Slide điện tử từ trường lecture 2 diodes

Lecture 02 Diodes 圖片來自;www.personeel.glr.nl/koster/elektro/diodes.JP Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt topics • • • • Semiconductor physics Diode forward characteristic Diode reverse characteristic Special diodes Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Solid-state material • Insulator (SiO2) – Strong covalent bonds, no free electron −8 −1 σ < 10 ( Ω − cm ) – Conductivity 1eV ≡ 1.6 ×10 −19 Joule – Energy gap Eg ≥ 3eV eV: eletron voltage • Semi-conductor (Si, Ge) – Conductivity 10 −8 < σ < 103 (Ω − cm) −1 – Energy gap < Eg < 3eV • Conductor (Cu, Ag) – Weak covalent bonds, many free electrons – Conductivity σ > 103 (Ω − cm) −1 – Energy gap Eg = 0eV Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Energy gap Energy level high energy Infinite many atoms Low energy conduction band Energy-level gap valance band http://oldsite.vislab.usyd.edu.au/photonics/devices/semicdev/doping2.html One atom Level : high energy Level : low energy electrons conduction band conduction band conduction band Energy gap overlap valance band Energy-level gap valance band Energy-level gap valance band Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Famous Semi-conductors • Element semi-conductor – Si • Cheap • Energy gap > Ge ặ small leakage current ã Stable oxide Ge • First transistor • Small energy gap • Unstable oxide • Compound semi-conductor – GaAs Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Intrinsic semiconductor (silicon) At very low temperature ion http://oldsite.vislab.usyd.edu.au/photonics/devices/semicdev/doping2.html Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Intrinsic semiconductor at room temperature Mass-action law: n = p = ni ⇒ np = ni2 − KTG ni = BT e E For silicon semi-conductor Material parameter B = 5.4 ×1031 EG = 1.12eV Boltzmann’s constant k = 8.62 × 10 −5 eV K At room temperature Free electrons and holes generated by thermal ionization, so the concentration is same n = p = ni T ≈ 300 K ni ≈ 1.45 ×1010 carriers Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com cm3 https://fb.com/tailieudientucntt Hole and electrons moving drift Drift velocity v = μE Resistivity R=ρ l E= E : electric field strength (V/cm) μ : mobility of hole/electron (cm2/V-sec) l A Charge density ρ ≡ nq ( Ω − cm ) conductivity A e e J = σE J n = qnμ n E J drift = q ( pμ p + nμ n ) E e Nq Nqv = T L I Nqv J= ⇒J= A AL N n≡ ⇒ J = nqv LA I≡ σ ≡ nq μ J p = qpμ p E f q For intrinsic silicon : cm μ p = 480 V ⋅s cm μ n = 1350 Electron density V ⋅s Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt diffusion For intrinsic silicon : q = 1.6 × 10 C cm D p = 12 J : current density s q : electron charge cm Dn = 34 D : diffusivity of hole/electron s −19 dp J p = −qD p dx dn J n = qDn dx p n electron diffusion hole diffusion Jp Jn x x The conventional current direction is the positive charge flow direction 10 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt PN Junction reverse bias IS > ID IS − ID = I q J = q N = qN DWn A N AND qJ = q AWdep N A + ND Wdep = Wn + W p = Cj = Junction capacitance dq J Cj = dVR ⇒ Cj = VR =VQ εs A VR = C jo = A 2ε s 1 ( + )(V0 + VR ) q N A ND C jo varactor + VVRo qε s N A N D ( ) N A + N D V0 Wdep 23 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt 圖片來自;www.rvweb.fr/ /electricite/partie3_4.php 24 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Minority carriers distribution in forward bias (the story about reverse saturation current) electrons p1 = p2 e V21 VT page18 → p n ( xn ) = p n e V VT holes pn ( x) = pn + [ pn ( xn ) − pn ]e Q J p = − qDP ⇒ Jp = q Dp Lp − ( x − xn ) LP dp dx pn (e V VT − 1)e − ( x − xn ) LP Total loss by recombination = External electric field inject electrons Inject holes from P region to diffuse away from the junction into the N region and disappear by recombination 25 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt PN Junction under forward bias Jp = q Dp Lp pno (e V VT − 1) V Dn Jn = q n po (e VT − 1) Ln I = A( J p + J n ) IS < ID Reverse saturation current I = I s (e V / VT if Dp V Dn I = Aqn ( + )(e V T − 1) L p N A Ln N D i − 1) V > I s Forward ⇒ i ≈ I se v nVT i ⇒ v = nVT ln Is V1 I1 ≈ I s e nVT V2 I ≈ I se nVT n : Ideality factor which depending on diode’s material and physical structure ⎧1 ⎪ n = ⎨1 ⎪2 ⎩ Ge Si( I D ≥ 25mA) Si( I D ≤ 25mA) I2 I2 ⇒ V2 − V1 = nVT ln = 2.3nVT log I1 I1 28 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt VD = ⇒ I D = Open current Forward bias VD > ⇒ I D ≈ I s e reverse bias VD < ⇒ I D = − I s VD nVT Cut-in voltage V r Vr = 0.7 → Vr = 0.25 → Si Ge Vr = 1.2 → GaAs 29 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Diode Model I (ideal model ) 30 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Diode Model II (constant-Voltage Drop model ) 31 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Diode Model III (Piecewise-linear model ) 32 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Table 3.1 Modeling the Diode Forward Characteristic 33 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Special Diodes (Zener Diode) 圖片來自;www.alibaba.com/catalog/11418809/0_5w_Series 34 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt I = Iz + IL ⇒ V − Vz Pz Vz = + R Vz RL I = I z (max) + I L (min) V − Vz Pz (max) Vz ⇒ = + R Vz RL (max) I = I z (min) + I L (max) V − Vz Pz (min) Vz ⇒ = + R Vz RL (min) Ideal case: rz = RL ↑ (max) → I L ↓Q R = K ∴ I = fixed ⇒ I z ↑ (max) RL ↓ (min) → I L ↑Q R = K ∴ I = fixed ⇒ I z ↓ (min) 35 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt hyperphysics.phy-astr.gsu.edu/ /schottky.gif The others Special Diodes Schottky Diode - Metal + semiconductor (unipolar) Light emitting diode (LED) - GaAs diode - GaN diode (B, G) Tunnel diode Photo diode (PD) Opto coupler (LED + PD) www.personeel.glr.nl/koster/elektro/ledjes.JPG hyperphysics.phy-astr.gsu.edu/ /tundio.html home.swipnet.se/ /hifi_100pr/photodiode.jpg www.du.edu/~etuttle/electron/circ43.gif www.geda.seul.org/ /analog/photodiode-1_tn.png 36 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt LED • 1963 Red • 1993 Blue • 1996 white 37 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt ... ⇒E= p1 p2 V1 V2 ∫ dV = ∫ − VT dp p p1 → V2 − V1 = −VT (ln p2 − ln p1 ) = VT ln p2 V21 Boltzmann equation Mass-action law VT ⇒ p1 = p2 e J n = ⇒ n1 = n2 e Vo =V 21 = VT ln −V21 VT p1 p2 N AND Vo... temperature (20 oC)VT kT VT ≡ q k = 1.38 × 10 VT thermal voltage 溫度伏特當量 ≈ 25 mV Boltzmann’s constant − 23 joules kelvin T = 27 3+ oC T = 20 o C → 29 3o K ⇒ VT ≈ 25 mV T = 27 o C → 300o K ⇒ VT ≈ 26 mV q =... V2 I ≈ I se nVT n : Ideality factor which depending on diode’s material and physical structure ⎧1 ⎪ n = ⎨1 ? ?2 ⎩ Ge Si( I D ≥ 25 mA) Si( I D ≤ 25 mA) I2 I2 ⇒ V2 − V1 = nVT ln = 2. 3nVT log I1 I1 28