From Device Supplier to Solutions Provider - The Need for Development Support Tools
Global semiconductor manufacturers are increasingly transforming from mere component suppliers to solutions providers that can quickly respond to customer requests. At the same time, to reduce customer design load, a greater emphasis is being placed on device simulation tools and platforms. ROHM, a leading semiconductor manufacturer based in Japan, is one company that is focusing on these initiatives. As an example, we will introduce simulation tools for SiC power devices (SiC) along with a sensor development platform.
At CEATEC Japan 2018, which was held in Tokyo from October 16 to 19, ROHM exhibited a mock-up of a vehicle that showcased as part of our automotive solutions. The demo allowed visitors to easily see where ROHM products can be used in the car. For example, one solution that garnered significant attention was an ultrasonic sensor for ADAS systems that can detect when a person or object approaches behind the vehicle and alert the driver by lighting up an LED. Another exhibit that attracted interest was a simulation tool and development platform that lowers the barrier to product introduction.
Accurate Simulation of SiC Power Device Characteristics
ROHM pioneered the development of SiC, which in recent years have been increasingly incorporated into a number of electric vehicle (EV) systems, including the onboard charger and main inverter for the motor. The advantages of adopting SiC are high-efficiency and greater miniaturization. SiC is characterized by low switching loss during power conversion. Power can be used more efficiently, making it possible to shorten the charging time and extend the cruising range. Also, compared to silicon IGBTs (Insulated Gate Bipolar Transistors), high speed switching is possible. This allows users to reduce the volume of coils and capacitors used in the power circuit. And since these passive components occupy a larger volume than the semiconductor part, the size of the inverter itself can be reduced significantly.
However, although SiC power devices are seeing widespread adoption, engineers are still faced with the difficult challenge of maximizing device characteristics. Helping to solve this problem is technology that enables the creation of a high accuracy device model for SiC MOSFETs, which ROHM introduced at CEATEC Japan. By using a model created utilizing this method, ROHM succeeded in obtaining results very close to the actual measurement for switching characteristics which are essential for circuit design.
Photo 1. New SiC MOSFET Model Creation Technology Introduced in Conjunction with the SiC Power Device
Of particular importance when creating a high accuracy device model is measurement of the current-voltage characteristics on which the device model creation is based. Current-voltage characteristics are typically observed using a curve tracer, but for the high voltage/high current region where SiC is able to exploit its large dielectric breakdown voltage and low on-resistance (i.e. 600V/100A), measurement cannot be performed due to the large self-heating of the device. In response, ROHM developed an original method for measuring the current-voltage characteristics with suppressing heat generation by employing switching characteristics. Using those current-voltage curves for model creation succeeded in obtaining simulated results for the turn ON waveform close to the measured results in the high voltage/high current region (graph at left in Fig.2). And to obtain a high accuracy turn OFF waveform (graph at right in Fig. 2), ROHM also developed a method for measuring the capacitance-voltage curve, which is another factor that determines the switching characteristics of SiC (in both active and inactive states of the transistor), then created a model using this curve.
In addition to devices, ROHM created models that include stray capacitances and parasitic inductances of the packages and boards that affect the switching characteristics of SiC when switched at high speeds, further improving the accuracy of simulated results.
Furthermore, using these models makes it possible to simulate noise generated during switching.
Figure 1. SiC MOSFET Switching Characteristics Simulation and Measured Waveforms
*For more details of this SiC MOSFET Modeling Technology, please check out our academic article.
Circuit simulations using high accuracy device models created using ROHM’s proprietary method can lead to a reduction in design man-hours for the set maker involved in the development, evaluation, and revision of the actual circuits. By providing a high accuracy device model, ROHM facilitates device introduction and contributes to the spread of SiC power devices.
Development Platform that Enables to Shorten the Development Period Dramatically
Sensors integrated in large quantities in applications such as cars and industrial equipment require development support tools. Ultrasonic sensors mentioned previously are one of examples. In order to use these sensors in an application it is first necessary to convert the signal from the sensor element (which possesses varying characteristics) into a digital signal for the MCU by using an AFE (Analog Front End) circuit. (‘AFE’ is also called ‘Signal Conditioner’.)
However, it is often extremely difficult to determine the AFE circuit specifications suitable for the particular sensor element. When designing the AFE one must take into consideration not only the type of sensor but the system specifications as well. So in addition to an instrumentation amp for capturing sensor signals it is also necessary to prepare an AD converter for each with respect to the required data conversion speed and resolution. This has created a demand for a sensor AFE development platform that can support a wide range of sensor elements.
Figure 2. Versatile Sensor System Supports a Variety of Applications and Sensor Elements
In addition to an analog circuit block comprised of instrumentation amps, Op-Amps, AD/DA converters, and comparators that support a wide range of sensor element characteristics and system specifications, ROHM’s FlexiblePlatform™ for sensor AFE (IC P/N: BD40002TL) introduced at CEATEC Japan 2018 includes a digital circuit block that consists of an MCU or FPGA capable of handling numerical calculations such as the averaging of measurement results and temperature compensation.
This platform provides users the flexibility to change both the digital and analog circuits of the IC utilizing ROHM’s GUI tool RapidMaker™ on a PC, making it possible to customize the AFE based on sensor and system specifications and enable evaluation on the actual device. Conventional AFE development is carried out separately from the sensor element, with device evaluation taking place at the final stage. Consequently, the development time is necessarily long, taking over a year in some cases - especially if revisions are needed. In contrast, with ROHM’s platform engineers can instantly confirm actual device operation soon, dramatically shortening the development period.
Photo 2. FlexiblePlatformTM for Sensor AFE Introduced at CEATEC Japan 2018
Development Support Tools that Reduce Set Design Load
As expectations for sophisticated, high-performance sets increase, set makers are no longer interested in semiconductor suppliers that simply introduce general products. This trend was seen at CEATEC Japan 2018, which recorded an attendance of 156,063, up 2.6% over the previous year, where a larger number of companies exhibited development tools and reference designs compared with the past. And going forward, the necessity for development support tools such as the ones introduced here is sure to increase, not only for the application side, but for the device side as well.