d)

Another Example 0.6 V forward voltage drop for the diodes (a) Sketch the transfer characteristic (b) Sketch the output waveform if v in (t) = 15 sin ( ωt)

Another example 0.6 V forward voltage drop (a) Sketch the transfer characteristic (b) Sketch the output waveform if v in (t) = 15 sin ( ωt)

Example 0.6 V forward voltage drop for the diodes (a) Sketch the transfer characteristic

Example 0.6 V forward voltage drop for the diodes (a) Sketch the transfer characteristic