Multispectral Imaging has recently made considerable improvements to the sensitivity, uniformity and
dynamic range of infrared FPAs based on capacitively read, bimorph microcantilever sensor technology. The
company is presently prototyping 160x120 imaging arrays with 50 μm pitch pixels and is actively pursuing the
development of next generation 25 μm pitch pixel arrays. Measured peak NETD values for recently fabricated 50μm pitch focal plane arrays are in the 40-50mK range, with individual pixels in the 10-15mK range. The modeled
and measured tradeoffs discussed in this paper lead to a possible 2-3 times further improvement in average NETD.
A number of factors influence the performance of these devices which includes the optimization of
sometimes competing design requirements. For example, the tuning and optimization of the infrared optical
resonant cavity structure while maximizing the change in sensor capacitance during IR irradiance. Similarly there
are tradeoffs between structural rigidity, which increases the structure resonant frequency improving noise
immunity, and thermal response times. These tradeoffs are discussed with reference to real world sensor
structures. Results from detailed thermo-electromechanical-optical modeling of the operation of the 25 μm pitch
pixels will be discussed in reference to the design and fabrication of 25 μm pitch test pixels. The most recent
infrared sensitivity and other performance measurements from the development of the company's first commercial
160 x 120 pixel imaging array product will also be presented.
This paper reports on the development of small pixel pitch infrared FPAs based on the capacitively read bimorph microcantilever sensor technology. The heat sensing bimorph microcantilever structures are fabricated directly onto the CMOS control and amplification electronics to produce a high performance, low cost imager that is compatible with standard silicon IC foundry processing and materials. Positional responsivities of greater than 0.3 μm/K have been modeled and measured for 50 μm pitch pixels, corresponding to a temperature coefficient of capacitance, &Dgr;C/C, (equivalent to TCR for microbolometers) above 30%/K. This responsivity, along with noise capacitances in the sub-attofarad range and nominal sensor capacitances of 15 fF, give modeled NEDT < 20 mK for these devices.
At smaller pixel pitches, the positional responsivity decreases rapidly with feature size resulting in increased system NEDTs. Modeling the performance of microcantilever based IR sensors with innovative sensor structures and pixel pitches down to 17 μm indicates NEDTs < 20 mK and thermal time constants in the 5 msec range, are feasible with this technology. Results from detailed thermo-electro-opto-mechanical modeling of the operation of the 25 μm pitch pixels are presented.
The design and operation of an advanced bimorph microcantilever based infrared imaging detector are presented. This technology has the potential to achieve very high sensitivities due to its inherent high responsivity and low noise sensor and detection electronics. The sensor array is composed of bimaterial, thermally sensitive microcantilever structures that are the moving elements of variable plate capacitors. The heat sensing microcantilever structures are integrated with CMOS control and amplification electronics to produce a low cost imager that is compatible with standard silicon IC foundry processing and materials. The bimorph sensor structure is fabricated using low thermal expansion, high thermal isolation silicon oxide and oxynitride materials, and a high thermal expansion aluminum alloy bimetal. The microcantilever paddle is designed to move away from the substrate at elevated imaging temperatures, leading to large modeled sensor dynamic ranges (~16 bits). A temperature coefficient of capacitance, ▵C/C, (equivalent to TCR for microbolometers) above 30% has been modeled and measured for these structures, leading to modeled NEDT < 20 mK and thermal time constants in the 5-10 msec range giving a figure-of-merit  NEDT.Tau = 100-200 mK.msec. The development efforts to date have focused on the fabrication of 160x120 pixel arrays with 50 micron pitch pixels. Results from detailed thermo-electro-opto-mechanical modeling of the operation of these sensors are compared with experimental measurements from various test and integrated sensor structures and arrays.
A novel low cost interferometric displacement sensor has been developed which tracks distance from the tip of a fiber optic probe. A unique interrogation technique is used which produces a 32-bit phase word, giving the system a dynamic range greater than 10<SUP>9</SUP>. Therefore, a displacement resolution of less than 0.01 nm can be achieved with a full range of 6 mm. The measurement range can be extended beyond 10 m by simply adjusting the digital fringe counter and sacrificing resolution yet maintaining the greater than 10<SUP>9</SUP> dynamic range. Demodulation rates of 40 kHz have been achieved which facilitates dynamic measurements. Results from an application to hard disk (HD) profilometry are presented.
During the last several years a number of different transmitter options have been developed for the distribution of video signals over fiber optic links. These options, for the AM-SCM modulation format, include intensity-modulated DFM lasers and externally modulated CW light sources. In this paper several design alternatives are reviewed in terms of intrinsic performance and suitability for linearization. Laboratory data are also presented for a 1550 nm transmitter comprising a linearized external modulator and fiber amplifier.