Data Storage Systems Center

A navigation system for CMOS MEMS probes is currently being developed utilizing LabView and other lab instrumentation to reconfigure phase change (PC) vias on integrated circuits. By utilizing conductive and non-conductive patterns on substrates, navigation on these structures is possible. The algorithm functions by moving a probe up and down incrementally towards a surface. When the probe comes into contact with a conductive surface, a small resistance is measured. A probe can follow conductive landmarks to a PC via location and deliver a current pulse to turn the PC via on or off.

CMOS-MEMS electrothermal probes with platinum metalized tips have been designed and characterized. These probes are being designed to access on-chip pads that route electrical current for on-chip on/off programming of phase change vias. The target is to use the probe via technology for reconfigurable RF circuits such as inductors. The MEMS probes offer a way to supply the reconfiguration current, while contributing no parasitic capacitance when disconnected.

Recently, a new “push-up” probe design with an embedded piezoresistive sensor has been successfully produced. The probes do not touch the chip pads when powered off. The new design allows more probe contact force to be applied as the drive power is increased. A 28.0 µm vertical upward actuation on unconstrained probes has been achieved with a 10 V, 20.0 mW drive to the embedded polysilicon heater resistors. The thermal cut-off frequency is 182 Hz, the mechanical resonant frequency is 20220 Hz, and the quality factor is 45. The thermal cross-talk at adjacent probes is about 2%. Thermal buckling is not observed. The probes are placed at the chip edges to convenience the alignment and registration in reconfiguration.

Piezoresistive sensors are developed to sense the force and thus to stabilize the contact resistance. A sensitivity of -71.45 ppm/μN is achieved. We are also designing capacitive sensors to achieve nanometer-scale position resolution. Tip platform platinum sputtering is developed to coat the probe tips with platinum to decrease the contact resistance. The contact resistance on the platinum tip is about 0.65 Ω. A 10 mA DC current is successfully passed through the contact. A less than 1% degradation is observed at thousands of I-V scan cycles. A future goal may be to complete a force servo to provide feedback to stabilize the contact force, and thus the contact resistance.

Atomic Force Microscopy(AFM) probes, both passive ones and active MEMS ones, are designed and fabricated, which are expected to be used in Tip Based nanofabrication.

Passive probes with silicon cantilevers and platinum tips are fabricated from MEMS SOI wafers. Tips are formed with a ‘Spindt’ tip process[1]. Cantilevers are defined with a front-side deep reactive-ion etch (DRIE) followed by backside through-wafer etch.

Active MEMS probes are made using post-CMOS MEMS processing techniques. The vertical (z) movement control of AFM tips is realized by electrothermal actuation, using metal/oxide bimorph as actuator beam structures. Capacitive height sensing is added in the active probe design to detect the tip-to-substrate spacing and, based on this feedback signal, the height of probe tips is controlled.

A navigation system for CMOS MEMS probes is currently being developed utilizing LabView and other lab instrumentation to reconfigure phase change (PC) vias on integrated circuits. By utilizing conductive and non-conductive patterns on substrates, navigation on these structures is possible. The algorithm functions by moving a probe up and down incrementally towards a surface. When the probe comes into contact with a conductive surface, a small resistance is measured. A probe can follow conductive landmarks to a PC via location and deliver a current pulse to turn the PC via on or off.

We present the realization of a novel three-terminal electronic switch using phase change (PC) chalcogenide material. This device subdivides a single phase change switch into a parallel array of three-terminal sub-vias which are addressed with atomic force microscopy (AFM) cantilever probes. This subdivision reduces the required switching current to acceptable levels as well as increasing the cooling speed of each sub-via (as compared to a single large via) by enhancing heat sinking effects. Vias of Ge50Sb50 are demonstrated in this switch topology, and are switched between high and low resistance states. Vias show an off/on resistance ratio of approximately 100x, which can be applied in RF switching applications. The resistivity in a re-amorphized state is comparable with that as-deposited state, which is different from behavior reported for other phase change materials, like Ge2Sb2Te5, where significant loss of dynamic range is observed after switch cycling.

A navigation system for CMOS-MEMS is currently being developed utilizing LabView and other lab instrumentation to reconfigure phase change (PC) vias on circuits. By utilizing conductive and non-conductive patterns on substrates, navigation on these structures is possible. When a probe determines it has found a PC via, it can then deliver a current pulse to turn the PC via on or off. This will allow different types of structures, such as inductors, to be reconfigured on a chip. The navigation system will also allow unknown structures to be examined and mapped out through resistive measurements. Work is currently ongoing to create and refine the navigation system so different test programs can be used to characterize CMOS-MEMS probes for use in reconfigurable circuits.

CMOS-MEMS electrothermal probes with nickel metalized tips have been designed and characterized. These probes are being designed to access on-chip pads that route electrical current for on-chip on/off programming of phase change vias. The target is to use the probe via technology for reconfigurable RF circuits such as inductors. The MEMS probes offer a way to supply the reconfiguration current, while contributing no parasitic capacitance when disconnected. Recently, a new “push-up” probe design has been successfully produced. The probes do not touch the chip pads when powered off. The new design allows more probe contact force to be applied as the drive power is increased. A 28.0 µm vertical upward actuation on unconstrained probes has been achieved with a 10 V, 20.0 mW drive to the embedded polysilicon heater resistors. The thermal cut-off frequency is 182 Hz, the mechanical resonant frequency is 20220 Hz, and the quality factor is 45. The thermal cross-talk at adjacent probes is about 2%. Thermal buckling is not observed. The probes are placed at the chip edges to convenience the alignment and registration in reconfiguration. Piezoresistive sensors are developed to sense the force and thus to stabilize the contact resistance. A sensitivity of -71.45 ppm/μN is achieved. We are also designing capacitive sensors to achieve nm-scale position resolution. Yield and reliability of Ni-plating is not so good. A more reliable metallization process, platinum sputtering, is being developed. A future goal may be to complete a force servo to provide feedback to stabilize the contact force, and thus the contact resistance.