The goal of this project is to provide a research infrastructure of networked sensors for the College of Engineering at UC Berkeley. The infrastructure is intended to survive for a year on the energy from a pair of AA batteries per sensor node. It will support multiple applications simultaneously and allow public data retrieval from the Internet.
The goal of this project is to develop an ultra low power integrated circuit that will form the core of a self-contained, millimeter-scale sensing and communication platform for a massively distributed sensor network. The integrated circuit will contain sensor signal conditioning circuits, a temperature sensor, an A/D converter, microprocessor, SRAM, communications circuits, and power control circuits (Figure 1). The IC, together with the sensors, will operate from a power source integrated with the platform.
Smart Dust are millimeter-scale sensing and communication platforms [1,2] composing a distributed sensor network that can monitor environmental conditions in both military and commercial applications. These networks consist of hundreds to thousands of dust motes and a few interrogating transceivers. The motes are built from integrated circuit and micromachining processes for low-cost, low-power consumption , and small size. Communication between the motes and the receiver is accomplished via a wireless optical communication link at 1 kb/s or less.
We have demonstrated a 138 mm3 autonomous uni-directional sensing/communication mote that optically transmits a measure of the incident light level and a 63 mm3 autonomous bi-directional communication mote .
We have demonstrated a 16 mm3  autonomous solar-powered sensor node with bi-directional optical communication (Figures 2-4). The device digitizes integrated sensor signals and transmits and receives data optically. The system consists of three die: a 0.25 µm CMOS ASIC, a trench-isolation SOI solar cell array, and a micromachined four-quadrant corner-cube retroreflector (CCR, see Lixia Zhou’s research abstract), but a new MEMS process is being developed that will integrate the solar cells, CCR, and a capacitive accelerometer, yielding a 6.6 mm3 device.
A finite state machine (FSM) controls the system by multiplexing sensors, directing the ADC to take samples, and sending data to the CCR transmitter. The optical receiver operates at 375 kb/s and consumes 26 µW at 2.1 V (69 pJ/bit). The 8-bit serial ADC consumes 3.1 µW at 1 V and 100 ksamples/sec (31 pJ/sample, 4 pJ/bit). The ASIC also contains a 200 x 200 µm photosensor that provides a measure of the ambient light level.
We are just completing the testing of an ultra-low energy microprocessor that consumes less than 20 pJ/instruction (this is 1-2 orders of magnitude less than many "low power" microprocessors) and is tailored to distributed wireless sensor networks. It is 600 µm on a side. This will dramatically increase the intelligence of the mote and provide data storage and computational capability.
Figure 1: Smart Dust mote conceptual diagram
Figure 2: System diagram of the Golem Dust mote and annotated layout of the integrated circuit. Because light shields cover the active circuits, die photos are not very interesting.
Figure 3: 11.7 mm3 mock-up of Golem Dust system, showing a 0.25 µm CMOS ASIC, solar power array, accelerometer, and CCR, each on separate die. A new process is being developed to integrate everything but the ASIC into one die, which will decrease the circumscribed volume to 6.6 mm3.
Figure 4: Photograph of the mock-up in Figure 2.
Figure 5: Layout of a test chip containing the custom ultra-low energy microprocessor (large block in the upper left) and custom low power 1 k x 8 and 1 k x 17 SRAMs.
In this project, a CMOS imaging receiver will be designed to receive low-power, free-space optical transmissions between unmanned aircraft, or other small, low power platforms, at a distance of several kilometers.
The goal of this project is to guide the development of sensor network theory. In this nascent field, it is important to intelligently design experiments that explore the capabilities and discover the limitations of data collection from sensor networks. We seek to design quantifiable measures of algorithmic performance, apposite terminology, and paradigmatic perspectives to aid in the development of an information theory.
The scanning micromirror has attracted much attention due to its wide range of applications, such as free space communication, projection display, spatial light modulation, etc. Scanners which have a large range of deflection ability, low voltage actuation, and fast dynamic response are preferred. A large amount of work has been done on developing processes which have the capability of realizing 2Dof micromirrors.
Figure 1 shows the schematic principle of micromirror actuation. An off-axis lateral force is acting on the torsional suspension beam and induces the torsional movement of the micromirror. In the previous approach , multi-layer structures were realized through STS timing etch. Timing etch has a few disadvantages, such as wafer-across nonuniformity and process condition variation. The thickness of the low SCS and upper SCS layer is hard to control. This affects the process yield and makes the design difficult.
The new method involves the alignment bonding of patterned SOI/SOI wafers. Unlike the timing etch process, the thickness of the most critical layer, the upper SCS layer, is predetermined by the device layer of the SOI wafer. This approach has much better wafer-across uniformity and the process yield is much higher. Figure 2 shows the process flow. First two SOI wafers are patterned and etched individually. Then they are prebonded by Ksaligner and annealed at 1200 degrees for 24 hours. STS backside etch and handle wafer etch are performed afterwards. Finally, the bonded wafer is released in concentrated HF for a couple of minutes.
Figure 3 shows the picture of a fabricated 2Dof scanning mirror. The preliminary testing result shows that a 1Dof mirror is deflected 11 degrees optically under an actuation of 53 V, compared with the result of 6 degrees at 56 V from the timing etch process. Finer tuning of the design parameter and more tests are on the way.
Figure 1: Torsional movement of a micromirror induced by off-axis lateral actuation
Figure 2: Process flow of patterned SOI/SOI wafer bonding
Figure 3: Picture of a fabricated 2D scanning mirror (left corner: a SEM picture of the multi-layer structure)
The goal of this project is to develop steered narrow-beam optical communication devices capable of communicating wirelessly from a cubic-millimeter autonomous sensing platform.
The goal of the Cots-Bots project is to use commercial off-the-shelf (COTS) components to build and deploy inexpensive and modular robots, which can be used to investigate algorithms and cooperation in large (>50) robot networks. Distributed robot networks have applications ranging from mapping and exploration to constructing complex systems. Work in BSAC is targeted toward providing a standard robot platform with a variety of modular sensor and actuator boards to test algorithms to solve these problems. Many of the algorithms demonstrated on the cots-bots platform will find future use in the Microrobot project.
The goal of the cots-bots project is to use commercial off-the-shelf (COTS) components to build and deploy inexpensive and modular robots which can be used to investigate algorithms, and for cooperation and distributed sensing in large (> 50) robot networks. Current work is targeted towards providing a standard robot platform (both hardware and software) with a variety of modular sensor and actuator boards. The software used is based on the TinyOS operating system developed by Professor David Culler's group. Because the robots are intended to be simple in terms of computation, communication, and sensors, many of the algorithms demonstrated on the CotsBots platform will find future use in the MEMS Microrobot project.
To date, 50 robots have been built, a software platform has been developed, a simulator has been created, and work has begun on a low-cost inertial navigation system. Current algorithms being investigated include localization, robot diffusion, mapping, and pursuit-evasion games.
Figure 1: An example of a CotsBots robot--all hardware components are off-the-shelf and the software is open-source. The goal is to create an inexpensive and modular robot platform on which to test a variety of distributed robot algorithms.
The focus of this project is to create a class of articulated autonomous microrobots with a volume of less than 1 cm3.