SiC-SBD and Si-FRED: Who can break the performance ceiling of power semiconductor devices?

[Guide]Power semiconductor devices, also known as power Electronic devices, are high-power electronic devices used for power conversion and control circuits of power equipment. Because their performance is directly related to the amount of energy consumption, energy saving is now Under the general trend of emission reduction, much attention has been paid and it has become a focus of attention in the electronic circle.

Now that it has become the focus, everyone’s requirements for it will become higher and higher. If you want to draw a picture of “the ideal power semiconductor device in your mind”, I believe many people will make the following description:

1. High withstand voltage: Since it is dealing with larger power, the withstand voltage capability will be a hard indicator. For this reason, the manufacture of power devices often uses semiconductor processes different from general logic devices.

2. High frequency: A higher switching frequency can not only improve the performance of the power device itself, but also bring an obvious advantage, which is to allow the use of smaller peripheral components, thereby reducing the overall size of the system.

3. High reliability: Due to higher power density, power devices need to be resistant to high temperatures, have higher thermal stability, and have the ability to resist transients such as overcurrent and overvoltage.

4. Low power consumption: There are many factors that affect the power consumption of power devices. Taking a power diode as an example, its power consumption mainly includes the switching loss related to the reverse recovery process and the forward conduction loss related to the forward voltage drop VF , And the reverse loss caused by the reverse leakage current.

In reality, the developers of power devices follow this ideal appearance of “three highs and one low” to create products. But the trouble is that in the devices we know based on silicon (Si) materials, the above-mentioned advantages are difficult to achieve on a single device, and they are often contradictory to each other, so people have to Make a trade-off between.

The bottleneck of Si power devices

For users of power devices, it is also difficult to find a “perfect” device that can meet all their expectations of power devices, so they often get into entanglements when selecting materials.

Still taking diodes as an example, if you want to choose a “faster” device-that is, support higher switching frequencies-everyone will first think of Schottky barrier diodes (SBD), because SBD does not use PN junctions. It is a hot carrier diode made by the principle of the metal-semiconductor junction formed by the contact between metal and semiconductor. Therefore, there is no charge storage effect like a PN junction diode during reverse recovery, and a reverse recovery time is required. trr eliminates these charges, so its switching speed is very fast, and the switching loss is also small. But SBD has a shortcoming, that is, the reverse withstand voltage is not high, and it can only reach about 200V after process improvement. This can be said to be a “failure” in the application of power semiconductors.

If you want to increase the reverse withstand voltage, you must use a power diode with a PN junction structure, but due to the charge storage effect during reverse recovery, the speed is not fast. In order to solve this problem, fast recovery and ultra-fast recovery diodes (FRD) have been developed by doping precious metals in the diodes. As the name suggests, this device has found an optimum between high frequency and high withstand voltage. The balance point is to minimize the reverse recovery time trr (which can reach tens of nanoseconds) while ensuring sufficient reverse withstand voltage characteristics (usually above 1000V), resulting in higher conduction voltage drop, which is not worth the loss.

However, as long as it is a PN junction Si device, it will face the following challenges in terms of power consumption:

● When the forward direction is switched to the reverse direction, a large transient reverse recovery current will be generated during the “death” of the minority carriers accumulated in the drift layer, resulting in a large switching loss.

● The greater the forward current or the higher the temperature, the longer the recovery time, the greater the recovery current, and the greater the loss.

● As an SBD, if you want to reduce the forward turn-on voltage and reduce the forward conduction loss, the Schottky barrier must be lowered. However, the reduction of the Schottky barrier will increase the leakage current during reverse bias. It is a dilemma.

Therefore, from the above analysis, it can be seen that no matter which power diode is selected, it is not a “one-size-fits-all strategy.” The reason is that the Si material used to manufacture traditional power devices has reached its physical limit. It is difficult to improve even a small step in performance, and sometimes it will have a negative impact on other performance. Therefore, if you want to break the “ceiling” of power device performance improvement, it is not enough to just go around on the original semiconductor materials, and you must find a breakthrough in new materials.

Opportunities brought by SiC materials

So the third-generation wide-bandgap semiconductor materials have entered people’s field of vision. In fact, the research history of these materials is not short, but in recent years, the market and users’ desire to break through the performance bottleneck of power devices has promoted the acceleration of the development and commercialization of related materials. Among them, silicon carbide (SiC) is an important force.

In addition to excellent performance, SiC also has excellent thermal, mechanical and chemical stability, which provides a solid cornerstone for building a new generation of power devices.

Nowadays, the competition to develop innovative power devices using the excellent characteristics of SiC has begun. In this regard, Vishay has developed a new silicon carbide Schottky based on its deep technical accumulation in the field of power semiconductors and an in-depth understanding of SiC materials. Diode (SiC-SBD) products, these power diodes have a breakdown voltage of up to 650V, including 4A~20A single-tube devices and 16A~40A common-cathode dual-tube devices, which can work at a high temperature of +175˚C and have high waves Compared with traditional Si power diodes in terms of low power consumption, the surge protection capability is even better.

SiC-SBD and Si-FRED: Who can break the performance ceiling of power semiconductor devices?

Figure 1: Vishay’s new SiC-SBD product

After reading the performance parameters of Vishay SiC-SBD (see Table 1), you will definitely come to the conclusion-this is the power device that meets the “three high and one low” standard.

SiC-SBD and Si-FRED: Who can break the performance ceiling of power semiconductor devices?

Table 1: Main features of Vishay SiC-SBD products

How is Vishay SiC-SBD made?

How to make such excellent performance, let’s read it carefully below.

First of all, because SiC has 10 times the dielectric breakdown electric field of Si material, this means that even if the structure of SBD is used instead of the more withstand voltage PN junction, the reverse withstand voltage of SiC-SBD can be over 600V, even It can do thousands of volts. Vishay’s SiC-SBD has a rated reverse withstand voltage of 650V.

Secondly, SiC-SBD also inherits the high-frequency and high-speed characteristics of Schottky diodes. In principle, there will be no accumulation of minority carriers during the forward and reverse voltage conversion, and there will be no pressure when applied to high-frequency applications.

Furthermore, it is the most praised power consumption advantage of SiC devices.

● First, since SiC-SBD does not have the charge storage effect of the PN junction during reverse recovery, and only generates a small current that discharges the junction capacitance, compared with FRD, the switching loss is greatly reduced.

● Second, the impedance of general high withstand voltage power devices mainly depends on the impedance of the drift layer forming a high dielectric breakdown field strength. Compared with Si devices, SiC can have a higher impurity concentration and a thinner drift layer. To achieve sufficient withstand voltage characteristics, so the unit area on-resistance is very low, resulting in lower forward conduction losses.

● Third, in terms of reverse leakage current, Vishay’s SiC-SBD also does a good job, which can effectively control the reverse loss.

In addition, Vishay’s SiC-SBD has a feature that is particularly worth mentioning, that is, it uses a unique MPS (Merged PN Schottky) structure to bring higher surge protection capabilities to the device. Simply put, the MPS structure is to add a PN junction at the positive electrode of the SBD. When the device passes high current, this PN junction increases the conductivity of the drift region by injecting minority carriers, thereby controlling the forward voltage VF at a low level. . The effect of this is obvious. It can be seen from Figure 3 that as the forward current IF increases, the forward voltage VF of a “pure” SBD will increase exponentially; while the SBD using the MPS architecture does not matter whether the IF is high or low, VF will remain at a stable level, showing excellent surge protection capabilities.

SiC-SBD and Si-FRED: Who can break the performance ceiling of power semiconductor devices?

Figure 2: The difference between pure SBD structure (left) and SBD based on MPS process (right)

SiC-SBD and Si-FRED: Who can break the performance ceiling of power semiconductor devices?

Figure 3: Comparison of surge protection capabilities between SBD based on MPS process and pure SBD

Facing diverse needs

Through the above, everyone must have been impressed by the performance advantages of SiC-SBD, but when developers make realistic technical decisions, one of the “deficiencies” of SiC devices may still make people hesitate, that is-its The cost is relatively high.

After all, SiC is still a relatively new field, and the maturity of its technology and supporting industry chain today cannot be compared with Si devices. This also makes it difficult for SiC devices to cover the requirements of more comprehensive power electronic applications in the short term, especially those applications with higher cost-effectiveness than requirements.

It is for this reason that although silicon-based power devices have become closer to their theoretical performance “ceilings”, efforts to tap their performance potential in depth have not stopped, and this is also a test of the strength of manufacturers. Therefore, while accelerating the pace of innovation in its SiC power devices, Vishay is also constantly consolidating its advantages in silicon-based power devices. The fifth-generation FRED Pt® ultra-fast recovery diode is one of its masterpieces.

SiC-SBD and Si-FRED: Who can break the performance ceiling of power semiconductor devices?

Figure 4: Vishay 600V fifth-generation FRED Pt® ultra-fast recovery diode

For example, the 600V fifth-generation FRED Pt® ultra-fast recovery diode launched by Vishay supports currents from 15A to 75A. In some characteristics, it has the strength to be comparable to SiC-SBD.

1. Switching frequency: Compared with similar products, the performance of this series of products is very eye-catching. For example, the reverse recovery charge of the 15A VS-E5TX1506-M3 is only 578nC, and the reverse recovery time only needs 19nS.

2. Power consumption performance: The fifth-generation FRED Pt® has made systematic improvements in switching loss, forward loss and reverse loss characteristics. Therefore, in the 50kHz frequency application range, in addition to SiC devices, there can be one more cost-effective choose.

3. Working temperature: This series of products can support the same maximum working temperature of 175℃ as SiC-SBD.

4. Product portfolio: 600V fifth-generation FRED Pt® series products include X-type devices that focus on lower Qrr and shorter trr, as well as H-type devices that perform better in forward conduction voltage drop. Developers can Make flexible choices according to the requirements of the target application. Moreover, the current series can also provide automotive-grade products that meet the AEC-Q101 standard, which is even more good news for automotive electronics developers.

SiC-SBD and Si-FRED: Who can break the performance ceiling of power semiconductor devices?

Table 2: Vishay 600V 5th generation FRED Pt® ultra-fast recovery diode series product characteristics

By advancing side by side on the two technical routes of silicon-based FRD and SiC-SBD, Vishay can provide developers with more choices in response to diversified needs, whether they are pursuing higher performance or requiring excellent cost-effectiveness, Vishay According to the actual requirements of customers, we can provide excellent one-stop solutions.

The Links:   2MBI200L-060 TP-3142S2