Basic Knowledge of Discrete Semiconductor Devices

Transcription

1 Basic Knowledge of Discrete Semiconductor Devices Chapter II Diodes TVS Diodes(ESD Protection Diodes) Schottky Barrier Diodes July 2015 Semiconductor & Storage Products Company Toshiba Corporation

2 Types of Diodes Diodes are two-terminal semiconductor devices with a PN junction or an alternative junction. Table 2-1 shows an example of classification of diodes. They are classified into rectifier diodes, Zener diodes, etc. by structure and usage. Diodes are widely used. Table 2-1 Example of classification of diodes Diodes PN junction diodes Metal-semiconductor junction diodes Rectifier diodes (1SSxxx, CRGxx) Fast recovery diodes (FRD) (CMFxx, CMHxx ) TVS diodes (ESD protection diodes) (DF2Sxx, DF3Axx, DF5Axx ) Zener diodes (CRZxx, CMZxx) Variable-capacitance diodes (1SVxx, JDVxx ) High-frequency diodes (1SVxx, JDPxx) Schottky barrier diodes (SBD) (1SSxx, DSxx, CRSxx ) High-frequency detection diodes (1SSxx, JDxxx) Usage: Diodes are also classified into those for signal control and for power control. 2

3 Functions of Rectifier Diodes Rectifier diodes let current flow (forward) or do not let current flow (reverse) depending on the direction in which voltage is applied. They change AC voltage to DC voltage. Electrodes are called anode (A) and cathode (K), and when positive voltage is applied to the anode, current flows. Anode (A) Forward Cathode (K) Marking of cathode Anode (A) P Type N Type Cathode (K) Fig. 2-1(a) Symbol of diode and names of its electrodes General-purpose diodes use this region Forward Current Fig. 2-1(b) Example of appearance of diode + - Fig. 2-1(c) Polarity of diode Reverse Voltage Forward Voltage AC Voltage Reverse Current Fig. 2-1(d) Typical characteristic of diode Note: Symbol of cathode K is derived from German. Fig. 2-2 Typical function of diode 3

4 Forward Characteristic of Rectifier Diodes (I F -V F Characteristic) log Q Rating: I F(AV) I F (A) I FSM π I F(AV) (T j max) Forward characteristic of rectifier diode varies according to current level and temperature. At low-current region, V F is low at high temperature, and the opposite is true at highcurrent region. Diodes are generally used under the Q point, the cross point of the two conditions. ΔV F = 2 mv/ (1.98) V F (V) Controlled by carrier mobility in this region: The higher the temperature, the lower the V F At high temperature, carriers are easily movable and thus V F is lower than at low temperature. Controlled by carrier collision in this region: The higher the temperature, the higher the V F Many carriers must be moved to flow more current. At high temperature, carriers easily collide and thus V F is higher than at low temperature. 4

5 FRDs (Fast Recovery Diodes) The mechanism and function of fast recovery diodes (FRDs) are the same as those of rectifiers. Whereas rectifier diodes are used in sub-500 Hz applications, FRDs are used in several khz to 100 khz switching. Therefore, their switching characteristic of reverse recovery time (t rr ) is fast. FRDs are also referred to as S-FRDs, HEDs, etc. according to the t rr index. Whereas t rr of general-purpose rectifier diodes is from several μs to several tens of μs, t rr of FRDs is from several tens of ns to several hundreds of ns, about 1/100 the speed of a general-purpose rectifier. FRDs are used in switching power supplies, inverters, DC/DC converters, etc. Loss Current I F t rr =several μs to several tens of μs t rr =several tens of ns to several hundreds of ns V F FRD General-purpose rectifier t rr Voltage Fig. 2-3(b) Comparison of t rr between general-purpose rectifier and FRD Fig. 2-3(a) Example of diode switching waveform and loss Loss by t rr (reverse recovery loss) can be ignored at low frequency, but it increases as frequency increases, and cannot be ignored at frequency of over several khz. 5

6 Voltage Regulator Diodes (Zener Diodes) Voltage regulator diodes utilize the reverse characteristics of a PN junction. When raising reverse voltage of PN junction diodes, high current starts flowing at a certain voltage, and constant voltage can be obtained. (This phenomenon is called the breakdown phenomenon and the voltage is called the breakdown voltage). Voltage regulator diodes exploit this characteristic. The breakdown voltage is also called the Zener voltage, and this diode is also called a Zener diode. The voltage obtained is used for constant voltage power supply or standard voltage of electric circuits. (Note: Generally, the Zener phenomenon is observed when the voltage is six V or below. When the voltage exceeds six V, the avalanche phenomenon tends to be dominant, not the Zener phenomenon. The same behavior in MOSFET is called avalanche. Whereas the Zener voltage has a negative thermal characteristic, the avalanche voltage has a positive one. Anode (A) Cathode (K) Fig. 2-4(b) Symbol of Zener diode Z is added to the normal diode symbol. Zener diodes use this region V R Anode (A) P-type N-type + Current Fig. 2-4(a) Structure and connection of ESD protection diodes use this region. Reverse Voltage Zener diode Reverse Current Cathode (K) Forward Current Fig. 2-4(c) Electrical characteristic of Zener diode R Forward Voltage V F 6

7 TVS Diodes (ESD Protection Diodes) TVS diodes (ESD protection diodes) are a type of Zener diodes. They are mainly used as a countermeasure for ESD noise. They protect integrated circuits from static electricity (ESD) with high voltage coming from USB line etc. ESD protection diodes absorb abnormal voltage from interfaces, external terminals, etc., prevent unwanted operation of circuits and protect devices. They are suitable for absorbing and suppressing static electricity or short-pulse voltage. Connector Driver IC or Control IC absorb Fig. 2-5(a) Example of usage of ESD protection diodes Matrix display Matrix circuit ESD protection diodes protect devices such as ICs and prevent unwanted operation by absorbing static electricity (ESD). OFF ON Bidirectional OFF ON DF2S6.8FS DF2B6.8FS Block! When LED is OFF, wraparound current is created When LED is OFF, wraparound current is blocked Fig. 2-5(b) A bidirectional ESD protection diode is suitable for preventing wraparound current on a matrix circuit 7

8 Difference between ESD Protection Diodes and Zener Diodes (1) As shown in Fig. 2-6(a), an ESD protection diode absorbs very high voltage in a short time and prevents application of voltage over a certain level to other semiconductor devices. On the other hand, as shown in Fig.2-6(b), a Zener diode clamps input voltage to a constant voltage and supplies clamped voltage to other semiconductor devices. Thus, an ESD protection diode absorbs surge voltage to protect other semiconductor devices, whereas a Zener diode provides constant voltage to other semiconductor devices. ESD Protection diode Absorbing and controlling static electricity and short-time pulse Zener diode Constant voltage control Standard voltage Voltage level Short-time pulse of several 100 to several kv Absorbing, suppressing region Both diodes have the function of clamping certain voltage, but their usage is different. Voltage level Unstabilized voltage Constant voltage region Fig. 2-6(a) Usage of ESD protection diode Fig. 2-6(b) Usage of Zener diode 8

9 Difference between ESD Protection Diodes and Zener Diodes (2) Current Usual usage region ESD input Reverse Voltage [ESD protection diode: See Fig. 2-7(a).] ESD protection diodes are usually used under reverse blocking status (Virtually no current flows and only voltage is applied). When voltage exceeding a certain voltage (clamp voltage) is applied to an ESD protection diode, breakdown (clamp) occurs. Fig. 2-7(a) ESD protection diode usage region Current Usual usage region [Zener diode: See Fig 2-7(b).] Zener diodes are usually used under breakdown status with a certain current. It is assumed that breakdown (Zener) current flows. Reverse Voltage Fig. 2-7(b) Zener diode usage region 9

10 Variable-capacitance Diodes (Varicap Diodes) Variable-capacitance diodes use depletion layer s capacitance that is generated by applying reverse voltage to diode s PN junction. Depletion layer works as capacitance (capacitor), and its thickness varies proportionally to applied voltage. As applied reverse voltage increases, the distance between the capacitor s two electrodes appears to widen and diode s capacitance decreases. In the case of low applied voltage, its capacitance increases. To vary frequency characteristic by capacity variation, variablecapacitance diodes need to have a large capacitance ratio. They are used in tuning circuits. (All PN junctions and the like have this capacitance characteristic.) Variable-capacitance diode uses this Symbol of region diode Reverse Voltage Forward current Forward Voltage Symbol of capacitor Anode (A) P Type Smaller reverse voltage P Type Depletion layer Cathode (K) N Type Depletion layer narrows. Depletion layer N Type + + Capacitance increases. V R V F Fig. 2-8(a) Reverse Current Electrical characteristic of variable capacitance diode Fig. 2-8(b) Symbol of variable-capacitance diode Bigger reverse voltage Depletion layer widens. Capacitance decreases. Fig. 2-8(c) Relation between depletion layer and capacitance of variable-capacitance diode 10

11 Variable-capacitance Diodes (Varicap Diodes) Important characteristics of variable-capacitance diodes are neither forward voltage V F, nor switching characteristics as in the case of other diodes, but capacitance characteristics and variation of capacitance (voltage dependence). + C xv r s r s : serial equivalent resistance 11

12 Schottky Barrier Diodes (SBDs) A Schottky barrier diode (SBD) employs a junction between semiconductor and metal such as molybdenum instead of PN junction. N-type semiconductor and metal junction products have been commercialized. SBD is suitable for high-speed switching applications, because of small forward voltage and short reverse recovery time. For SBD, there is a tradeoff between forward voltage and reverse leakage current. Depending on the metal adopted, its reverse voltage ranges from 20 to 150 V, forward voltage (V F ) ranges from 0.4 to 0.7 V. These voltages are lower than for PN junction diodes. A new-structure SBD, which has entered production, keeps low forward voltage while suppressing leakage current. (Toshiba has achieved low V F and low leakage current by creating a trench structure in N-type semiconductor layer at a metal junction.) Cathode (K) Reverse voltage : V R Forward current: I F Symbol + Fig. 2-9(a) Symbol and structure of Schottky barrier diode More leakage current than for PN junction N Type Reverse current : I R Anode (A) Current Forward voltage: V F Fig. 2-9(b) Electrical characteristic of Schottky barrier diode 12 Metal R Lower forward voltage than PN junction

13 Reverse Recovery Characteristic of Schottky Barrier Diodes (SBDs) Metal C t : Junction capacitance C t Junction capacitance C t is maximum at V=0 V V Si (N Type) V C t L s L s : Stray inductance of circuit Fig. 2-10(a) Equivalent circuit when reverse voltage is applied to SBD 0 V Fig. 2-10(b) Characteristic of junction capacitance of SBD V I F t rr = π L C s t Characteristic of reverse current has attenuated oscillation Fig. 2-10(c) Typical reverse characteristic of SBD t SBD s reverse recovery time depends on its junction capacity and inductance of external connection. Because temperature has little effect on this junction capacitance, t rr characteristic of SBD is not changed by temperature. (t rr is the same from normal temperature to high temperature.) On the other hand, higher temperature makes t rr slow in the case of PN junction diode. The advantage of SBD s switching characteristic becomes evident at high temperature. SBD is suitable for high-frequency switching. 13

14 Difference Depending on Metal of Schottky Barrier Diodes (SBDs) In the case of SBD, metal works as anode of PN junction diode. Because the semiconductor is N-type layer, only electrons are carriers and, like MOSFET, SBD is a unipolar device. Difference of energy level of silicon and metal (energy gap) varies depending on the type of metal. ΦB is the symbol for this difference. Pt (platinum) has big ΦB. V (vanadium), Ti (titanium), etc. have small ΦB. Adopting big ΦB metals makes leakage current small, but makes forward voltage V F big. On the other hand, small ΦB metals realize the opposite characteristics. (OFF duration) Anode Metal (Mo, Ti, Pt etc.) (ON duration) I Anode SiO 2 N- Depletion layer N- N+ N++ Cathode I: Current does not flow N+ N++ Cathode Pt Mo V Ti ΦB Big Small V F I RRM Big Small Small Big Work function of metal ΦB: Barrier height (Schottky barrier) Work function of Si 14

15 Comparison of V F -I F Characteristics and Introduction of Application Fields of Various Diodes (SiC Di/Si Di) Types of diodes SiC SBD SiC, PN junction diode Application examples or expected application fields PFC (Power Factor Correction) in highefficiency power supply IGBT FWD (Free-Wheeling Diode) in AC drive DC transmission of HVDC AC drive of traction system I SiC SBD Si SBD Mo/V Battery of mobile equipment Pt/Ti Rarely used PN junction Di V Ti/Mo/Pt SBD from left SiC SBD Reverse voltage: 1200 V 150 to 175 PN junction Di Reverse voltage: 600 V 125 to 150 Pt Mo Ti Si SBD Reverse voltage : 30 V to 60 V 100 to 125 (Ti)V F =0.4 V (Mo)V F =0.55 V (Pt)V F =0.6 to 0.7 V 15

16 RESTRICTIONS ON PRODUCT USE Toshiba Corporation, and its subsidiaries and affiliates (collectively "TOSHIBA"), reserve the right to make changes to the information in this document, and related hardware, software and systems (collectively "Product") without notice. This document and any information herein may not be reproduced without prior written permission from TOSHIBA. Even with TOSHIBA's written permission, reproduction is permissible only if reproduction is without alteration/omission. Though TOSHIBA works continually to improve Product's quality and reliability, Product can malfunction or fail. Customers are responsible for complying with safety standards and for providing adequate designs and safeguards for their hardware, software and systems which minimize risk and avoid situations in which a malfunction or failure of Product could cause loss of human life, bodily injury or damage to property, including data loss or corruption. Before customers use the Product, create designs including the Product, or incorporate the Product into their own applications, customers must also refer to and comply with (a) the latest versions of all relevant TOSHIBA information, including without limitation, this document, the specifications, the data sheets and application notes for Product and the precautions and conditions set forth in the "TOSHIBA Semiconductor Reliability Handbook" and (b) the instructions for the application with which the Product will be used with or for. Customers are solely responsible for all aspects of their own product design or applications, including but not limited to (a) determining the appropriateness of the use of this Product in such design or applications; (b) evaluating and determining the applicability of any information contained in this document, or in charts, diagrams, programs, algorithms, sample application circuits, or any other referenced documents; and (c) validating all operating parameters for such designs and applications. TOSHIBA ASSUMES NO LIABILITY FOR CUSTOMERS' PRODUCT DESIGN OR APPLICATIONS. PRODUCT IS NEITHER INTENDED NOR WARRANTED FOR USE IN EQUIPMENTS OR SYSTEMS THAT REQUIRE EXTRAORDINARILY HIGH LEVELS OF QUALITY AND/OR RELIABILITY, AND/OR A MALFUNCTION OR FAILURE OF WHICH MAY CAUSE LOSS OF HUMAN LIFE, BODILY INJURY, SERIOUS PROPERTY DAMAGE AND/OR SERIOUS PUBLIC IMPACT ("UNINTENDED USE"). Except for specific applications as expressly stated in this document, Unintended Use includes, without limitation, equipment used in nuclear facilities, equipment used in the aerospace industry, medical equipment, equipment used for automobiles, trains, ships and other transportation, traffic signaling equipment, equipment used to control combustions or explosions, safety devices, elevators and escalators, devices related to electric power, and equipment used in finance-related fields. IF YOU USE PRODUCT FOR UNINTENDED USE, TOSHIBA ASSUMES NO LIABILITY FOR PRODUCT. For details, please contact your TOSHIBA sales representative. Do not disassemble, analyze, reverse-engineer, alter, modify, translate or copy Product, whether in whole or in part. Product shall not be used for or incorporated into any products or systems whose manufacture, use, or sale is prohibited under any applicable laws or regulations. The information contained herein is presented only as guidance for Product use. No responsibility is assumed by TOSHIBA for any infringement of patents or any other intellectual property rights of third parties that may result from the use of Product. No license to any intellectual property right is granted by this document, whether express or implied, by estoppel or otherwise. ABSENT A WRITTEN SIGNED AGREEMENT, EXCEPT AS PROVIDED IN THE RELEVANT TERMS AND CONDITIONS OF SALE FOR PRODUCT, AND TO THE MAXIMUM EXTENT ALLOWABLE BY LAW, TOSHIBA (1) ASSUMES NO LIABILITY WHATSOEVER, INCLUDING WITHOUT LIMITATION, INDIRECT, CONSEQUENTIAL, SPECIAL, OR INCIDENTAL DAMAGES OR LOSS, INCLUDING WITHOUT LIMITATION, LOSS OF PROFITS, LOSS OF OPPORTUNITIES, BUSINESS INTERRUPTION AND LOSS OF DATA, AND (2) DISCLAIMS ANY AND ALL EXPRESS OR IMPLIED WARRANTIES AND CONDITIONS RELATED TO SALE, USE OF PRODUCT, OR INFORMATION, INCLUDING WARRANTIES OR CONDITIONS OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, ACCURACY OF INFORMATION, OR NONINFRINGEMENT. Product may include products using GaAs (Gallium Arsenide). GaAs is harmful to humans if consumed or absorbed, whether in the form of dust or vapor. Handle with care and do not break, cut, crush, grind, dissolve chemically or otherwise expose GaAs in Product. Do not use or otherwise make available Product or related software or technology for any military purposes, including without limitation, for the design, development, use, stockpiling or manufacturing of nuclear, chemical, or biological weapons or missile technology products (mass destruction weapons). Product and related software and technology may be controlled under the applicable export laws and regulations including, without limitation, the Japanese Foreign Exchange and Foreign Trade Law and the U.S. Export Administration Regulations. Export and re-export of Product or related software or technology are strictly prohibited except in compliance with all applicable export laws and regulations. Please contact your TOSHIBA sales representative for details as to environmental matters such as the RoHS compatibility of Product. Please use Product in compliance with all applicable laws and regulations that regulate the inclusion or use of controlled substances, including without limitation, the EU RoHS Directive. TOSHIBA ASSUMES NO LIABILITY FOR DAMAGES OR LOSSES OCCURRING AS A RESULT OF NONCOMPLIANCE WITH APPLICABLE LAWS AND REGULATIONS. 16

17