Microspectrometers based on the monolithic integration of a microelectromechanical system (MEMS) Fabry–Pérot filter and a Hg x Cd1–x Te-based infrared detector are discussed and measured results presented. The microspectrometers are designed to operate in the 1.5 μm to 2.6 μm wavelength range. Design equations are presented which account for the mechanical and optical characteristics of the device. Measurements indicate linewidths as narrow as 55 nm, switching times of 40 μs, and a tuning range of 380 nm, which is limited by snap-down. Optical characterization of the distributed Bragg mirrors and the Fabry–Pérot filter are presented, and these are shown to be in good agreement with simple first-order analytical models. Bowing of the movable Fabry–Pérot mirror due to stress gradients is identified as the dominant source of linewidth broadening.

Hyperspectral imaging in the infrared bands is traditionally performed using a broad spectral response focal plane array, integrated in a grating or a Fourier transform spectrometer. This paper describes an approach for miniaturizing a hyperspectral detection system on a chip by integrating a Micro-Electro-Mechanical-System (MEMS) based tunable Fabry Perot (FP) filter directly on a photodetector. A readout integrated circuit (ROIC) serves to both integrate the detector signal as well as to electrically tune the filter across the wavelength band. We report the first such demonstration of a tunable MEMS filter monolithically integrated on a HgCdTe detector. The filter structures, designed for operation in the 1.6-2.5 μm wavelength band, were fabricated directly on HgCdTe detectors, both in photoconducting and high density vertically integrated photodiode (HDVIP) detectors. The HDVIP detectors have an architecture that permits operation in the standard photodiode mode at low bias voltages (≤0.5V) or in the electron avalanche photodiode (EAPD) mode with gain at bias voltages of ~20V. In the APD mode gain values of 100 may be achieved at 20 V at 200 K. The FP filter consists of distributed Bragg mirrors formed of Ge-SiO-Ge, a sacrificial spacer layer within the cavity and a silicon nitride spacer membrane for support. Mirror stacks fabricated on silicon, identical to the structures that will form the optical cavity, have been characterized to determine the optimum filter characteristics. The measured full width at half maximum (FWHM) was 34 nm at the center wavelength of 1780 nm with an extinction ratio of 36.6. Fully integrated filters on HgCdTe photoconductors with a center wavelength of approximately 1950 nm give a FWHM of approximately 100 nm, and a peak responsivity of approximately 8×104 V/W. Initial results for the filters on HDVIP detectors exhibit FWHM of 140 nm.

Hyperspectral imaging in the infrared bands is traditionally performed using a broad spectral response focal plane array, integrated in a grating or a Fourier transform spectrometer. This paper describes an approach for miniaturizing a hyperspectral detection system on a chip by integrating a Micro-Electro-Mechanical-System (MEMS) based tunable Fabry Perot (FP) filter directly on a photodetector. A readout integrated circuit (ROIC) serves to both integrate the detector signal as well as to electrically tune the filter across the wavelength band. We report the first such demonstration of a tunable MEMS filter monolithically integrated on a HgCdTe detector. The filter structures, designed for operation in the 1.6-2.5 μm wavelength band, were fabricated directly on HgCdTe detectors, both in photoconducting and high density vertically integrated photodiode (HDVIP) detectors. The HDVIP detectors have an architecture that permits operation in the standard photodiode mode at low bias voltages (≤0.5V) or in the electron avalanche photodiode (EAPD) mode with gain at bias voltages of ~20V. In the APD mode gain values of 100 may be achieved at 20 V at 200 K. The FP filter consists of distributed Bragg mirrors formed of Ge-SiO-Ge, a sacrificial spacer layer within the cavity and a silicon nitride spacer membrane for support. Mirror stacks fabricated on silicon, identical to the structures that will form the optical cavity, have been characterized to determine the optimum filter characteristics. The measured full width at half maximum (FWHM) was 34 nm at the center wavelength of 1780 nm with an extinction ratio of 36.6. Fully integrated filters on HgCdTe photoconductors with a center wavelength of approximately 1950 nm give a FWHM of approximately 100 nm, and a peak responsivity of approximately 8 × 104 V/W. Initial results for the filters on HDVIP detectors exhibit FWHM of 140 nm.

The paper describes a platform technology for three-dimensional (3-D) integration of multiple layers of silicon integrated circuits. The technology promises to dramatically enhance on-chip signal processing capabilities of a variety of sensor and actuator devices hybridized with Si electronics. Among these applications are high performance infrared focal plane array detectors

This paper describes a technology platform being developed for three-dimensional (3-D) integration of thin stacked silicon integrated circuits (ICs). 3-D integration technology promises to dramatically enhance on-chip signal processing capabilities of a variety of sensor and actuator array devices hybridized with silicon read-out electronics. Currently, advanced 3-D integrated infrared focal plane array detectors are being developed within the DARPA vertically integrated sensor arrays (VISA) program. Here, we describe the 3-D integration process flow and demonstrations developed in the VISA program

A monolithically integrated low-temperature micro-electro-mechanical systems (MEMS) and HgCdTe infrared (IR) detector technology is introduced, implemented, and characterized. The ultimate aim of this project is to develop a MEMS-based optical filter, integrated with an IR detector, that selects narrow wavelength bands within the short-wavelength IR (SWIR) region of the spectrum. The entire fabrication process is compatible with two-dimensional IR focal plane array technology, and needs to be compatible with a proposed electrically tunable MEMS filter based on a Fabry-Perot optical cavity. The fabricated device consists of an HgCdTe SWIR photoconductor, distributed Bragg mirrors formed of Ge-SiO-Ge, a sacrificial spacer layer within the cavity, and a silicon nitride membrane for structural support. Mirror stacks fabricated on silicon, identical to the structures that will form the optical cavity, have been characterized to determine the optimum filter characteristics. The measured full-width at half-maximum (FWHM) was 34 nm at the center wavelength of 1,780 nm with an extinction ratio of 36.6. Fully integrated filters on HgCdTe photoconductors with a center wavelength of approximately 1,950 nm give a FWHM of approximately 100 nm, and a peak responsivity of approximately 8×104 V/W. The experimental results are in good agreement with the optical model, which takes into account mirror reflectivity, absorption within the cavity by the spacer material, and absorption by the silicon nitride support structure.

A low temperature MEMS process integrated with an infrared detector technology has been developed. The integrated microsystem is capable of electrically selecting narrow wavelength bands in the range from 1.6 to 2.5 mu m within the short-wavelength infrared (SWIR) region of the electromagnetic spectrum. The integrated fabrication process is compatible with two-dimensional infrared focal plane array technology. The demonstration prototypes consist of both HgCdTe SWIR photoconductive as well as high density vertically integrated photodiode (HDVIP (R)) detectors, two distributed Bragg mirrors formed of Ge-SiO-Ge, an air-gap optical cavity, and a silicon nitride membrane for structural support. The tuning spectrum from fabricated MEMS filters on photoconductive detectors indicates a wide tuning range and high percentage transmission. Tuning is achieved with a voltage of only 7.5 V, and the FWHM ranged from 95105 nm over a tuning range of 2.2 mu m to 1.85 mu m. The same MEMS filters, though unreleased, and with the sacrificial layer within the optical cavity, have been fabricated on planarised SWIR HDVIP (R) photodiodes with FWHM of less than 60 nm centred at a wavelength of approximately 1.8 mu m. Finite element modelling of various geometries for the silicon nitride membrane will also be presented. The modelling is used to optimize the filter geometry in terms of fill factor, mirror displacement versus applied voltage, and membrane bowing.

A monolithically integrated low temperature MEMS and HgCdTe infrared detector technology has been implemented and characterised. The MEMS-based optical filter, integrated with an infrared detector, selects narrow wavelength bands in the range from 1.6 to 2.5 mu m within the short-wavelength infrared (SWIR) region of the electromagnetic spectrum. The entire fabrication process is compatible with two-dimensional infrared focal plane array technology. The fabricated device consists of an HgCdTe SWIR photoconductor, two distributed Bragg mirrors formed of Ge-SiO-Ge, a sacrificial spacer layer within the cavity, which is then removed to leave an air-gap, and a silicon nitride membrane for structural support. The tuning spectrum from fabricated MEMS filters on photoconductive detectors shows a wide tuning range and high percentage transmission is achieved with a tuning voltage of only 7.5 V. The FWHM ranged from 95-105 nm over a tuning range of 2.2 mu m to 1.85 mu m. Finite element modelling of various geometries for the silicon nitride membrane will also be presented. The modelling is used to determine the best geometry in terms of fill factor, voltage displacement prediction and membrane bowing.

The monolithic integration of a low-temperature microelectromechanical system (MEMS) and HgCdTe infrared detector technology has been implemented and characterized. The MEMS-based tunable optical filter, integrated with an infrared detector, selects narrow wavelength bands in the range from 1.6 to 2.5 /spl mu/m within the short-wavelength infrared (SWIR) region of the electromagnetic spectrum. The entire fabrication process is compatible with two-dimensional infrared focal plane array technology. The fabricated device consists of an HgCdTe SWIR photoconductor, two distributed Bragg mirrors formed of Ge-SiO-Ge, a sacrificial spacer layer within the cavity, which is then removed to leave an air gap, and a silicon nitride membrane for structural support. The tuning spectrum from fabricated MEMS filters on photoconductive detectors shows a wide tuning range, and high percentage transmission is achieved with a tuning voltage of only 7.5 V. The full-width at half-maximum ranged from 95 to 105 nm over a tuning range of 2.2-1.85 /spl mu/m.