MEMS-FTIRMEMS-FTIR

Overview

Connection example / Dimensional outline

Structure

Operation principle

Characteristics

Experiment exampleｓ

HAMAMATSU’ s technologies

HAMAMATSU’ s IR detector options

HAMAMATSU’ s NIR dispersive-type spectrometer options

FAQ

Next generation planning

C O N T E N T S

P. 2

P. 3

P. 4

P. 6

P. 7

P. 9

P.10

P.12

P.13

P.14

P.16

Compact NIR spectrometer with a built-in fingertip size MEMS-FTIR engine

The MEMS-FTIR is a compact and low cost Fourier transform infrared spectrometer, where a Michelson interferometer and an Infrared detector are packaged in a small housing. Spectral measurement or absorption measurement can be done simply by connecting to a PC via USB.

The MEMS-FTIR is a compact and low cost Fourier transform infrared spectrometer, which can be carried easily with one hand. All the functions due for driving the FT-IR excluding signal processing software are incorporated in a palmtop size housing. Spectral measurement or absorption measurement can be done simply by connecting to a PC via USB. A miniature FT-IR engine is a core of the MEMS-FTIR, and all the optical functions are built there. A Si chip having the FTIR optical functions is formed by fingertip size. A Michelson interferometer and an actuator for controlling a moving mirror in the interferometer are integrated into a Si wafer level package hermetically. A fiber for input light is mounted directly to a MEMS chip by passive alignment, which saves assembly cost remarkably. On the whole, a miniature FT-IR can be realized at dramatically low cost.

Overview

■ Specifications

(a) Construction

(c) Characteristics

Parameter Specification Unit

Optical interferometer

Spectral response range 1.15～1.65

8 (λ=1.65)

3029

5

12 (λ=2.05)

29

25

1.15～2.05

Wavelength resolution (FWHM)

SNR25 ℃

λ μmnm

dB

ms

dλ

40 ℃

Scan rate

Michelson interferometer --

-Photo-detector InGaAs PIN Photodiode

Optical input Optical fiber input (with FC connector)

Optical input core diameter 200 µm

Optical input NA 0.2 -

Electrical interface USB 2.0 -

Dimensional outline (W × D × H) 100 × 75 × 27 mm

Weight 190 g

Unit

Operating temperature＊

＊

1

Storage temperature＊1

2

＊3

＊4

+5 ～ +40 °C-20 ～ +70 °C

1: No dew condensation

＊

＊

2: About 29 cm-1 in wavenumber＊3: On conditions of about 600 μW white light input at a fiber (core diameter = 200 μm, NA = 0.2), 1s integration time ＊4: The minimum time to acquire an optical spectrum, converted into 200 Hz in measurement frequency

Symbol C12606-01 C12606-02 unit

MEMS-FTIR appearance MEMS-FTIR engine

(b) Absolute maximum rating

Parameter Specificatiion

Parameter

MEMS-FTIR

2

Measurement light is to be guided to an MEMS-FTIR via an optical fiber and an FC optical connector for detection of interference light (interferogram) . A measurement result is to be fed into a PC and then a spectrum can be obtained through Fourier Trans-fer (software for evaluation enclosed). The informa-tion on a MEMS actuator's operation for driving the FT-IR can be known accurately by measuring the capacitance of a device, so the spectrum with high degree of repeatability can be obtained.

C12606 series includes a USB cable only as a standard accessory.

Connection example

Dimensional outline (unit: mm)

Measurement example

Sample cell holder

Electrical signal

Optical signal

PC

Optical fiberconnection

Fiber light source(Halogen lamp)

MEMS-FTIR

100

USB Connector

Optical Connector

FC Fiber Type

MEMS Chip

Ground

27

MEMS is a lightweight miniature sized mechanical component realized by a Si wafer and semiconductor technologies. The wafer-level consistent processes give a full of mass-productivity. There are mechanical superiorities in high elasticity and in high stress resistance due to the Si-based technology. Multi-functions can easily be achieved by integrating circuits. Furthermore, physical load by light exposure can be neglected, so an application to a MEMS actuator is very optimum. We are actively promoting the compact MEMS-based IR spectrometers for realizing “field-use analytical tool” and then contributing to the society.

Compact MEMS-basedCompact MEMS-based

IR spectrometers creatingIR spectrometers creating

new concept spectroscopic analysisnew concept spectroscopic analysis● ● Plastic sortingPlastic sorting

● ● Food controlFood control● ● Smart agricultureSmart agriculture

● ● Exhaust gas monitorExhaust gas monitor● ● Alcohol monitorAlcohol monitor● ● Gasoline quality inspectionGasoline quality inspection

● ● Self-healthcareSelf-healthcare

Why MEMS ?

MEMS-FTIR

3

The MEMS-FTIR is formed by a fingertip size FT-IR engine, a control board, a photo-detector, input/output fibers,etc. The block diagram is herein shown.

Structure

The internal structure is show in the Fig.3. A Michel-son interferometer and an electrostatic actuator are formed on a single wafer monolithically with DRIE (Deep Reactive Ion Etching), which makes high accu-racy of 1 μm or less in tolerance on relative position of each optical component. No optical alignment after assembly is needed.

■ Ultra-compact FTIR engine

All the optical components of the Michelson interfer-ometer are formed on wall surfaces of Si fabricated. A beam splitter divides an input beam with Fresnel reflection (reflection 30% : transmission 70%) by utilizing a large difference in refraction between Si and air. A metal layer is evaporated on each surface of a moving mirror placed on the electrostatic actua-tor and a fixed mirror, which makes total reflection mirrors with high reflection (more than 98%).

(1) Michelson interferometer

[Fig.1] MEMS-FTIR structure [Fig.2] MEMS-FTIR block diagram

[Fig.3] Internal structure of MEMS-FTIR engine

@KACCC0737EA

@KACCC0711EA

[Fig.4] SEM image of Michelson interferometer

MEMS-FTIRengine Optical connector

Input optical fiber External interface

Control circuit

H.V.circuit

cap.sens.signal

cap.sensing (Cm)

Output optical fiberInterferogram

Optical detector

Actuationvoltage

Optical connector

MEMS-FTIRengine

Input optical fiber

Digital control circuit

Input optical fiberalignment guide

Output optical fiberalignment guide

Output optical fiberalignment guide

Input optical fiberalignment guide

Actuator control terminal

Michelsoninterferometer

MEMS actuator (electro-static actuator)

Eectro-static actuator Fixed mirror

Reflection fixed

Moving mirror

Moving mirror

BeamSplitter

BeamSplitter

Analog control circuit

Timing controldatain/outControl circuit fiber

(・External interface ・Analog circuit ・ Digital circuit)

Output optical fiber

Optical detector

USB connector

MEMS-FTIR

4

Guide grooves for fixing a fiber on a board are formed on the MEMS-FTIR, which is to omit manual alignment of an optical fiber, and to guide a signal light to the optical interferometer. The optical fiber is inserted into the guide groove and then fixed with resin after a chip of the FT-IR engine is mounted on a board, resulting in easy fiber alignment.

(2) Fiber guide

(3) Electrostatic actuator

■ Control circuit

A control board consists of an analog control part, a digital control part and an external interface part.The analog control part is connected to a fingertip size FT-IR engine for controlling it directly. Voltage necessary for driving an electrostatic actuator and signal for capacitance measurement to control a position of the electrostatic actuator are generated. A capacitance measurement value and an optical interference signal (interferogram) are received as input signals, and then transferred to the digital control part after amplification. The analog control part is formed by an electrostatic actuator control circuit, ASIC incorporating each amplifier, and a high voltage generator.The digital control part is for controlling operation timing of the analog control part, controlling timing of data acquisi-tion, setting the electrostatic actuator’s operation voltage and acquiring a measurement signal obtained and then amplified at the analog control part.The external interface part has a built-in MCU (Micro Controller Unit). The MEMS-FTIR is connected to a PC through USB interface. The MCU is for receiving the control signal of the electrostatic actuator, and then transferring the capacitance measurement data for Fourier transform and the optical interference signal data to the PC.

■ Photo-detector

A non-cooled InGaAs Photodiode, manufactured by Hamamatsu Photonics K.K., is used for a photo-detector, which has spectral response from 0.9 to 1.7 μm and 0.9 to 2.1 μm respectively. High sensitivity and low dark current are the main features of HAMAMATSU InGaAs Photodiodes.

■ Optical fiberInput light is transferred to a fingertip size FT-IR engine through an input fiber, and then to a photo-detector through an output fiber.

[Fig.5] Operation principle of electrostatic actuator　　　 (electrostatic force, spring, comb electrodes)

[Fig.6] SEM image of electrostatic actuator

@KACCC0713EA

dy = α・V2 ……… (1)　　α : voltage conversion efficient [m/V2]　

A moving mirror, which is a core of a Michelson interferometer, is driven by an electrostatic actuator fabricated with MEMS technologies. The electrostatic actuator is constructed by two pairs of segmented comb electrodes, which are fabricated by the plural number of flat electrodes placed in parallel and springs made of thin plates. By applying voltage between the segmented comb electrodes, a moving part of the segmented comb electrodes is to be moved close to a fixed part. Elastic force of returning to an original point is to be generated when a spring is extended, and a moving part is to stop when the elastic force and electrostatic force are balanced. A distance between the moving part and the fixed part is controlled by voltage between the segmented comb electrodes. A relation between actua-tor displacement (dy) and application voltage (V) can be expressed by the formula below.

Elastic force

Spring part

Spring part

Segmentedcombelectrodes

Segmentedcombelectrodes

Electrostatic force

MEMS-FTIR

5

Operation principle

FT-IR (Fourier Transform Infrared Spectroscopy) is one of IR spectrometers, in which optical coherence signals from two luminous fluxes are converted into spectrum by Fourier transform. The main advantages compared with a disper-sive type spectrometer with using a grating are as below ;

The FT-IR consists of an optical interferometer (Michelson interferometer), an IR light source, a photo-detector, a signal processor,etc. The IR light emitted by the source is converted into a parallel light by a lens, and enters the optical interferometer. A beam splitter there divides the light into two ; one is guided to a fixed mirror, and the other is to a moving mirror respectively first, and then each light is reflected back to the splitter. The two lights, returned to the beam splitter, are turned into one, and then guided to a sample. The output light becomes an optical interfer-ence light varied by the moving mirror, and the sample is exposed to it. The interference light after passing the sample is converted into an electric signal at the photo-detector, and then transferred to the signal processer as the interference signal (interferogram). A position of the moving mirror is monitored by a laser displacement sensor, and the position signal is also conveyed to the signal processor. The intensity signal of the interferogram and the moving mirror’s position signal can be converted into the spectrum’s intensity distribution at the signal processor.The resolution of the FT-IR is almost decided by a movable distance of the moving mirror and a spread angle in the optical interferometer. The wavelength resolution (∆ν) can be higher with the longer movable distance of the moving mirror (L unit: cm), which can be expressed by the formula below.

The wavenumber resolution of the spread angle of input light can be expressed by the formula below.

■ FT-IR (general desktop type)

■ MEMS-FTIR’s features

∆ν(L) = ……… (2)12L

∆ν(θ) = 2 (1 - cos θ) ν ……… (3)

ν: maximum wavenumber in measurement range

High S/N ration realized due to simultaneous measurements in the whole wavenumber range

High optical utilization available as an input slit can be enlarged for resolution common to the dispersive type

High accuracy and reproducibility of wavenumber as calibrated on each sample measurement with high wavelength stability laser

[Fig.7] FT-IR structure and operation principle

@KACCC0714EA

・

・

・

Absorbed spectrum

Inte

nsity

Inte

nsity

Inte

nsity

Position X

Position X

WavelengthWavelength

SpectrumDetector

Interferogram

Interferometer

Laser position monitor

Beamsplitter

IR source

FixedmirrorMovable

mirror

Sample

Fourier Transformcalculation by PCNumerical operation

Interferencefringes=Interferogram

The C12606 series’resolution is more influenced by the spread angle than the movable distance, which makes about 29 cm-1 in wavenumber resolution (wavelength resolution: 8 nm at 1.65 μm). The spectrometer performances of the FT-IR depend upon linearity of the interference signal detected at a photo-detector and a position accuracy of the moving mirror. From the fact that electrostatic capacitance in the segmented comb electrodes changes in proportion to the mirror displacement, so the mirror position can be controlled by monitoring a capacitance value in real time.

MEMS-FTIR

6

■ Wavelength resolution and spectral resolution measurement with laser light sources

A laser light source is ideal for evaluating wavelength accuracy and wavelength resolution of the FT-IR spectral characteristics. The measurement results of the laser lights are herein shown. The Fig.8 shows the inteferogram when the 3 wavelength laser lights are illuminated simultaneously with an optical coupler. The Fig.9 shows the spec-trum converted from the signal by Fourier-Transform. The wavelength resolution of about 8 nm at 1.6 μm wave-length is obtained. The Fig.10 shows how well the 2 wavelengths can be discriminated when the 2 laser lights, which are close in wavelength each other, are illuminated simultaneously. A difference by 5 nm can be detected sufficiently.

The above data were taken from the previous prototype (Example : wavelength resolution 10 nm at 1.7 μm), and those from the latest product after renovation are now under preparation.

Note:

MEMS-FTIR

7

[Fig.8] Interferogram (laser 1.3 μm, 1.45 μm, 1.6 μm simultaneously input, representative example)

@KACCB0321EA

[Fig.9] Spectrum (laser 1.3 μm, 1.45 μm, 1.6 μm simultaneously input, representative example)

@KACCB0322EA

[Fig.10] Two wavelengths discriminated (wavelengths of input laser: 1.540 μm + 1.545 μm, representative example)

@KACCB0323EA

CharacteristicsIn

terf

erog

ram

(ar

bitr

ary

valu

e)Intensity

(arb

itrar

y va

lue)

Optical path difference (μm) Wavelength (μm)

Wavelength (μm)

Rela

tive

inte

nsity

Peak

Peak

PeakPeak

Peak

■ Spectroscopic measurement of a white light

The Fig.11 and Fig.12 shows a white light’s interferogram and spectrum respectively, in which compensation of an InGaAs Photodiode’s spectral response is not done.

■ Absorbance measurement

[Fig.11] Interferogram of white light (C12606-01, representative example)

Spectrrum of white light(C12606-01, representative example)

@KACCB0324EA

[Fig.12]]

@KACCB0325EA

[Fig.13] Transmission spectrum of ethanol(C12606-01, representative example)

@KACCB0326EA

Absorbance of ethanol with a white light has been measured by the MEMS-FTIR, and its measurement example is shown in the Fig.13.

Optical path difference (μm)

Inte

rfer

ogra

m (

arbi

trar

y va

lue)

Tran

smis

sion

(%

)

Inte

nsity

(ar

bitr

ary

valu

e)

Wavelength (μm)

Wavelength (μm)

MEMS-FTIR

8

The above data were taken from the previous prototype (Example : wavelength resolution 10 nm at 1.7 μm), and those from the latest product after renovation are now under preparation.

Note:

Experiment examples

(1) Glucose solution measurement

(2) Plastic sorting

Glucose density can be estimated d with high degree of accuracy by using MEMS-FTIR.

The spectrum data obtained can make type judgment of transparent plastic plates(about 1mm thickness) possible.

Data provided by : Prof. Kawasumi, Kinki Univ.

Data provided by Hamamatsu Photonics K.K. - Central Research Lab.

＊

＊

Absorption spectrum - transparent plastics

0

0.2

0.4

0.6

0.8

1

1.2

1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2 2.1

Wavelength(μm)

Abso

rban

ce

PC(3mm thickness)

PET (0.5x0.5mm, a pce of a PET bottle)

PMMA (1mm thickness)

PS (1mm thickness)

PVC (1mm thickness)

-4

-3

-2

-1

0

1

2

3

1300 1400 1500 1600 1700

Auto

scal

ed a

bsor

banc

e

Wavelength （nm）

0% 0.1%0.25% 0.5%1% 2.5%5% 10%

・Method： Transmission (1mm quartz cell), Measurement

・Time： 2000 ms（5 ms × 400 times)

・Number of sampling： 8 levels of density x 6 times

・Data analysis： PLS Regression analysis

・Data pre-processing : smothing (75 points) + standardization

R2＝0.994SEP＝0.273RPD＝12.68

Standardization absorbance spectrum Result of glucose estimation

MEMS-FTIR

9

Hamamatsu’s technologies

Both optical interferometer and electrostatic actuator are formed monolithically on a single Si wafer with the technology of Si Deep Reactive Ion Etching. The interferometer’s components such as an input mirror, a beam splitter, a fixed mirror and a moving mirror can be fabricated with no tuning and at low cost due to intro-duction of high accuracy process by semiconductor lithography. High aspect ratio is realized by repeating etching and sidewall protection with a protection layer on Bosch process of Si Deep Reactive Ion Etching (Fig.14). The examples of Si wafer processes are herein shown in the Fig.15.

The so-called scallop (unevenness) is formed on a sidewall on the Bosch process, so the sidewall, which is an optical surface of the MEMS-FTIR, has to be flattened by removing the scallop. The Perpendicularity of the sidewall is impor-tant for avoiding a gap of an optical path due to refraction or reflection. Both flat and high perpendicularity sidewall can be formed by original technology of HAMAMATSU, which has been introduced into the MEMS-FTIR.

The FT-IR performances are decided by an optical interferometer, an actuator controlling a moving mirror, a photo-detector sensing a interference signal and a Fourier transform signal processor. Both size and price of the FT-IR depend upon the other contents than the signal processor since the sufficient performances can be brought out even with a low cost PC after the renovation of computer technologies in the recent years. The optics including the optical interferometer particularly require high degrees of accuracy and stability. Manual tuning had been mandatory as automated assembly was unlikely, which was making the FT-IR very costly. The MEMS-FTIR is by a cutting-edge technology, realizing integration of all the optics into a fingertip size MEMS chip and resulting in both miniature size and low cost. Various MEMS technologies are introduced into the fingertip size MEMS-FTIR engine. Both Si Deep Reactive Ion Etching and wafer level packaging are particularly important.

■ Si Deep Reactive Ion Etching

[Fig.14] Principle of Bosch process

① Isotropy etching by fluorine‐containing gases

② State after Isotropy etching

③ Formation of protection layer

④ Removal of protection layer by ion shock

@KACCC0712EA

[図15] High aspect ratio (10:1) achieved by Bosch process, etching example

Scallop size

MEMS-FTIR

10

■ Wafer level packaging

Malfunction should occur if there would be fine particle or a moisture content attached to a gap between segmented comb electrodes of a MEMS actuator; an inter-electrode space is as narrow as a few μm. A particle or a moisture content has to be avoided at production processes as well as during use in various environments after delivery. The actua-tor has to be protected environmentally before diced as the particle or the moisture attached are possible to occur during a dicing processing,etc. Therefore sealing the whole MEMS chip into a hermetic package in advance is a useful method.The wafer level packaging for capping in the wafer state (before diced) is done on the fingertip size FT-IR engine. So-called surface activated bonding is used for bonding wafers, which makes molecular level bond-ing without using adhesive glue possible. It results in low cost due to Si wafer usable for a capping material, high reliability, and high productivity.

[Fig.16] Wafer level packaging technology(fabrication of miniature FTIR engine)

① Wafer bonding

② Dicing

Capping wafer

Device wafer

MEMS-FTIR

11

HAMAMATSU infrared detectors

MEMS-FTIR

12

0 1 2 3

1.7

InGaAs PIN photodiodes

InGaAs image sensors

0 5 10 15 20 25

1 3.2

1

1

3

1

1

1 6.7

0.9

0.9 1.9

0.9

2.6

5.2

5.5

5.8

25

13.5

1

0.2

10

2.550.9

2.1

2.550.5

4.85

1 3.8

Spectral response range (µm)Product name serutaeF

Product nameSpectral response range (µm)

serutaeF

PbS photoconductive detectors

PbSe photoconductive detectors

InSb photoconductive detectors

InSb photovoltaic detectors

InAs photovoltaic detectors

InAsSb photovoltaic detectors

1 25MCT (HgCdTe) photoconductive detectors

MCT (HgCdTe) photovoltaic detectors

Thermopile detectors

Two-color detectors

Si + PbS

Si + PbSe

Si + InGaAsInGaAs + InGaAs

Photon drag detector

0.9

0.5 1.7

2.55

0.2

0.32

• Standard type• High-speed response, high sensitivity, low dark current• Available various types of photosensitive areas, arrays and packages• For optical measurement around 1.7 µm• Available TE-cooled type• For optical measurement in the band of water contentabsorption (1.9 µm)

• Available TE-cooled type

• Types for spectrophotometry and WDM monitor, andhigh-speed type available

• For NIR spectroscopy• Available TE-cooled type

• Short wavelength enhanced type• Can detect light from 0.5 µm

• Photoconductive detectors whose resistance decreases with the input of infrared light• Can be used at room temperatures in a wide range of applications

• Detects wavelengths up to 5.2 µm• Offers higher response speed at room temperatures compared to other detectors used in the same wavelength range. Suitable for a wide range of applications such as gas analyzers.

• Detects wavelengths up to around 6.5 µm, with high sensitivity over long periods by thermoelectric cooling

• High-speed and high sensitivity in so-called atmospheric window (3 to 5 µm)

• Covers a spectral response range close to PbS but offers higher response speed

• Various types with different spectral response range are provided by changing the HgTe and CdTe composition ratio.• High sensitivity photoconductive detectors whose resistance decreases with the input of infrared light• Available with TE-cooled type and cryogenic dewar

• Wide spectral response range from UV to IR• Uses two detectors with different spectral response ranges, mounted one over the other along the same optical axis

• High-speed response and low noise

• High-speed detector with high sensitivity in 10 µm band (for CO 2

laser detection)• Room temperature operation with high-speed response

• Sensors that generate thermoelectromotive force in proportion to the energy level of incident infrared light

• Infrared detectors in the 5 µm spectral band, with high sensitivity and high reliability• High-speed response

HAMAMATSU’s NIR dispersive-type spectrometer options

These mini-spectrometers use an InGaAs linear image sensor designed for near infrared detection. Their spec-tral response range is from 0.9 to 1.7 μm or from 1.1 to 2.2 μm. TE-cooled and low noise types are also provided.

Features

Mini-spectrometers C11482GA, C9913GC, C9914GB

±

Dispersive spectrometer

*1: Depends on the slit opening. Values were measured with the slit listed in the table “ ■ Structure/Absolute maximum ratings”.*2: Measured under constant light input conditions*3: When monochromatic light of the following wavelengths is input, spectral stray light is defined as the ratio of the count me asured at the input wave-length, to the count measured in a region of the input wavelength ±40 nm.C9406GC, C9913GC: 1300 nm, C9914GB: 1650 nm

Spectral response range nm

Spectral resolution (FWHM)*1 nm

Wavelength reproducibility *2 nm

Wavelength temperature dependence nm/˚C

Parameter

1100 to 2200

8 max.

900 to 1700

7 max.

-0.2 to +0.2 -0.4 to +0.4

900 to 1700

7 max.

-0.2 to +0.2

-0.02 to +0.02 -0.04 to +0.04-0.02 to +0.02

Spectral stray light*1 *3 dB-35 max.

UnitTG-NIR TG-cooled NIR-II

C9406GC C9914GB

TG-cooled NIR-I

C9913GC

■ Optical characteristics

A/D conversion bits

Integration time ms

Interface -

Consumption current of USB bus power mA

Parameter

16

5 to 10000 5 to 1000

USB 1.1

250 max.

UnitC9913GC

■ Electrical characteristics

C9406GC C9914GB

■ Demensional outline (unit: mm, tolerance unless otherwise noted: ±0.5)

KACCA0146EC

38.5

16.0

105.5

41.8

68.6

85.6

49.7

(40.

0)

20.0

85.6

(2×) M3 tap depth 5.0from backside

Weight: 270 g

Application examples

G9204-512D

Built-in InGaAs linearimage sensor

Built-in TE-cooled typeInGaAs linear image sensor

G9204-512S

C9406GC

C9914GB

● Built-in near infrared InGaAs linear image sensor

● High throughput due to transmission grating made of quartz

● Highly accurate optical characteristics

● C9406GC: No external power supply required (Uses USB bus power)(C9913GC, C9914GB: Each requires 5 V and 12 V power supplies)

● Low noise measurement (C9913GC, C9914GB)

● Compact design for easy assembly

● Wavelength conversion factor is recorded in internal memory

MEMS-FTIR

13

14

MEMS-FTIR

FAQ

MEMS-FTIR Desktop FTIR Dispersive type

Detector single CH single CH array type

SNR (rough) 30dB approx. 45dB approx. 35dB approx.

Size small large medium

Price low high medium

Q： What are main differences from the conventional IR spectrometers ?A： The MEMS-FTIR is an embedded module featuring compactness and low cost.

Q： The overall size reduction is to be tried by employing a MEMS-based blackbody source or an IR-LED. Are there any light sources recommended for a purpose of downsizing ?

A： At this point, there are no likely candidates of the MEMS-based blackbody source in consideration of restrictions in its output power, the MEMS-FTIR’s SNR. a heatsink function on a driver circuit,etc. An IR LED seems a right approach, but there is limitation in market availability unfortunately.

Q： What light source is recommended for use with the MEMS-FTIR ?A： The light below is used for Hamamatsu’s own demonstration. This is not a recommendation, but it should be worth

trying.

Q：What else should be prepared for a spectroscopic measurement besides the MEMS-FTIR ?A： A connection example is as shown in the 3rd page. The MEMS-FTIR C12606 series includes a USB cable, so

an appropriate light source, a sample cell holder and an optical fibers should be prepared by a user.

Note: An optical fiber below for input to a MEMS-FTIR main body is recommended. - FC/PC type connector - S.I (Step Index) fiber, 200 μm core diameter, NA=0.2

Q：Are there any significant differences from a dispersive type spectrometer ?A： On a condition of sufficient light input (e.g., about 600 μW white light input at a fiber (core diameter=200 μ

m, NA=0.2), there is no significant difference between a dispersive type spectrometer and a MEMS-FTIR. However, the dispersive type spectrometer has an advantage of increasing the input light amount by making an integration time long, so it can have higher sensitivity than the MEMS-FTIR on a fait light detection.

Q：What is light utilization efficiency of the MEMS-FTIR ?A： It is about 0.2 % on the present model of a MEMS-FTIR (C12606-01/-02), which is almost due to spread of

light output from a fiber. There is a restriction in optical size, and no collimate lens is provided on an input part of the MEMS, which result in limited light utilization efficiency. A desktop FTIR employs an optical system of several cm or even larger, and utilizes the parallel light, which makes the loss minimized. There is certainly a remarkable gap between the MEMS-FTIR (mm scale or even smaller) and the desktop FTIR (cm scale), which can not be avoided anyway. As a mid-term renovation theme, how to incorporate the collimate lens into the MEMS-FTIR is to be investigated for relieving the loss. In fact, a theoretical value of the light utilization efficiency on a dispersive type spectrometer is several %, which is related to a relation between resolution and input slit, and a grating’s diffraction efficiency. As an ultimate target, the MEMS-FTIR is being tried to improve for being comparable with the dispersive type spectrometer in the light utilization efficiency.

- Halogen lamp (12 V, 50 W), about 600 μW is obtained at fiber output (200 μm core diameter, NA=0.2), which comes from an InGaAs PD’s sensitivity of about 0.9 A/W.

Q： What is a relation between wavelength and wavenumber ?A： Resolution of FTIR is generally defined by wavenumber (cm-1), which is decided by the FTIR interferometer’s

optical path difference) and expansion of input beam guided to the interferometer. The C12606 series’ resolution is about 29 cm-1 in wavenumber and 8 nm (λ=1.65 μm) in wavelength.

Q： What type of software is to be provided with the MEMS-FTIR ?A： Acquisition of interferogram and conversion into spectrum are supported on a basic operation. Software library

and DLL are being prepared for allowing a user to handle the data acquisition and calculation.

Q： Which types of interfaces are to be prepared ?A： The C12606 series is compatible to USB2.0, but I2C and SPI are planned to prepare on the next generation

model shown in a later page as it is subject to be an embedded module.

Q： What is power consumption ?A： It is 5 V/250 mA approx., and the MEMS-FTIR can be operated with USB bus power.

Q： Are there any plans about correspondence to an SMA fiber　?A： Yes, this will be an option in the near future. An FC connector is now adapted for a reason of little optical loss

due to small displacement. The SMA fiber option is to be considered along with enlargement of fiber core diameter. Regarding an FC-SMA conversion fiber, consult with us, please.

Q： How can an actuator be operated ?A： A moving mirror of the MEMS-FTIR’s Michelson interferometer is made up with a electrostatic actuator

fabricated by the MEMS technology. It consists of plural plates of so-called comb electrodes in 2 pairs and springs formed by a thin and long plate as shown in the 5th and 6th pages. The actuator can be operated by applying voltage to the inter-electrodes. A position of the moving mirror can be monitored by measuring the capacitance change. The current MEMS-FTIR version is at static operation only, and a resonant mode type is also under development.

Q： How can calibration be done ?A： The capacitance of a electro-static actuator and a position of a moving mirror is measured with a 1.3 μm LD

for calibration, and the calibration data is to be appended with each unit on delivery. Regarding periodic re-calibration after delivery, we think a maintenance-free FTIR is a basic concept, but are also planning to deal with re-calibration by having a unit returned to the factory (liable for cost).

MEMS-FTIR

15

Q： Are there any restrictions on a PC or OS ?A： The types below are recommended for use with the MEMS-FTIR.

□ Hardware specifications: - CPU CORE2DUO: 2.0 GHz or higher - RAM: ２ GB or more - HDD free space: 800 MB or more (Windows system version)

□ OS: Windows XP (x86, x64) Windows Vista (x86, x64) Windows 7 (x86, x64)

Q： What is the minimum measurement time ?

A： The measurement frequency is about 200 Hz. A cycle of a moving mirror gives 2 data at back and fourth, so each measurement requires at least about 5ms/time. For obtaining a fair level of SNR, the data integration of about 200 times is recommended, which makes the total measurement time of about 1s. In addition, the display of a spectrum requires some time for data processing,etc, which is about a few ten seconds with a present circuit and software of the MEMS-FTIR as well as the performances of an ordinary PC.

Q： What degree of durability does the MEMS-FTIR have ?A： The moving mirror’s continuous operation has been tested up to 5 ×108 times, showing no degradation then.

On an actual application, this experiment does not seem sufficient, so the continuous operation at a high temperature (e.g., Ta=40 ℃) is planned to do.

Q： Can a MEMS chip only be purchased ? A： The whole set of a MEMS-FTIR (i.e., MEMS chip, ASIC and software) is subject to supply. Operation of the

MEMS chip as an FTIR includes a lot of know-how including the software, so there is no way to ensure the operation of a MEMS chip only at a user, which would make our technical support unlikely.

Q： Are there any plans on a MIR type ? A： Yes. We are aware this technology can give more benefits at a longer wavelength due to a single channel

detector usable for the MEMS-FTIR’s unlike a high cost array type sensor necessary for a dispersive type spectrometer although the first model of he MEMS-FTIR is NIR (i.e., up to 1.65 μm, 2.05 μm) only. A wide range of MIR detector options are being available in Hamamatsu’s line up, so we are trying to develop a MIR-type MEMS-FTIR along with renovation of the MIR detector. InAsSb based detectors extended up to 8 μm have been ready, and further extension up to 10 μm is also being tried. In fact, there are a few other difficulties due to overcome. A suitable optical fiber that transmits the MIR light should be selected, a MEMS engine itself should be renovated for being due resolution in wavenumber at a MIR range (e.g., longer moving distance of an electro-static actuator).

Q： Are there any plans for further downsizing ?A： Yes, this is the next theme of our challenges. Downsizing will be achieved by building more functions in an

ASIC chip and incorporating a PD chip into the MEMS-FTIR engine (non-cooled type only), making the overall size less than half.

Q： Do you have a plan to release a cooled type ?A： We have no plan for now as the overall noise of the present model of a MEMS-FTIR (C12606-01/-02) is

mostly deiced by an amplifier rather than a Photodiode’s dark current, so no significant improvement in detection performance can be expected by cooling. A MIR type is one of a mid-term development them, which may require cooling as the dark current of a photodiode covering a MIR range can not be neglected, so a cooled type option is to be prepared at the same time of the MIR type MEMS-FTIR.

MEMS-FTIR

16

MEMS-FTIR

www.hamamatsu.com

HAMAMATSU PHOTONICS K.K., Solid State Division1126-1 Ichino-cho, Higashi-ku, Hamamatsu City, 435-8558 Japan, Telephone: (81) 53-434-3311, Fax: (81) 53-434-5184U.S.A.: Hamamatsu Corporation: 360 Foothill Road, P.O.Box 6910, Bridgewater, N.J. 08807-0910, U.S.A., Telephone: (1) 908-231-0960, Fax: (1) 908-231-1218Germany: Hamamatsu Photonics Deutschland GmbH: Arzbergerstr. 10, D-82211 Herrsching am Ammersee, Germany, Telephone: (49) 8152-375-0, Fax: (49) 8152-265-8France: Hamamatsu Photonics France S.A.R.L.: 19, Rue du Saule Trapu, Parc du Moulin de Massy, 91882 Massy Cedex, France, Telephone: 33-(1) 69 53 71 00, Fax: 33-(1) 69 53 71 10United Kingdom: Hamamatsu Photonics UK Limited: 2 Howard Court, 10 Tewin Road, Welwyn Garden City, Hertfordshire AL7 1BW, United Kingdom, Telephone: (44) 1707-294888, Fax: (44) 1707-325777North Europe: Hamamatsu Photonics Norden AB: Smidesvägen 12, SE-171 41 Solna, Sweden, Telephone: (46) 8-509-031-00, Fax: (46) 8-509-031-01Italy: Hamamatsu Photonics Italia S.R.L.: Strada della Moia, 1 int. 6, 20020 Arese, (Milano), Italy, Telephone: (39) 02-935-81-733, Fax: (39) 02-935-81-741China: Hamamatsu Photonics (China) Co., Ltd.: 1201 Tower B, Jiaming Center, No.27 Dongsanhuan Beilu, Chaoyang District, Beijing 100020, China, Telephone: (86) 106586-6006, Fax: (86) 10-6586-2866

Information described in this material is current as of May, 2014.Product specifications are subject to change without prior notice due to improvements or other reasons. Before assembly into final products, please contact us for the delivery specification sheet to check the latest information.Type numbers of products listed in the delivery specification sheets or supplied as samples may have a suffix "(X)" which means preliminary specifications or a suffix "(Z)" which means developmental specifications.The product warranty is valid for one year after delivery and is limited to product repair or replacement for defects discovered and reported to us within that one year period. However, even if within the warranty period we accept absolutely no liability for any loss caused by natural disasters or improper product use.Copying or reprinting the contents described in this material in whole or in part is prohibited without our prior permission.

Next generation plan

The next generation MEMS-FTIR will realize pocket-size by incorporating more functions into an ASIC (Application Specific Integrated circuit) chip.

■ Internal structure 　（SEM photo）

2ndgeneration

More functions to be integrated

PC

Smart phone,etc

USB

I2C/SPI

control

data

data/control

70V

X

70V

X

ASIC FPGA

ADC

ADC

High-VoltageCircuitry

MEMSInterferometer

MCU

XTAL

Light

ASIC

X

X

MEMSInterferometerLight

Electronics Board

Photo-detectorElectrostaticactuator

・ Circuit on current model

・ Circuit on next generation model

100mm

75mm

100mm

75mm

40mm50m

m

Photo detector

・ ASIC: more functions ー integration of ADC, FPGA,etc・ FTIR engine: more functions

・ Interface: I2C/SPIASIC ‒ more functions

DownsizingHigh throughput

Size on current model

ー embedding photodetector & lens, and increase in scan speed

Size on next generation model (under development)

Photodetector