Statement of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Cash flows from operating activities
Net loss	$ (21,100)	$ (16,708)	$ (18,183)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	1,191	826	1,340
Loss on disposal of property and equipment		80
Stock-based compensation	2,048	1,141	416
Change in fair value of redeemable convertible preferred stock warrant liability		(372)	(15)
Non-cash loss on extinguishment of debt	185
Change in fair value of derivative liability		(798)
Non-cash interest expense	297	1,183	232
Compensation expense related to vesting of common stock to GLOBALFOUNDRIES	1,472	965	1,761
Changes in operating assets and liabilities:
Accounts receivable	(259)	(1,261)	339
Amounts due from related parties	(126)	78	102
Inventory	(3,871)	(893)	(431)
Prepaid expenses and other current assets	460	(860)	(77)
Other assets	(23)	(21)	(10)
Accounts payable	1,114	340	233
Accrued liabilities	(120)	56	428
Amounts due to related parties	(49)	(2,453)	3,328
Deferred income on shipments to distributors	(107)	387	(362)
Deferred revenue		(229)	229
Net cash used in operating activities	(18,888)	(18,539)	(10,670)
Cash flows from investing activities
Purchases of property and equipment	(3,070)	(1,040)	(1,295)
Net cash used in investing activities	(3,070)	(1,040)	(1,295)
Cash flows from financing activities
Proceeds from convertible promissory notes-related party		8,500
Proceeds from debt	12,000	1,500	8,000
Payments on debt	(8,356)	(1,325)	(3,000)
Payments of debt issuance costs	(49)	(40)	(130)
Payments on capital lease obligation	(7)	(198)	(226)
Proceeds from exercise of stock options and purchase of shares in employee stock purchase plan	1,593	48	4
Proceeds from issuance of common stock in connection with initial public offering, net of offering costs		33,864
Proceeds from issuance of common stock in private placement, net of issuance costs		4,650
Net cash provided by financing activities	5,181	46,999	4,648
Net (decrease) increase in cash and cash equivalents	(16,777)	27,420	(7,317)
Cash and cash equivalents at beginning of period	29,727	2,307	9,624
Cash and cash equivalents at end of period	12,950	29,727	2,307
Supplementary cash flow information:
Interest paid	467	806	421
Interest paid to related party		359
Non-cash investing and financing activities:
Purchase of property and equipment in accounts payable and amounts due to related parties	116
Purchase of inventory in accrued liabilities and amounts due to related parties	897
Purchase of property and equipment under capital lease obligations	$ 31		431
Conversion of convertible promissory notes into common stock		8,634
Issuance of warrants with debt			$ 307
Conversion of redeemable convertible preferred stock into common stock		64,642
Reclassification of warrant liability to additional paid-in capital		$ 65