JRA-1

ISRSI Consortium Meeting Perugia, 17-01-2005

INAF/IASF (BO,PA)

This work is the preliminary activity in the framework of the development of an Itialian hard X ray (10-80 keV) telescope based on multilayer mirrors. The current project (funded for 6 months by the technological department of the Italian Space Agency, ASI) foresees the production of a multilayer test optics (OAB) and two small focal plane prototypes.

Low noise and power consumption ASIC for CZT/CdTe pixellated detectors

Politecnico di Milano

Construction of Pixel CZT detector prototype

IASF/CNR – Sezione di Palermo

Construction of microstrip CdTe detector prototype

IASF/CNR – Sezione di Bologna

Pixel detector

CZT (eV Products)

Geometric surface

1010 mm2

Active area 88 mm2

Thickness 1-2 mm

Number of pixels

256

Pitch

0.5 mm

(0.45 mm anodes, 0.05 mm gap)

Microstrip detector

CdTe

ACRORAD

Geometric surface

1010 mm2

Active area 88 mm2

Thickness 1-2 mm

Number strips

16+16 (crossed)

Pitch0.5 mm

(0.4 mm anodes, 0.1 mm gap)

ASIC main requirements

Dynamic range

10 keV – 100 keV

Power Dissipation

1 mW/ch

Multichannel layout

Pixel detector (16x16 pixels) and connection interface

The typical dark current level at 200 V bias is 0.2-0.3 nA/pixel

Microstrip detector and connection interface

(left) Photograph of the CdTe microstrip detector. On the opposite surface the strip layout is the same but in the othogonal direction; (right) A microscopic view of the same detector showing the bonding of each strip obtained using brass wire (150 µm wide) and conductive glue.

The microstrip detector mounted on a ceramic (Al2O3) bilayer substrate. In the vertical direction the two 8-pin connectors for the anode readout through the ASIC (DC coupling) are visible while in the opposite direction are the connectors for the cathode readout using 8+8 charge sensitive amplifier (AC coupling)

Technology : 0.8 m BiCMOS (AMS)

Energy Range : 10 keV – 100 keV (CdTe-CZT)

8 channels: Charge Preamplifier + Shaper (peaking time 1.2 s)

Power consumption : 0.5 mW/ch

The ASIC chip was first developed for thick CdTe/CZT array detectors for use in astrophysics applications over a wide energy range (20-2000 keV). The current design is a modification of the original ELBA (ELettronica a BAsso rumore e consumo) chip in which the dynamic range has been tuned to the 10-100 keV range.

The chip can be easily tuned to the I-V characteristics of the detector by means of the Ipre input that modifies the MOSFET operation current.

The new ASIC for the hard x-ray focal planeThe new ASIC for the hard x-ray focal plane

Response of an ASIC channel to signals simulating various photon energies

Channel vs energy linearity. The linearity of the single channels is better than 0.4% over the entire energy range

(from ~5 keV to 100 keV).

ASIC tests results (I)ASIC tests results (I)

Channel

1 2 3 4 5 6 7 8

Gain

0

2

4

6

8

10

12

14

Ipre = 1 nA

Ipre = 2 nA

Ipre = 5 nA

Ipre = 10 nA

Ipre = 20 nA

ASIC tests results (II)ASIC tests results (II)

The equivalent noise (rms) of each ASIC channel as a function of the MOSFET current

The ASIC gain and gain uniformity as a function of Ipre : the gain uniformity is always better than 5%.

The ASIC board I/F with the pixel detectorThe ASIC board I/F with the pixel detector

To optimize the coupling with the pixel detector and to be able to read out contiguous subsets of pixels (at least 88) the ASICs have been mounted on a ceramic board containing the bias circuit and filters. The major constraint on the design of this support is due to the layout of the detector output pins: the board thickness is limited to 2.5 mm and the lateral size to 82.5 mm.

Multiparametric electronics (up to 128 channels) with coincidence logic. Each pixel is connected to a separate electronic channel. Each event above the threshold is loaded into a de-randomisation FIFO, converted by a flash 12 bit ADC and then a 32 bit word is generated containing for each hit in the coincidence time window the pixel id and the 10 MSB of amplitude (energy).

The Multiparametric back-end electronicsThe Multiparametric back-end electronics

Data Handling ElectronicsGamma camera-likeGamma camera-like (16+16 channels) with position averaging. This system uses a resistor (16+16 channels) with position averaging. This system uses a resistor array (the XY/Strip small box in the scheme of Fig. 6 and in the picture shown in Fig. 7) as array (the XY/Strip small box in the scheme of Fig. 6 and in the picture shown in Fig. 7) as the interface between the detector channels and the ADC (12 bit). Each signal above a user-the interface between the detector channels and the ADC (12 bit). Each signal above a user-defined energy threshold is transmitted through the resistor array at each corner and defined energy threshold is transmitted through the resistor array at each corner and converted by 4 flash ADCs (Xa, Xb, Yc, Yd). The energy (10 bit) of the event is converted by 4 flash ADCs (Xa, Xb, Yc, Yd). The energy (10 bit) of the event is reconstructed by summing the 4 signals, while the position coordinates (x,y) are provided by reconstructed by summing the 4 signals, while the position coordinates (x,y) are provided by the weighted average (10 bit) of the signals in both directions by means of: the weighted average (10 bit) of the signals in both directions by means of:

x = (Xa – Xb)/(Xa+Xb) ; y =(Yc-Yd)/Yc+Yd) x = (Xa – Xb)/(Xa+Xb) ; y =(Yc-Yd)/Yc+Yd)

The final reconstructed data is loaded in a 32 bit unsigned word and transmitted to the The final reconstructed data is loaded in a 32 bit unsigned word and transmitted to the acquisition system using an handshake protocol.acquisition system using an handshake protocol.

Quick-Look Analysis

Pixel Detector (CZT) Spectral Resolution Pixel Detector (CZT) Spectral Resolution @ 60 keV@ 60 keV

Threshold ≈ 8 keVResolution ≈ 4.7 %

0,99 0,96 0,82 2,18

89,25

1,75 1,48 1,92 0,620

20

40

60

80

100

Pixel to total events ratio (%)

171 172 173 187 188 189 203 204 205

Pixel

Spatial distribution of counts when the beam is collimated on a single pixel. (right) the counts colour map of the incident and neighbouring pixels. (left) the histogram of the pixel to total counts ratio. Almost 90% of the photopeak (60 keV) counts are detected by the irradiated pixel.

Pixel Detector (CZT) Spatial resolution and Pixel Detector (CZT) Spatial resolution and pixel cross-talkpixel cross-talk