Into High Gear

Denso, a $40-billion supplier of advanced automotive technology, systems and components for all of the world’s major automakers, has been using SOI since 1994.

In a recent paper entitled, “Automotive SOI-BCD Technology Using Bonded Wafers”1, Denso researchers had a chance to highlight the company’s long and successful experience with SOI.

The company’s semiconductor products include hybrid and custom integrated circuits installed on electronic control units (ECUs), and various sensors (for acceleration, pressure, cam/crank position and so forth).

Denso believes that the SOI structure is the most suitable choice for automotive semiconductor devices. Here’s why.

Automotive semiconductor devices have extremely demanding requirements. They are used under extreme condition of heat and humidity. They have to be extremely reliable and last far longer than ordinary consumer chips. And, they demand extremely high immunity to electrical noise.

SOI wafers are an excellent solution for high temperature operation and noise immunity. The integrated elements in an SOI design can be electrically separated by dielectric isolation, making them suitable for automotive semiconductors.

Denso was a world leader in recognizing these advantages, putting the first SOI-BCD (BiCDMOS) process to practical use for power ICs in 1994.

Today, the range of applications using SOI wafers has been greatly increased, and includes MEMS and MPUs.

Figure 1. Cross-section of an automotive SOI-BCD. (Courtesy: Denso)

Air-bags ECUs

In 2001, Denso researchers published a prescient paper in the Japan Journal of Applied Physics2 entitled, “A Single Chip Automotive Control LSI Using SOI Bipolar Complimentary MOS Double-Diffused MOS” (Kazunori Kawamoto, et al).

Using the example of an airbag controller, the paper explained how BiCDMOS and thick SOI enabled a single chip solution for automotive sub-control systems. It concluded that this single-chip solution could reduce the number of electronic parts by half, while improving the reliability of automotive electronic control units (ECUs).

Today, these SOI-based ECUs are found across a broad range of Denso’s ECUs.

Smart power and more

Figure 2. Denso’s used its advanced SOI-based MEMS technology to create the world's smallest automotive semiconductor acceleration sensors for safety systems such as airbag systems, vehicle stability control systems and anti-lock braking systems. (Courtesy: Denso)

Denso first began using SOI for smart power ICs in 1996 for automotive applications. In recent years, the company published a number of papers3,4 on manufacturing advances. The smaller design rules enabled new levels of integration.

For example, CMOS digital devices could be integrated on the same chip with DMOS (Double diffused MOS) transistors for power, high breakdown voltage bipolar transistors for analog, and thin-film resistors for high-precision resistors.

The non-parasitic elements and high temperature operation enabled an even wider range of ECU applications, as well as things like smart actuators for ISCV (Idle Speed Control Valves). Such automotive ICs play an ever more critical role in maximizing fuel efficiency, reliability, safety and respect for the environment.

SOI MEMS

At the 2007 Tokyo Motor Show, Denso presented new SOI-based MEMS technology that allows a deeper and narrower trench than ever before. The company is applying this technology in the world’s smallest automotive semiconductor acceleration sensors for safety systems such as airbag systems, vehicle stability control systems and anti-lock braking systems.

The acceleration sensor has a sensor element composed of fixed and movable electrodes that detect acceleration from a change in capacitance, and a control circuit that converts the change in capacitance to an electric signal.

The MEMS technology for sensor elements enables the world’s thickest fixed and movable electrodes to be formed on an SOI substrate using only a dry etching process (as opposed to both wet and dry). This technology simplifies manufacturing processes and improves production yield, resulting in a lower cost acceleration sensor.

The next step

As Denso is a supplier to every major automaker in the world, these SOI-based solutions are found in many of the latest car models. Denso is now taking the next step: accelerating integration of SOI-based automotive power ICs and increasing their use in a broadening range of applications. These new SOI-based solutions will help give automotive designers the range of cost-effective options they need to balance performance, fuel efficiency, safety and reliability.

Denso and Toyota developed this SOI-based power supply management ECU. It calculates the battery charge rate and internal resistance using battery voltage and current. When the battery charge rate is low, the ECU increases the alternator’s adjustment voltage for generating electricity or raises the engine revolutions during idling to stimulate battery charging. (Courtesy: Denso, Toyota)

References:
1) Himi et al, IIT 2008 (invited).
2) Kawamoto et al, Japan Journal of Applied Physics 40 (2001) pp. 2891-2896.
3) Iida et al, Denso Tech Rev, Vol.8, No.1 (2003), pp.87-92.
4) Kuzuhara et al, SAE Transactions, vol. 114, no 7 (2005), p. 926.

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