ROHM's smartphone wearable devices use MEMS technology such as barometric sensor geomagnetic sensors

[ROHM Semiconductor (Shanghai) Co., Ltd., October 21, Shanghai] In recent years, with the popularity of smartphones and wearable devices, it is also possible to perform position detection in real time like GPS while moving indoors, and can accurately point to it. There are more and more 3D indoor navigation application solutions for destinations including stereo information. For example, a navigation function that identifies a location on a few floors, etc., can be provided. In order to realize such 3D indoor navigation, a sensor with higher precision than before is required, and ROHM newly developed a method of detecting the height by using a MEMS (Micro Electro Mechanical Systems) air pressure sensor and detecting the position by a geomagnetic sensor (MI). For more precise navigation.

[piezoresistive air pressure sensor]

The air pressure sensor is divided into different types of detection, and the ROHM's air pressure sensor utilizes the piezoresistive effect. The piezoresistive air pressure sensor utilizes a piezoresistive effect of a Gauge resistor (pressure resistance) formed by diffusing and ion-implanting a formed vacuum chamber and a silicon substrate on a film sheet (pressure-receiving portion) by etching or the like. (figure 1)

ROHM for smartphones and wearable devices

Figure 1: Cross-sectional view of the air pressure sensor

The piezoresistive effect is different from the piezoelectric phenomenon caused by stress, which is a phenomenon in which the electrical conductivity, that is, the electrical resistivity, changes due to the stress applied to the electrical resistance. This phenomenon is caused by the crystal lattice being distorted by the applied stress, which causes a change in the number and mobility of carriers in the semiconductor. When the diaphragm is bent by pressure, each Gauge resistor generates a stress corresponding to the amount of bending of the diaphragm. The resistivity of the Gauge resistor (piezoresistive) changes in proportion to the stress, and the resulting change in resistance is used as a voltage change to detect the gas pressure. However, since the change in the resistance is extremely small, the Wheatstone bridge circuit using four resistors achieves high sensitivity.

This time, ROHM has developed a barometric pressure sensor "BM1383GLV" that can detect barometric pressure information and detect altitude and height difference for the ever-expanding areas of smartphones, wearable devices and activity trackers. The mass production began in the month. This product incorporates the sensor development technology accumulated by ROHM for many years, and is equipped with high-precision MEMS for detection and A/D converter with low power consumption and high precision. It achieves the highest level of relative accuracy in the industry ±20cm (relative air pressure accuracy ± 0.024hPa). (Fig. 2) In addition, the conventional air pressure sensor has a problem that the detection accuracy at low temperatures is difficult to improve, and ROHM uses an original correction algorithm to perform temperature correction inside the IC to realize high-precision air pressure detection at a low temperature. (Fig. 3) At the same time, it is no longer necessary to equip the external microcontroller with the temperature correction function, which greatly reduces the design burden and successfully realizes miniaturization of the sensing module and the arithmetic module. As a result, the air pressure sensor with built-in temperature correction function achieves the smallest package size (2.5mm & TImes; 2.5mm & TImes; 0.95mm).

Figure 2: Example of air pressure detection results


Figure 2: Example of air pressure detection result Figure 3: Example of temperature dependent air pressure detection result

With the increasing use of air pressure sensors, there is an increasing demand for more accurate air pressure detection and height detection functions. At the same time, with the development of miniaturization and high performance of smartphones and wearable devices, The miniaturization requirements of sensors are also growing. To meet these needs, ROHM expects to start mass production of "BM1385GLV" in April 2016. This product inherits the characteristics of the BM1383GLV that has been mass-produced, and optimizes the MEMS and control circuits for air pressure detection to reduce the area by 36% compared with ROHM's previous products. It is the world's smallest package (2.0mm & TImes; 2.0mm & TImes; 1.0mm) Air pressure sensor. (Figure 4) (as of July 14, 2015 ROHM survey data)

ROHM for smartphones and wearable devices

Figure 4: PKG size diagram

[Geomagnetic sensor using MI component]

Conventionally, a Hall element is often used for a geomagnetic sensor that detects an azimuth. However, such a geomagnetic sensor has a problem of low accuracy, and has always hindered the spread of indoor navigation. In addition, MR (Magneto-Resistive) components with precision advantages are also used, but there are power consumption problems of mobile devices. In response to these problems, ROHM began business cooperation with Aichi Steel Co., Ltd. in 2013, and jointly developed a geomagnetic sensor using MI components that is leading the prior art in terms of accuracy and power consumption. The MI element refers to a component that applies a pulse current to a special amorphous wire and detects a change in the Magneto-Impedance at this time by a pickup coil formed by the periphery of the amorphous wire. ROHM's BM14×× series (chip size 2.0×2.0×1.0 mm) is an IC chip in which such an MI element is integrally packaged by an X-axis, a Y-axis, a Z-axis, and a control ASIC.

This geomagnetic sensor (MI sensor) has the following two characteristics. The first feature is that the detection accuracy error can reach ±0.3 degrees anywhere in the world. (Figure 5)

Combined with an analog front-end circuit equipped with a high-sensitivity MI element and a high-precision A/D converter with high noise immunity, the effect of sigma noise was successfully reduced to 0.06μT, which is only 1/7 of that of an ordinary product. As a result, the industry's highest azimuth detection accuracy error of ±0.3 degrees or less is achieved, which helps to promote the innovation speed of IoT and sensor networks, and realizes a new sensor application led by indoor navigation. The second feature is very low power consumption for mobile devices. (Image 6)

ROHM for smartphones and wearable devices
Figure 5: Comparison of azimuth error measurements Figure 6: Power consumption comparison

In order to improve the accuracy, the ordinary geomagnetic sensor needs to increase the number of sensing (calculation) times to obtain an average value. However, the high-sensitivity MI sensor can achieve high precision even if the number of sensing times is reduced, so that the amount of power required for arithmetic processing can be greatly reduced. . This product achieves the industry's smallest power consumption of 0.15mA (at 100Hz), which is only 1/20 of the average product, which is very helpful for long-term use of smartphones and wearable devices. Future applications of MI sensors with these advantages include Augmented reality services. This is a service that displays the reality in front of a smartphone or tablet, locks and recognizes the position information and orientation information of the object from its screen, and retrieves the information of the object from the Internet and superimposes it on the screen. In addition, if used in conjunction with the map service, services such as identifying the building in front of the building and automatically accessing the web page of the building can be realized. These are only possible with MI sensors with very high azimuth detection accuracy.

In the future, ROHM will continue to promote the development of small high-precision sensor products that are indispensable for sensor networks, and contribute to the world by continuously meeting market demands.

[About ROHM (Roma)]

Founded in 1958, ROHM (Rom) has been the world's leading semiconductor manufacturer since its initial production of resistors, which has been in production for more than half a century. ROHM's "business purpose" is: We always put product quality first. No matter how difficult it is, we will continue to provide a large number of quality products for domestic and foreign users, and contribute to the progress and improvement of culture.

After more than half a century of development, ROHM's production, sales and R&D networks are spread all over the world. Products cover a wide range of fields, including ICs, discrete components, optical components, passive components, modules, semiconductor applications, and medical devices. In the world electronics industry, ROHM's many high-quality products have been approved and praised by the market, becoming the leading company in system IC and the latest semiconductor technology.

[About ROHM (Roma) business development in China]

As a sales outlet in the Chinese market, ROHM Semiconductor Hong Kong Co., Ltd. was first established in 1974. Subsequently, ROHM Semiconductor (Shanghai) Co., Ltd. was established in 1999, ROHM Semiconductor Trading (Dalian) Co., Ltd. was established in 2003, and ROHM Semiconductor (Shenzhen) Co., Ltd. was established in 2006. In order to respond quickly and accurately to the requirements of the expanding Chinese market, ROHM has built a one-stop system in China that integrates development, sales and manufacturing with ROHM headquarters. As a feature of ROHM, we are actively pursuing sales activities of “close to customers” and strive to provide thoughtful services to our customers. Since the second half of 2010, we have added five branch offices in Xi'an, Chengdu, Chongqing, Wuhan, Changchun and other inland areas, and added a new Hefei branch in 2014. Currently, there are 21 sales outlets across the country. Including Hong Kong, Shanghai, Dalian, Shenzhen and its four branches (subsidiaries: Beijing, Tianjin, Qingdao, Changchun, Nanjing, Hefei, Suzhou, Hangzhou, Ningbo, Xi'an, Wuhan, Dongguan, Guangzhou) , Xiamen, Zhuhai, Chengdu, Chongqing). And, the distribution network is gradually expanding.

As a technical base, we have design centers and QA centers in Shanghai and Shenzhen to provide technical and quality support. The design center is equipped with development and design support staff who are proficient in various markets, and can make technical proposals for customer needs in the form of integrated solutions from software to hardware. Moreover, when the product has a bad situation, the QA Center will respond to the appeal within 24 hours.

As a production base, in 1993, a production plant was established in Tianjin (ROHM Semiconductor (China) Co., Ltd.) and Dalian (ROHM Electronic Dalian Co., Ltd.). Production of diodes, LEDs, laser diodes, LED displays, and optical sensors in Tianjin, power modules, thermal printheads, contact image sensing heads, image link modules, LED lighting modules, light sensors, and LED displays in Dalian Production, as the main production base of ROHM, continuously supplies high quality products to China and abroad.

In addition, as part of the social contribution activities, ROHM is also committed to strengthening cooperation with many research institutions and enterprises at home and abroad, and actively promoting the joint research and development activities of industry, academia and research. In 2006, it signed a joint industry-university framework agreement with Tsinghua University, and actively launched an industry-university alliance on the development of cutting-edge technology for electronic components. In 2008, the Tsinghua ROHM Electronic Engineering Museum was donated in Tsinghua University and completed in April 2011. In 2012, Tsinghua University established the "Tsinghua-ROHM Joint Research Center" and engaged in joint research projects such as "micro-energy devices, silicon emitters, biosensors, and digital broadcasting (demodulators) in China." In addition to Tsinghua University, ROHM also cooperates with Xi'an Jiaotong University, University of Electronic Science and Technology, Zhejiang University and Tongji University to achieve fruitful results.

Based on the technical strength, high quality and reliability that have been accumulated over the years, ROHM will build a solid cooperative relationship with customers through a solid technical support and customer service system integrating development, production and sales. The company has made positive contributions to improving customer product strength, customer business development and China's energy conservation and environmental protection.

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