Lecture 07 Metal-Oxide-semiconductor Field-EffectTransistors (MOSFETs) 圖片來自casemods.pointofnoreturn.org/pwm/mosfets.html Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt topics • FET’s physical operation • MOSFET’s current-voltage characteristic Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Why FET ? • • • • Small size (5% BJT) Little operation power Simple Manufacturing process Easy to implement VLSI Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt • MESFET • JFET Classification – Depletion • N-channel • P-channel • MOSFET – Depletion • NMOS • PMOS • CMOS – Enhancement • NMOS • PMOS • CMOS CuuDuongThanCong.com Microelectronic Circuit by meiling CHEN https://fb.com/tailieudientucntt Structure of JFET (n-channel) gate P-type source P-type depletion drain N-type depletion P-type + VGS − − VDS + VGS = ⇒ I ≡ I DSS Reverse VGS ↗ Ỉdepletion region ↗Ỉchannel ↘ỈI↘ Reverse VGS ↗↗Ỉ depletion region ↗↗Ỉchannel ~0 ỈI=0 (pinch off) Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt symbol of JFET D D G G S N-channel S P-channel Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Structure of depletion-type MOSFET (n-channel) VGS = 0V I DSS electrons Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt depletion-type MOSFET (n-channel) VGS = −V ++++++ Depletion Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt symbol of depletion-type MOSFET NMOS Current direction PMOS Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Structure of enhancement-type NMOS transistor insulator 1010 ~ 1015 Ω L = 0.1 ~ 3μm tox = ~ 50nm W = 0.2 ~ 100 μm 10 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Ohmic region RDS ↓ iD VGS > Vt VDS ↑⇒ I D ↑ RDS ↑ Resistance characteristic 15 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt large VDS Pinch-off VDS = max VDS = iD 16 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Pinch-off 17 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Total capacitance at dx Q = CV ⇒ dq = −CoxWdx[v GS −v( x) − Vt ] n − electrons Cox : capacitance per unit gate area 18 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt dq dq dx = dt dx dt dq = −CoxWdx[vGS − v( x) − Vt ] i= dx dv( x) = − μ n E ( x) = μ n dt dx dv( x) dx dv( x) iD = i = μ n CoxW [vGS − v( x) − Vt ] dx iD dx = μ n CoxW [vGS − v( x) − Vt ]dv( x) ⇒ i = μ n CoxW [vGS − v( x) − Vt ] ∫ L iD dx = ∫ v DS μ nCoxW [vGS − v( x) − Vt ]dv( x) W [(vGS − Vt )vDS − vDS ] Ohmic L = vGS − Vt Saturation region iD = μ nCox ∴ vDS region W [(vGS − Vt ) − (vGS − Vt ) ] L W iD = μ nCox (vGS − Vt ) Saturation region L ⇒ iD = μ nCox 19 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Structure of enhancement-type CMOS transistor 20 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt EMOSFET operation mode • • • Ohmic (triode) region Saturation region Cutoff region vDS ≤ vGS − Vt vSD ≤ vSG − Vt vDS ≥ vGS − Vt vSD ≥ vSG − Vt vGS ≤ Vt > vSG ≤ Vt , Vt < + + − + − − 21 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt NMOSFET current-Voltage characteristic Ohmic region ID = μ n Co w 2L [2(vGS − Vt )vDS − vDS ] ID = μ n Co w 2L (vGS − Vt ) Cutoff region 22 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt 圖片來自en.wikipedia.org/wiki/MOSFET 23 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt 24 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt ID = μ n Co w 2L (vGS − Vt ) Saturation region large-signal model 25 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Channel length modulation (as Early effect) 26 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt 27 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt 28 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt 29 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt ... Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt Pinch-off 17 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt... Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt 27 Microelectronic Circuit by meiling CHEN CuuDuongThanCong.com https://fb.com/tailieudientucntt