Development of a Radiation Hard CMOS Monolithic Pixel Sensor

Transcription

1 Development of a Radiation Hard CMOS Monolithic Pixel Sensor M. Battaglia 1,2, D. Bisello 3, D. Contarato 2, P. Denes 2, D. Doering 2, P. Giubilato 2,3, T.S. Kim 2, Z. Lee 2, S. Mattiazzo 3, V. Radmilovic 2 1 University of California at Berkeley, Berkeley, CA, USA 2 Lawrence Berkeley National Laboratory, Berkeley, CA, USA 3 University of Padova & INFN Padova, Padova, IT, EU

2 Rad-Hard CMOS Monolithic Pixels for... CMOS monolithic Pixel Sensors allow high-resolution, low material budget, high area/price ratio sensors. Commercially available manufacturing technologies. CMOS Pixels that are tolerant to several ~MRad ionising dose and to moderate non-ionising fluences ( n eq cm -2 ) could be employed in a wide range of scientific applications, from tracking and vertexing at HEP experiments to direct imaging in Electron Microscopy and beam monitoring. 1) High energy Physics Expected doses at the position of the innermost layer of vertex trackers: hybrid pixels necessary with very high non-ionising doses Monolithic Pixels favoured when higher resolution and smaller material budget are important Monolithic Pixels resistant to O(10 13 ) n eq cm -2 yr -1 and O(MRad) could be used as high-resolution outer layers, also for an LHC upgrade. Machine Luminosi ty [cm -2 yr -1 ] Non Ionising fluence [n eq cm -2 yr -1 ] Ionising dose [krad yr -1 ] LHC Super LHC ILC (500 GeV) CLIC (3 TeV) Super Belle Super B O(1000) RHIC /14

3 e - beam 2) Electron Microscopy 3) Beam monitoring CMOS monolithic pixels are being developed as an alternative to CCDs. Advantages: Single electron sensitivity (direct detection) Excellent Point Spread Function (thin collection layer, see picture) High readout speed (over 100 frame/s desired) Improved radiation hardness (ELT layout) Energies of interest ~ kev 500 e - /pixel dynamic range in imaging mode, ~10 6 e - /pixel/s in diffraction mode 10 rad/pixel/s, corresponds to ~ 1 MRad ionizing dose for typical annual usage Real time monitoring of hadron-therapy beam intensity and profile. Secondary electron emission from thin Al foil Desired granularity of 1 mm at 10 khz frame rate ~ e - (20 kev) mm -2 s -1 Exposures of ~minutes and ~1000 exposures/yr correspond to 5-10 MRad for typical annual usage 200 kev e - in CMOS sensor Metal + Oxide Epi layer Focal plane detectors for PEEMs systems (10 kev e - ).... 3/14

4 Ionizing radiation effects Charge trapping in field oxide and at the interfaces. Sensitive region around the charge collecting diode (electron accumulation, charge losses). 3T cell Non ionizing radiation effects Leakage current in diode from bulk damage. Sensitive region: shallow depleted region in the vicinity of the charge collecting diode, may lead to significant diode leakage current Low-resistivity epitaxial layer: type inversion expected only at high fluencies. Transistor leakage current may be an important contribution, especially for the reset node. Displacement damage threshold for e - on Si is about 260 KeV for free defects production, 5 MeV for clusters generation. 4/14

5 The LDRD2-RH chip ~70 e - ENC PO NW GR Developed in the frame of LBNL Laboratory Directed Research & Development (LDRD) grant. Manufactured in AMS 0.35 μm CMOS-OPTO (optimized low leakage current, 5 metal layers)process, with 14 μm nominal epitaxial layer thickness. 96x96 pixels, 20x20 μm 2, arrayed in several sub-sectors implementing different transistor layouts and different configurations of the charge collection diode. Simple 3-transistor (3T) pixel architecture. 2 sub-pixels with and without ELT layout. Serial readout, up to 25 MHz clock frequency. GR layout n-well diode with enclosing p+ guard-ring NW layout n-well diode with p+ guard-ring and thin oxide on top PO layout n-well diode with p+ rings, thin oxide on top and polysilicon ring 5/14

6 200 kev electrons irradiation Performed at the LBNL National Center for Electron Microscopy (NCEM). 200 kev electrons are expected to cause only ionising damage in Si (thr. energy for DD is 260 kev). Electron flux of ~2300 e - μm -2 s -1 ~9x10 5 e - /pixel/s (e.g. diffraction mode). Irradiation performed in steps up to a total dose of 1.11 MRad. Dark levels monitored as dose function. Tests performed at 6.25 MHz readout frequency 737 μs integration time. Chip covered with standard EM gold mesh (25 µm wire, 40 µm hole) during irradiation. After irradiation, the increase of leakage current in the exposed pixels gives a latent image of the mesh wires. Measurement of PSF ~30 μm possible, but e - scattering on mesh borders spoils the actual figure. Leakage current vs. dose for pixels with ELT layout PO No n-well diode NW GR 20 ADC = 100fA 6/14

7 Charged particle detection tests after 200 kev e - irradiation Cluster signal Cluster noise Pre irradiation Post irradiadion Pre irradiation Post irradiadion Energy deposited in a 3x3 pixel matrix measured with 200 kev and 1.5 GeV e - (from LBNL ALS) before and after 1.11 Mrad on the PO pixels. Energy spectrum fitted with Landau convoluted with Gaussian distribution to represent the noise. Change in gain of ~1.35. Good agreement between distributions after gain correction. 200 KeV e GeV e - Irradiation Before After Landau m.p.v. (5.57 ± 0.04) kev (5.54 ± 0.04) kev Gaussian noise (1.19 ± 0.04) kev (0.98 ± 0.03) kev 3 3 matrix noise (1.22 ± 0.20) kev (1.11 ± 0.20) kev Landau m.p.v. (3.05 ± 0.03) kev (3.37 ± 0.07) kev Gaussian noise (0.60 ± 0.06) kev (0.81 ± 0.07) kev 3 3 matrix noise (0.74 ± 0.01) kev (0.88 ± 0.01) kev 7/14

8 29 MeV proton irradiation Leakage current Noise in PO pixels 29 MeV protons, flux of ~3x10 8 pcm -2 s -1, irradiation in steps up to a total fluence of 8.5x10 12 p/cm 2 (~2 MRad). Dark level monitored in-between irradiation steps: at equal doses, a larger leakage current is associated with proton irradiation, hinting at a contribution from displacement damage. Among all ELT designs, best performance is obtained with PO pixels; noise of ELT cells only slightly increases at the highest doses while noise of standard cells doubles after ~1 MRad. All irradiations performed at the BASE Facility of the LBNL 88-inch Cyclotron; all tests performed at room temperature. 8/14

9 14 MeV neutron irradiation 55 Fe spectrum in PO pixels Noise in PO pixels 55 Fe peak 1-14 MeV neutrons produced from 20 MeV deuteron breakup on a thin target, flux of ~4x10 8 ncm -2 s -1, up to total fluence of 1.2x10 13 n eq /cm 2 No significant leakage current or noise increase after neutron irradiation: negligible bulk damage effects at the considered fluences. All irradiations performed at the BASE Facility of the LBNL 88-inch Cyclotron; all tests performed at room temperature. 9/14

10 Calibration with 55 Fe: comparison between irradiations Charge-to-voltage conversion gain calibration and single pixel noise as measured from the position of the 5.9 kev peak from 55 Fe spectra before and after the various irradiations on the PO pixels. No significant change in noise observed after the three irradiation. Change in gain of ~1.3 observed after ionising irradiation; no gain change after neutron irradiation. Before Irradiation After Irradiation Noise (130±6) e - ENC (122±6) e - ENC Gain (26.7±0.6) e - /ADC (36.3±0.8) e - /ADC P n Noise (128±5) e - ENC (126±5) e - ENC Gain (25.9±0.5) e - /ADC (34.9±0.9) e - /ADC Noise (69±3) e - ENC (64±5) e - ENC Gain (25.2±0.3) e - /ADC (24.4±0.4) e - /ADC 10/14

11 LDRD2-RH electrons imaging spatial resolution Electrons imaging Point Spread Function (PSF) measured on the Titan column with a thin 75 µm diameter gold wire taut over the detector. The use of the gold wire limited to a minimum the degradation due to the electron scattering at the borders. 75 µm Energy (KeV) 10 µm pixels 20 µm pixels ± 1 µm 13.7 ± 2.3 µm ± 1 µm 12.1 ± 2µm ± 1.6 µm 10.9 ± 2.3 µm 11/14

12 Latest results: atoms e - imaging with 1MPixel device Si lattice 2.5 ms integration time TEAM 1K detector 0.35 AMS opto process 1M pixel, 9.5 um pixel pitch Rad-hard design 25 MHz readout speed 16 parallel analog outputs Up to 400 Frames/s Thinned down to 50um to reduce backscattering FFT 12/14

13 Cluster imaging: a novel approach for high resolution imaging Cluster imaging: instead of integrating the e - flux into the detector, operate it in single particle tracking mode, retrieving each e - impact generated cluster. Reconstruct the image by summing up all the collected clusters coordinates. 75 µm Bright field Cluster imaging NIM A 608 (2009) Energy (KeV) Bright field Cluster imaging ± 0.6 µm 6.8 ± 0.35 µm ± 0.5 µm 2.7 ± 0.25 µm 13/14

14 Conclusions A CMOS monolithic pixel sensor with optimized layout of the pixel cell for improved radiation tolerance has been designed and tested up to 2 MRad ionising radiation and ~10 13 n eq /cm 2 non-ionising fluence. The chip implements transistors designed both with and without ELT rules, and different layout optimizations of the charge collecting diodes. The tests performed show an improved performance of pixels with ELT transistors, a thinner oxide on top of the diode surface and guard-rings around the diodes. This pixel layout has been implemented in a larger scale prototype deployed as a high-resolution (1 MPixel to 4 MPixel), fast (400 frame/s) and radiation-hard detector for the TEAM electron microscope at the LBNL National Centre for Electron Microscopy. 14/14