0. Semiconductor Devices & HVIC
1. POWER MOSFETs
2. INSULATED GATE BIPOLAR TRANSISTORS
3. FAST RECOVERY DIODE
4. HIGH VOLTAGE ICs
/부품 연구소
최 동 찬 (EastChan)
Power Part

1. • Construction of power MOSFETs • Physical operations of MOSFETs
Outline
• Construction of power MOSFETs
• Physical operations of MOSFETs
• Power MOSFET switching Characteristics
• Factors limiting operating specifications of MOSFET
이기는 경영! 악착같이,될때까지,끝까지!
1/47 2

2. GND Multi-cell Vertical Diffused Power MOSFET (VDMOS) 2/47
이기는 경영! 악착같이,될때까지,끝까지!
2/47 2

3. Basic structure of the HEXFET2
이기는 경영! 악착같이,될때까지,끝까지!
3/47

4. GND Important Structural Features of VDMOS accumulation layer
1. Parasitic npn BJT. Held in cutoff by body-source short
2. Integral anti-parallel pn diode.
3. Extension of gate metallization over drain drift region.
→ Field plate and accumulation layer functions.
4. Division of source into many small areas connected electrically in parallel.
Maximizes gate width-to-channel length ratio in order to increase gain.
5. Lightly doped drain drift region. Determines blocking voltage rating.
이기는 경영! 악착같이,될때까지,끝까지!
4/47

5. MOSFET I-V Characteristics
Cutoff - The drain-source voltage to avoid breakdown voltage BVDSS must be larger than the applied drain-source voltage to avid breakdown and the attendant high power dissipation.
Ohmic - The power dissipation can be kept within reasonable bounds by minimizing VDS(ON) even if the drain current is fairly large.
Active - The drain current is independent of the VDS & depends on only on the Vgs.
이기는 경영! 악착같이,될때까지,끝까지!
5/47

6. Example : Datasheet of FQA62N25C (250V N-Channel MOSFET)
이기는 경영! 악착같이,될때까지,끝까지!
6/47

7. The Field Effect - Basis of MOSFET Operation ( VGG1 < VGG2 < VGG3 )
• When a small positive gate-source voltage is applied to the capacitor structure.
- The positive charge & equal negative charge are the both side of the gate oxide.
- Repel the majority-carrier holes , thus exposes the negatively charged acceptor, thus creating a depletion region.
• Further increases in Vgs :
- The depletion layer to grow in thickness & additional negative charge.
- Begins to attract free electrons as well as repelling free holes.
- Electron-hole generation.
• The layer of free electrons at the interface will be highly conducting and will have all the properties of an n-type semiconductor.
→ inversion layer : conductive path & channel between n+ drain and source .
• The threshold voltage is inversely proportional to
- Oxide capacitance per unit area tox = oxide thickness
이기는 경영! 악착같이,될때까지,끝까지!
7/47

8. MOSFET Capacitances Determining Switching Speed
• Gate-source capacitance Cgs approximately constant and independent of applied voltages.
• Gate-drain capacitance Cgd varies with applied voltage.
Variation due to growth of depletion layer thickness until inversion layer is formed.
• Drain-source capacitance Cds doesn’t materially affect any of the switching characteristics or waveforms.
이기는 경영! 악착같이,될때까지,끝까지!
8/47

9. Equivalent circuit & MOSFET Capacitances Determining Switching Speed
That the capacitance Cgs ,Cgd & Cds are not constant but vary with the voltage across them because part of the capacitance is contributed by depletion layers.
• The most Significant change in capacitance occurs in Cgd because the voltage change across it, vds, is much larger than the voltage change across Cgs.
• For approximate calculations of switching waveform
- Cgd is approximated by the two discrete values Cgd1 & Cgd2 with the change in value occurring at vds=vgs where the MOSFET is either entering or leaving the ohmic region
- The gate-source capacitance will be assumed to be constant.
이기는 경영! 악착같이,될때까지,끝까지!
9/47

10. Example : Datasheet of FQA62N25C (250V N-Channel MOSFET)
이기는 경영! 악착같이,될때까지,끝까지!
10/47

11. A MOSFET being turned on by a driver in a clamped inductive load
The gate-source capacitance Cgs is total value of capacitance that needs to be first charged to a critical threshold voltage level Vgs(th), before drain current can begin to flow.
The gate-drain capacitance Cgd (‘miller’ capacitance) between the gate electrode and the N-drift drain region contributes most to the switching speed limitation of the MOSFETs.
The rate of rise of voltage, Vgs, over Gate and Source terminals of the MOSFET is governed by value of the total resistance in series (Rdr+RGext+RGint) and total effective value of capacitance (Cgs+Cgd).
Rgext is the resistance one generally puts in series with the Gate of a MOSFET to control the turn-on and turn-off speed of the MOSFET.
이기는 경영! 악착같이,될때까지,끝까지!
11/47

12. A MOSFET being turned on by a driver in a clamped inductive load
• Free-wheeling diode assumed to be ideal. (no reverse recovery current).
이기는 경영! 악착같이,될때까지,끝까지!
12/47

13. A MOSFET being turned on by a driver in a clamped inductive load
• Free-wheeling diode assumed to be ideal. (no reverse recovery current).
이기는 경영! 악착같이,될때까지,끝까지!
13/47

14. A MOSFET being turned off by a driver in a clamped inductive load
• Assume ideal freewheeling diode.
• Essentially the inverse of the turn-on process.
• Model qualitatively using the same equivalent circuits as for turn-on. Simply use correct driving voltages and initial conditions
이기는 경영! 악착같이,될때까지,끝까지!
14/47

15. dV/dt Limits to Prevent Parasitic BJT Turn-on
• The parasitic BJT might be turned on by a fast-rising drain-source voltage (10,000V/μs).
- Down the switching speed (∵ large RG)
- Smaller values of turn-off gate drive.
• For mechanism of possible destruction of MOSFETs used in a bridge configuration :
- Prevented using diodes DL+ and DL- instead of directly connecting freewheeling diode Df+ and Df- to the MOSFET drains.
이기는 경영! 악착같이,될때까지,끝까지!
15/47

16. Example : Datasheet of FQA62N25C (250V N-Channel MOSFET)
Maximum Gate-Source Voltage
• VGS(max) = maximum permissible gate-source voltage.
• If VGS >VGS(max) rupture of gate oxide by large electric fields possible.
• Gate oxide typically 1000 anstroms thick
• Typical VGS(max) : V
• Static charge on gate conductor can rupture gate oxide
• Handle MOSFETs with care (ground yourself before handling device)
• Place anti-parallel connected Zener diodes between gate and source as a protective measure.
Example : Datasheet of FQA62N25C (250V N-Channel MOSFET)
이기는 경영! 악착같이,될때까지,끝까지!
16/47

17. MOSFET Breakdown Voltage
• BVDSS = drain-source breakdown voltage with VGS = 0
• Achieve large values by
1. Avoidance of drain-source reach through by heavy doping of body and light doping of drain drift region
2. Appropriate length of drain drift region
3. Field plate action of gate conductor overlap of drain region
4. Prevent turn-on of parasitic BJT with body-source short .
이기는 경영! 악착같이,될때까지,끝까지!
17/47

18. Example : Datasheet of FQA62N25C (250V N-Channel MOSFET)
이기는 경영! 악착같이,될때까지,끝까지!
18/47

19. MOSFET On-state Losses
• On-state power dissipation Pon = Io2 rDS(on)
• Large VGS minimizes accumulation layer resistance and channel resistance
• rDS(on) dominated by drain drift resistance for BVDSS > few 100 V
• rDS(on) =
• rDS(on) increases as temperature increases.
Due to decrease in carrier mobility with increasing temperature.
이기는 경영! 악착같이,될때까지,끝까지!
19/47

20. Example : Datasheet of FQA62N25C (250V N-Channel MOSFET)
이기는 경영! 악착같이,될때까지,끝까지!
20/47

21. • Construction and I-V characteristics • Physical operation
Insulated Gate Bipolar Transistors (IGBTs)
Outline
• Construction and I-V characteristics
• Physical operation
• Switching characteristics
이기는 경영! 악착같이,될때까지,끝까지!
21/47

22. Insulated Gate Bipolar Transistors (IGBTs)
Switching speed, peak current capability, ease of drive, wide SOA, avalanche and dv/dt capability have made power MOSFETs.
Their conduction characteristics which are strongly dependent on temperature and voltage rating.
The voltage rating goes up, the inherent reverse diode displays increasing Qrr and Trr which leads to increasing switching losses.
The absence of the integral reverse diode gives the user the flexibility of choosing an external fast recovery diode to match a specific requirement or to purchase a “co-pak”.
The lack of an integral diode can be an advantage or a disadvantage, depending on the frequency of operation, cost of diodes, current requirement.
The additional turn-on losses in the IGBT due to the reverse recovery of the freewheeling diode.
이기는 경영! 악착같이,될때까지,끝까지!
22/47

23. Perspective view of an IGBT
이기는 경영! 악착같이,될때까지,끝까지!
23/47

24. Vertical cross section of an IGBT
• Cell structure similar to power MOSFET (VDMOS) cell.
• P-region at collector end unique feature of IGBT compared to MOSFET.
• Punch-through (PT) IGBT - N+ buffer layer present.
• Junction labled J1 is the reverse-blocking junction
• Junction labled J2 is the forward-blocking junction
이기는 경영! 악착같이,될때까지,끝까지!
24/47

25. The IGBT current-voltage charactoristics
Device Symbol
• The characteristics of an n-channel IGBT apears similar to those of a logic-level BJT.
이기는 경영! 악착같이,될때까지,끝까지!
25/47

26. The on-state current flow paths
On-state Operation
The gate drive circuit controls directly the MOSFET channel of the IGBT and, through the drain current of the MOSFET, the base current of its bipolar portion.
By its MOSFET portion, the turn-on losses will be significantly affected by the gate drive impedance.
Notice the turn-off delay of the current waveform during the Miller effect.
The on-state current flow paths
An increase in gate drive impedance prolongs the Miller effect and causes a delay in the current fall time that is similar to a storage time.
The impact of the gate drive impedance on total switching losses depends on the basic design of the IGBT and its speed.
The faster the IGBT the greater its sensitivity to the gate drive impedance.
이기는 경영! 악착같이,될때까지,끝까지!
26/47

27. Forward-bias voltage drop across pn junction = 0.7V
Equivalent circuit for the IGBT
The effective MOSFET and BJT operating portions of the structure
Equivalent circuit showing the transistors comprising the parasitic thyristor
Approximate equivalent circuit
Forward-bias voltage drop across pn junction = 0.7V
이기는 경영! 악착같이,될때까지,끝까지!
27/47

28. Switching caracteristics –Turn-on Transient
The Turn-on portions of the waveforms appear similar to those of the power MOSFET
The gate-drain capacitance Cgd will increase in the MOSFET portion of the IGBT at low drain-source voltage in a manner similar to that observed with power MOSFETs.
The pnp transistor portion of IGBT traveses the active region to its on state more slowly than the MOSFET portion of the IGBT.
Until the pnp transistor is full on, the full benefit of conductivity modulation of the drain-drift region has not been achieved.
이기는 경영! 악착같이,될때까지,끝까지!
28/47

29. Switching caracteristics –Turn-off Transient
Major different :
Turn-off is observed in the drain current waveform where there are two dstinct time intervals.
The “tailing” of the drain current during the second interval tfi2 is due to the stored charge in the n- drift region.
The “tailing” of the drain current
Punch-through IGBTs attempt to minimize the current tailing problem by shortening the duration of the tailing time.
Tailing current
이기는 경영! 악착같이,될때까지,끝까지!
29/47

30. • Basic structure and I-V characteristics • Switching waveforms
Fast recovery diode
Outline
• Basic structure and I-V characteristics
• Switching waveforms
• Reverse recovery
이기는 경영! 악착같이,될때까지,끝까지!
30/47

31. Basic structure and I-V characteristics
The n- layer , which is often termed the drift region, is the prime structural feature not found in low-power diodes.
The drift region establishes what the reverse breakdown voltage will be.
The reverse bias portion of the characteristic shows avalanche breakdown at BVBD.
The exponential i-v relationship in forward bias expected from signal-level diode.
Characteristics is masked by the ohmic resistance RON in power diode.
이기는 경영! 악착같이,될때까지,끝까지!
31/47

32. Switching waveforms
A power diode requires a finite time to switch from the blocking state (reverse bias) to the on state (forward bias).
Both the transition times and the shapes of the waveforms are affected by the intrinsic properties of the diode and by the circuit in which the diode is embedded.
The power diodes are very often used in circuits containing inductances that control the rate of change of current, or the diodes are used as freewheeling diodes where the turn-off of a solid-state device controls di/dt.
trr
tfr
이기는 경영! 악착같이,될때까지,끝까지!
32/47

33. Outline HV Floating MOS-Gate Driver ICs
Gate drive requirements of high side devices
Block diagram of a typical MGD (MOSFET Gate Drive)
Bootstrap operation
How to select the bootstrap components
The power dissipation in the MGD
이기는 경영! 악착같이,될때까지,끝까지!
33/47

34. 1. Gate Drive Requirements Of High-Side Devices
Gate voltage must be 10-15V higher than the drain voltage. Being a high side switch, such gate voltage would have to be higher than the rail voltage, which is frequently the highest voltage available in the system.
The gate voltage must be controllable from the logic, which is normally referenced to ground. Thus, the control signals have to be level-shifted to the source of the high side power device, which, in most applications, swings between the two rails.
The power absorbed by the gate drive circuitry should not significantly affect the overall efficiency.
이기는 경영! 악착같이,될때까지,끝까지!
34/47

35. 1-1. Gate Drive Method Of High-Side Devices
이기는 경영! 악착같이,될때까지,끝까지!
35/47

36. 2. A Typical Block Diagram
VDD/ VBS
LEVEL
TRANSLATOR
2.1. Input logic
Controlled by TTL/CMOS compatible inputs.
Schmitt trigger buffers with hysteresis equal to 10% of VDD to accept inputs with long rise time.
Application that require a minimum deadtime should use MGDs with independent drive and relay on a few passive components to build a deadtime.
The propagation delay between input command and gate drive output is approximately the same for both channels at turn-on (120ns) as well as turn-off (95ns) with a temperature dependence characterized .
The signals from the input logic are coupled to the individual channels. This allows the ground reference of the logic supply (VSS on pin 13) to swing by ±5V with respect to the power ground (COM).
이기는 경영! 악착같이,될때까지,끝까지!
36/47

37. 2.2. Low Side Channel 2.3. High Side Channel
The output stage is implemented either with two N-Channel MOSFETs or with an N-Channel and a P-Channel CMOS inverter stage.
Each MOSFET can sink or source-gate currents from 0.12 to 2A, depending on the MGD.
The source of the lower driver is independently brought out to pin 2 so that a direct connection can be made to the source of the power device for the return of the gate drive current.
2.3. High Side Channel
This channel has been built into an “isolation tub” capable of floating from 500 or 600V to -5V with respect to power ground (COM).
The gate charge for the high side MOSFET is provided by the bootstrap capacitor which is charged by the 15V supply through the bootstrap diode during the time when the device is off .
이기는 경영! 악착같이,될때까지,끝까지!
37/47

38. 3. How To Select The Bootstrap Components
Qg = Gate charge of high side FET
f = frequency of operation
Icbs(leak) = Bootstrap capacitor leakage current
Ilson = 20mA, Ilsoff =20mA, tw=200ns
Vf = Forward voltage drop across the bootstrap diode
VLS = Voltage drop across the low side FET or load
Qls = level shift charge required per cycle = 5nC (500V/600V IC’s) or 20nC (1200V IC’s)
The bootstrap diode must be able to block the full voltage seen in the specific circuit
→ This occurs when the top device is on and is about equal to the voltage across the power rail.
The high temperature reverse leakage characteristic of this diode can be an important parameter in those applications where the capacitor has to hold the charge for a prolonged period of time.
For the same reason it is important that this diode be ultrafast recovery to reduce the amount of charge that is fed back from the bootstrap capacitor into the supply.
이기는 경영! 악착같이,될때까지,끝까지!
38/47

39. QBOOT = CBOOT × VBOOT = QGATE × 20
If the capacitor is too large, time is wasted charging the capacitor, with the result being a limit on the maximum duty cycle and PWM frequency.
If the capacitor is too small, the voltage drop can be too large at the time the charge is transferred from the CBOOT to the MOSFET gate.
To keep the voltage drop small:
QBOOT >> QGATE
where a factor in the range of 10 to 20 is reasonable. Using 20 as the factor:
QBOOT = CBOOT × VBOOT = QGATE × 20
And
CBOOT = QGATE × 20 / VBOOT
The voltage drop on the BOOT pin, as the MOSFET is being turned on, can be approximated by:
Delta_V = QGATE / CBOOT
이기는 경영! 악착같이,될때까지,끝까지!
39/47

40. 4. The Power Dissipation In An MGD
a) Low voltage static losses are due to the quiescent currents from the three low voltage supplies VDD, VCC and VSS. In a typical 15V application these losses amount to approximately 3.5mW at 25°C, going to 5mW at TJ = 125 °C .
b) Low voltage dynamic losses on the VCC supply are due to two different components:
b1) Whenever a capacitor is charged or discharged through a resistor, half of energy that goes into the capacitance is dissipated in the resistor. Thus, the losses in the gate drive resistance, internal and external to the MGD.
b2)Dynamic losses associated with the switching of the internal CMOS circuitry.
c) High voltage static losses are mainly due to the leakage currents in the level shifting stage. They are dependent on the voltage applied on the VS pin and they are proportional to the duty cycle, since they only occur when the high side power device is on.
d) High voltage switching losses (PD(hv)sw) comprise two terms, one due to the level shifting circuit and one due to the charging and discharging of the capacitance of the high side p-well.
d1) Whenever the high side flip-flop is reset, a command to turn-off the high side device (i.e., to set the flip-flop) causes a current to flow through the level-shifting circuit.
d2) In a high-side/low-side power circuit the well capacitance Cb-sub is charged and discharged every time VS swings between VR and COM.
이기는 경영! 악착같이,될때까지,끝까지!
40/47

41. 5. How To Deal With Negative Transients On The VS PIN
Of the problems caused by parasitics, one of the main issues for control ICs is a tendency for the VS node to undershoot ground following switching events.
Improve local decoupling
a. Increase the bootstrap capacitor (Cb) value to above 0.47mF using at least one low-ESR capacitor. This will reduce overcharging from severe Vs undershoot.
b. Use a second low-ESR capacitor from Vcc to COM. As this capacitor supports both the low-side output buffer and bootstrap recharge, we recommend a value at least ten times higher than Cb.
c. If a resistor is needed in series with the bootstrap diode, verify that VB does not fall below COM, especially during start-up and extremes of frequency and duty cycle.
Look at the Vs spike during the reverse recovery
Reduce control IC exposure
a. Minimize parasitics in the gate drive circuit by using short, direct tracks.
b. Locate the control IC as close as possible to the power switches.
이기는 경영! 악착같이,될때까지,끝까지!
41/47

42. Power MOSFET Datasheet
Part
Number
Main
Features
Intended
application
Schematic
Package
Style 2
이기는 경영! 악착같이,될때까지,끝까지!
42/47

43. Electrical Characteristics
Breakdown Voltage
Off-state
Leakage current
Gate
Leakage
current
VGS
RDS,on
Cgd +Cgs gm
Cgd +Cds
Cgd 2
이기는 경영! 악착같이,될때까지,끝까지!
43/47

44. Reverse recovery time of the body diode
Switching Characteristics
switching
speed in
ns range
on-voltage
of the body
diode
Reverse recovery time of the body diode
이기는 경영! 악착같이,될때까지,끝까지!
44/47 2

45. Electrical Characteristic
slope = 1/RDS,on
slope = 1/RDS
saturation
characteristics not
important unless
for amplification
RDS,on decreases with
increases in VGS
RDS,on increases
with temperature
이기는 경영! 악착같이,될때까지,끝까지!
45/47 2

46. Body Diode Characteristic2
이기는 경영! 악착같이,될때까지,끝까지!
46/47

47. Operation must be inside this
Safe Operating Area (SOA)
maximum IDS
allowed by metal
connections
Current limited by RDS,on
thermal limit (max power dissipation)
Operation must be inside this
area
limited by breakdown voltage 2
이기는 경영! 악착같이,될때까지,끝까지!
47/47