MONOLITHIC SURFACE-MICROMACHINED INERTIAL SENSORS:
      Design of Closed-Loop Integrated Accelerometers and Rate Gyroscopes

        Profs. Bernhard E. Boser, Roger T. Howe, and Albert P. Pisano*
    Depts. of Electrical Engineering and Computer Sciences and *Mechanical
                                  Engineering

                       Berkeley Sensor & Actuator Center
                     University of California at Berkeley

                                May 23-24, 1995
                             San Francisco Airport
                         Crown Sterling Suites Hotel,
                     150 Anza Blvd., Burlingame, CA 94010

Course Overview

Surface micromachining has enabled the integration of polysilicon
micromechanical structures with CMOS or Bipolar/MOS electronics. This
technology is already having a major impact in accelerometers for air-bag
deployment and has the potential for much higher performance accelerometers, as
well as vibratory rate gyroscopes. Successful design of these closed-loop
sensors requires a background in the microstructure and circuit technology, the
mechanical design of "laminar" suspensions and proof masses, and the system and
circuit approaches for sensing and controlling the position of the sense
element.

This two-day short course will supply the basic knowledge and the design
principles to understand the capabilities and limitations of surface
micromachined sensors for both accelerometers and for gyroscopes. During the
first day, participants will be introduced to the process, sense element, and
circuit fundamentals. The Analog Devices XL-50 monolithic accelerometer will be
discussed in detail as a motivating example. The second day will tackle the
design of high-performance inertial sensors and introduce several
domain-specific CAD tools. Fabrication constraints, packaging, sensor errors,
analog vs. digital closed-loop performance trade-offs, and system partitioning
are among the topics that will be addressed. A sigma-delta modular based
accelerometer will be used to focus the discussion. The course closes with an
open session for interaction with the lecturers.

Detailed up-to-date information including pictures of some of the course
material discussed can be accessed over the Internet at here

Other information/registration:
        email: [email protected]
        phone: (510) 642-4151 (general information)
               (510) 642-4111 (registration only)
        fax:   (510) 643-8683
        mail:  Continuing Education in Engineering
               University Extention
               University of California
               2223 Fulton Street
               Berkeley, CA 94720-7010
        fee:   $795 (including course materials)

Course Outline

Tuesday, May 23:

    I. Introduction

        Overview (1 hour)
            Technology (RTH)
            Sensing Elements (APP)
            Circuits and Systems (BEB)
        Surface Micromachining (RTH, 1 hour)
            Materials
            Processes
            Dimensions, Warpage, Stress, Stiction
        Mechanical Design of Sensing Elements (APP, 1 hour)
            Sensor Concepts (accelerometers and gyroscopes)
            Proof Masses
            Suspensions
            Resonant Frequencies
        Circuit Interfaces (BEB, 1 hour)
            Interfacing (Mechanics/Electronics)
            Capacitive position sensing and electrostatic actuation
            Open Loop vs. closed Loop Measurements
            Force feedback

    II. Design Example: 50g "Air Bag" Accelerometer (ADXL50)

        System Overview (BEB, 30 min.)
            sensor model
            feedback and stabilization
            low-noise position sense electronics
            self test
        Fabrication and Layout (RTH, 30 min.)
            3-D structure simulation (SIMPL)
            interdigitated sense capacitance and fringing fields
            simulation (FASTCAP)
        Mechanical Structure (APP, 30 min.)
            suspension and proof mass dimensioning
            resonant frequency calculations
            finite element simulation (ABAQUS)
        System Analysis (BEB, 30 min.)
            sensitivity and noise calculation
            system simulation (MATLAB \& MIDAS)
            performance summary
            discussion of limitations

Wednesday, May 24:

    III. High-Performance Integrated Sensors

        Technology (RTH, 1.5 hours)
            double structural polysilicon: the MICS process
            trimming by fuses, electrical springs
            microshell processes
            future prospects
        Mechanical Design and Optimization (APP, 1.5 hours)
            rate gyroscope design issues
            suspension options and constraints
            design tools
        Circuit/System (BEB, 2 hours)
            Feedback linearization
            Sigma-delta loops: quantization noise, stability
            Distortion
            Performance limits: Brownian, electronic, and quantization noise
            Design example

    IV. Course Wrap-Up (All, 1 hour)

        Perspectives (RTH/APP/BEB, 30 min.)
            Discussion (30 min.)

Instructor Biographies

Bernhard E. Boser received his Ph.D. in Electrical Engineering from Stanford
University in 1988. After 3 years at AT&T Bell Laboratories, he joined the
faculty of the Dept. of Electrical Engineering and Computer Sciences at the
University of California at Berkeley, where he is an Assistant Professor. His
research in analog IC design includes several projects in sensor interface and
control circuitry.

Roger T. Howe is a Professor in the Dept. of Electrical Engineering and
Computer Sciences at the University of California at Berkeley and Co-Director
of the Berkeley Sensor & Actuator Center. His research is on micromachining
technology for integrated sensors and actuators.

Albert P. Pisano is a Professor in the Dept. of Mechanical Engineering at the
University of California at Berkeley and Co-Director of the Berkeley Sensor &
Actuator Center. His research interests include design, optimization, and
fabrication of MEMS.